Blootstelling aan lood tijdens zwangerschap is in verband
gebracht met obesitas tijdens de kindertijd
Een recente - door de Institutes of Health betaalde - studie vond
een verband tussen hoge niveaus van lood tijdens de zwangerschap en
(extreem) overgewicht bij uit die zwangerschap geboren kinderen. Kinderen van vrouwen met een grote hoeveelheid lood in het bloed
hebben meer kans op overgewicht of obesitas in vergelijking met
kinderen van moeders met weinig lood in hun bloed. Dit concludeert
een studie die werd gefinancierd door de National Institutes of
Health en de Health Resources and Services Administration.
Blootstelling aan lood blijkt van invloed op
vruchtbaarheidsgehalte
Sinds een paar jaar is Flint, Michigan, in het nieuws
vanwege ontdekkingen in relatie tot lood in de
watervoorziening. Uit nieuw onderzoek naar de impact van
blootstelling aan lood (in de lucht en bovengrond) op
vruchtbaarheid in de VS bleek dat blootstelling van
invloed is op zowel vrouwen als mannen. Het is de eerste
studie waarin causaal verband wordt aangetoond van de
relatie tussen blootstelling aan lood en het
vruchtbaarheidsgehalte in de jaren 1980-2000.
Staat het loodgehalte van kinderen in bloed in
verband met crimineel gedrag?
Waar het op neer komt: Onderzoekers vonden geen
consistente associatie tussen blootstelling aan lood als
kind en crimineel gedrag als volwassene in Nieuw
Zeeland, waar een lagere sociaaleconomische status - die
de associatie in omstandigheden met sociaaleconomische
ongelijkheden verstoort - minder speelt.
Vermindering blootstelling lood in kindertijd en daling van
criminaliteit
Volgens onderzoek aan de Princeton- en Brown
University verhoogt blootstelling aan lood tijdens de kleutertijd de
kans dat kinderen tijdens hun schooljaren moeten worden
geïnterneerd. Omgekeerd leidt een daling van de blootstelling tot
minder antisociaal gedrag en kan dus de laatste decennia een
belangrijke factor zijn voor de daling van de misdaad.
Blootstelling van Dunedin kinderen aan lood in verband met
lagere IQ
Extreem hoge niveaus van lood in Nieuw-Zeeland steden in de jaren
1970 en 1980 lijken verantwoordelijk voor een verlies van
intelligentie en beroepsziektes onder volwassenen van vandaag. Het meest recente onderzoek van de Universiteit van Otago
langlopende Dunedin Study Nieuw-Zeeland laat zien dat onder meer dan
500 kinderen die opgroeiden in het tijdperk van gelode benzine, die
zijn blootgesteld aan lood een lager IQ en sociale status haden op
de leeftijd van 38, ten opzichte van leeftijdsgenoten die aan minder
waren blootgesteld.
Lage lood waardes in kinderen hebben negatief effect op
schoolcijfers
Een nieuwe studie die data uit een Rhode Island's
onderzoeksprogramma en data van herhaalde loodtesten gebruikt
laat zien dat een lage blootstelling
aan lood onder scholieren slechte leerresultaten kan voorspellen
in de jaren die volgen. (Bron Brown University)
Hoe een Amerikaanse stad vergiftigd werd met lood in het
drinkwater
Blootstelling aan lood beïnvloedt de slaap van kinderen
Een nieuw onderzoek aan de Universiteit van Pennsylvania ‘School
of Nursing (Penn Nursing)’ laat zien dat blootstelling aan lood in
de vroege jeugd een verhoogd risico geeft op slaapproblemen en
overmatige slaperigheid overdag tijdens de latere kindertijd.
Onderzoekers ontdekken bewijs dat blootstelling aan lood
van moeders gevolgen kan hebben voor volgende generatie
Een team van onderzoekers aan de Wayne State University heeft
ontdekt dat moeders met een hoog loodgehalte in hun bloed niet
alleen de cellen van het ongeboren kind, de foetus, kunnen
aantasten, maar ook die van hun kleinkinderen.
Algemene methode om het loodgehalte van drinkwater te
verlagen kan tegengestelde effect hebben
Nieuw onderzoek heeft aangetoond dat het verlagen
van de pH van de gemeentelijke watervoorzieningen, een
gemeenschappelijke strategie gebruikt om de vrijlating van oplosbaar
lood uit sanitaire materialen te controleren, de corrosie van
gietijzer kan beïnvloeden, wat resulteert in verhoogde niveaus van
zowel deeltjes ijzer als deeltjes lood in drinkwater .
Lood in het bloed van kinderen gerelateerd met
gedrags- en emotionele problemen
Uit een onderzoek gefinancierd door het National
Institute of Environmental Health Sciences (NIEHS), onderdeel van
het National Institutes of Health, blijkt dat emotionele- en
gedragsproblemen bij kinderen optreden zelfs na een lage
blootstelling aan lood en de problemen erger worden naarmate het
loodgehalte verhoogt.
Bewijs voor effecten van giftig lood en crimineel gedrag
Als misdrijfcijfers dalen, geven politici
zichzelf graag een schouderklopje voor hun strenge beleid.
Maar er is een nieuwe theorie die steeds geloofwaardiger
wordt en duidelijk maakt waarom het landelijke geweld sinds
1990 gedaald is, en het heeft niets te maken met het
crimineel rechtssysteem. Een artikel in “Chemical &
Engineering News” toont duidelijk de toenemende cijfers
waaruit zouden blijken dat het verwijderen van lood uit
benzine en verf een cruciale rol heeft gespeeld.
Hogere gehaltes lood in bloed aangetroffen bij
kinderen woonachtig in de buurt van gifbelten, met als
gevolg een lager IQ
Een onderzoeker van Mount Sinai schat dat
blootstellen aan lood geestelijke achterstand bij 6 op de
1000 kinderen, die in de buurt van zulke plaatsen wonen, kan
veroorzaken. Kinderen die in de buurt wonen van
gifbelten in landen met een laag en gemiddeld inkomen zoals
India, de Filippijnen en Indonesië kunnen een hoger
loodgehalte in hun bloed ondervinden en een hogere
verbreiding van geestelijke achterstand, volgens een
onderzoek dat werd gepresenteerd door Kevin Catham-Stephens,
arts en pediatrisch mandaathouder voor Gezondheid en Milieu
bij de Icahn Universiteit voor Geneeskunde van Mount Sinai,
tijdens de jaarlijkse bijeenkomst van de Verenigingen van
Universiteiten voor Kindergeneeskunde (PAS) op 6 mei jl. in
Washington, DC.
Lood treft men aan in oude verven (met
inbegrip van die op oud kinderspeelgoed), in de bodem, in oude
leidingen, in water, in de atmosfeer, in loodhoudende
brandstoffen van voertuigen zelfs in drinkbekers. Bij hoge
dosering is het dodelijk, maar veroorzaakt ook schijnbaar
triviale symptomen zoals hoofdpijn. Bij kinderen leidt het ook
tot schade aan de organen, de nieren in het bijzonder en het
zenuwstelsel inclusief de hersenen.
Philippe Grandjean, adjunct professor of
environmental health, discusses the findings of a report by the European Food Safety
Authority (EFSA), which concludes there is no known safe exposure to lead.
Lood vergiftiging - Govt.
gewaarschuwd Zamfara tienmaal
Tien verschillende brieven werden gestuurd
door het federale ministerie van mijnbouw en staal ontwikkeling in de Nigeriaanse deel
staat Zamfara om te waarschuwen voor de gevaren van illegale mijnbouwactiviteiten (vóór
het recente incident van lood vergiftiging die het leven van honderden kinderen eiste).
Pediatrician explains the frightening
symptoms and permanent disabilities of lead poisoning in children. Besides lead paint,
pesticides and other harmful chemicals in the home can cause similar serious and permanent
health problems.
Kleine hoeveelheden lood kunnen de
nieren van kinderen beschadigen
Kleine hoeveelheden lood in het lichaam van
gezonde kinderen en tieners kunnen hun nierfunctie verslechteren. Ook als het gaat om
hoeveelheden die ver beneden de toegelaten normen van de US-Centra voor Ziektecontrole en
-Preventie liggen Dit meldt een studie van het John Hopkins Kindercentrum, op 11 januari
in de Archieven der Interne Geneeskunde gepubliceerd .
- loden waterleidingen (oude huizen)
- loodhoudende verfsoorten in oude huizen
- benzine (tot 1984)
- sigarettenrook
Loden leidingen
Loden drinkwaterleidingen zijn verboden:
als looddeeltjes in het water belanden, kunnen ze namelijk de gezondheid bedreigen. In de
bouw zijn loden leidingen sinds 1960 al in de ban, maar in oudere huizen kunnen ze nog
voorkomen. Lood is vroeger algemeen gebruikt voor drinkwaterleidingen. In de leidingen
kunnen echter kleine metaaldeeltjes loslaten en zo in het drinkwater komen. De hoeveelheid
lood die een volwassene binnen kan krijgen via drinkwater uit loden leidingen, ligt ruim
onder de wettelijke norm; maar kleine kinderen zijn veel gevoeliger voor lood. Teveel lood
kan leiden tot schade aan het zenuwstelsel (leerstoornissen), bloedarmoede, miskramen en
aangeboren afwijkingen en nierbeschadiging. Zuigelingen die flessenvoeding krijgen met
water uit loden leidingen, kunnen al snel een ongezonde hoeveelheid binnen krijgen. Dat
kan schadelijk zijn voor de ontwikkeling van hersenen en zenuwstelsel: het kan leiden tot
een wat lagere intelligentie (een tot vijf IQ-punten) en tot gedragsveranderingen. Eind
2006 moesten alle loden leidingen in huurwoningen, en negentig procent van de
loden leidingen in particuliere woningen zijn gesaneerd.
- De verstoring van de biosynthese van
hemoglobine en bloedarmoede
- Een verhoging van de bloeddruk
- Nierbeschadiging
- Miskramen
- Verstoring van de zenuwstelsels
- Hersenbeschadiging
- Afgenomen vruchtbaarheid bij mannen door beschadiging van het sperma
- Verkleinde leermogelijkheden bij kinderen
- Gedragsstoornissen bij kinderen, zoals agressie, impulsief gedrag en hyperactiviteit
Lood kan via de placenta van de moeder bij een foetus terecht komen. Daardoor kan het
ernstige schade toebrengen aan het zenuwstelsel en de hersenen van ongeboren kinderen.
Belangrijke informatie voor
eigenaren van huizen die gebouwd zijn voor 1960
We hebben in Nederland - gelukkig -
drinkwater van een zeer goede kwaliteit. Natuurlijk willen we dat zo houden. Daarom is het
de bedoeling om voor 2005 alle loden leidingen te vervangen. Via loden leidingen komt er
namelijk lood in het drinkwater. Hoewel lood in het lichaam voor vrijwel niemand risico
oplevert, hoort het er niet thuis. De waterleidingbedrijven en het ministerie van VROM
zullen hun steentje bijdragen om de lodenleidingen te vervangen. U kunt namelijk subsidie
krijgen als u uw loden waterleidingen gaat vervangen. Er geldt een waarschuwing tegen het
gebruik van water uit loden waterleidingen voor het aanmaken van (fles)voeding voor
zuigelingen tot één jaar. Zij lopen een zeer beperkt risico. Voor oudere kinderen en
volwassenen levert lood in drinkwater geen risico's op. Heeft u een huis van voor 1960 en
vermoedt u dat uw huis nog (gedeeltelijk) lodenleidingen heeft dan kunt u voor meer
informatie over saneren, subsidiemogelijkheden en gezondheid contact opnemen met:
Ministerie van VROM
loket sanering lodenleidingen
telefoonnummer (070) 3395107
op werkdagen van 8.30 tot 12.30 uur
internet: www.minvrom.nl
Lood en babyvoeding
Als poedermelk wordt aangemaakt met water
uit een loden waterleiding, krijgt de baby lood binnen. De Gezondheidsraad adviseert bij
aanwezigheid van loden waterleidingen bronwater in plaats van kraanwater te gebruiken voor
de bereiding van flesvoeding. De baby loopt geen risico als het alleen borstvoeding
krijgt. Ook niet als de moeder water drinkt uit loden waterleidingen.
Vrouwen worden eveneens meer getroffen dan
mannen, vooral tijdens een zwangerschap en in de menopauze: het lood vult immers de ruimte
op van de ontbrekende voedingsmineralen. Mensen die lijden aan een tekort aan ijzer,
calcium en zink zijn dus extra vatbaar voor loodintoxicatie.
Sinds het bekend worden van de
schadelijkheid van lood voor het milieu, is het gebruik ervan sterk teruggedrongen. Tot
die tijd waren er legio toepassingen:
* De hoge buigzaamheid maakt lood geschikt
om bij woningbouw kieren te dichten (loodslab). Van deze eigenschap wordt ook
gebruikgemaakt in ramen van glas en lood, waarbij het stukje glas in een loden vatting
opgesloten zit en de loodstrippen aan elkaar gesoldeerd worden.
* In oplaadbare batterijen en accu's wordt lood als elektrode gebruikt.
* In brandstoffen kan loodtetraethyl worden gebruikt als octaan verbeteraar. In de EU is
dat sinds 1999 niet meer toegestaan.
* Lood kan worden toegepast in verf om het beter bestendig te maken tegen weersinvloeden.
Sinds 1990 is dat in de EU niet meer toegestaan. Als pigment werd loodwit (loodoxide) veel
toegepast.
* Legering met tin voor orgelpijpen.
* In de elektronica als soldeerverbinding in een legering met tin en soms ook zilver,
(voorbeeld 60%lood, 38%tin en 2%zilver)
* In de legering Woodsmetaal voor diverse toepassingen.
Langdurige blootstelling aan lood en
loodverbindingen kan hersenbeschadigingen veroorzaken en tot bijvoorbeeld dementie
leiden. Om die reden is het niet meer toegestaan lood te gebruiken voor
waterleidingen.
Blootstelling aan lood verdubbelt
kans op manische depressie en vervijfvoudigt kans op angststoornis
Lead exposure was thought to be a thing of
the past, but it is more common today than most realize. A recent study in the Archives of
General Psychiatry (December issue) found that individuals with lead levels of 2.11 ug/dL
or more had 2.3x greater risk of being diagnosed with Manic Depressive Disorder (MDD) and
had nearly 5x the odds of panic disorder compared with those with lead levels of 0.7 ug/dL
or less.
Blootstelling aan lood tijdens
kindertijd veroorzaakt permanente hersenschade
A study using functional magnetic resonance
imaging (fMRI) to evaluate brain function revealed that adults who were exposed to lead as
children incur permanent brain injury. The results were presented today at the annual
meeting of the Radiological Society of North America (RSNA). "What we have found is
that no region of the brain is spared from lead exposure," said the study's lead
author, Kim Cecil, PhD, imaging scientist at Cincinnati Children's Hospital Medical Center
and professor of radiology and pediatrics at the University of Cincinnati College of
Medicine. "Distinct areas of the brain are affected differently." The study is
part of a large research project called the Cincinnati Lead Study, a long-term lead
exposure study conducted through the Cincinnati Children's Environmental Health Center, a
collaborative research group funded by the National Institute of Environmental Health
Sciences and U.S. Environmental Protection Agency. The Cincinnati Lead Study followed
prenatal and early childhood lead exposure of 376 infants from high-risk areas of
Cincinnati between 1979 and 1987. Over the course of the project, the children underwent
behavioral testing and 23 blood analyses that yielded a mean blood lead level. Lead, a
common and potent poison found in water, soil and lead-based paint, is especially toxic to
children's rapidly developing nervous systems. Homes built before 1950 are most likely to
contain lead-based paint, which can chip and be ingested by children. "Lead exposure
has been associated with diminished IQ, poor academic performance, inability to focus and
increased risk of criminal behavior," Cecil said.
Zelfs lage blootstelling aan lood
heeft invloed op IQ van kinderen
Children exposed to lead at levels now
considered safe scored substantially lower on intelligence tests, according to researchers
who suggest one in every 30 children in the United States suffers harmful effects from the
metal. The study also found an average 5.5-point decline in IQ for every additional
10-microgram increase in blood-lead concentration, said Lanphear, a physician at
Children’s Hospital Medical Center in Cincinnati.
Some red lipsticks contain
unhealthy levels of lead
Earlier this month, the watchdog group
Campaign for Safe Cosmetics found that one-third of the lipsticks in a study of 33 red
lipsticks contained levels of lead exceeding 0.1 parts per million.
Exposure to lead, tobacco smoke
raises risk of ADHD
Children exposed prenatally to tobacco
smoke and during childhood to lead face a particularly high risk for ADHD, according to
research done at Cincinnati Children's Hospital Medical Center. The study estimates that
up to 35 percent of ADHD cases in children between the ages of 8 and 15 could be reduced
by eliminating both of these environmental exposures. This could translate into up to
800,000 children. "Tobacco and lead exposure each have their own important adverse
effect," says Tanya Froehlich, M.D., a physician in the Division of Developmental and
Behavioral Pediatrics at Cincinnati Children's and the study's lead author. "But if
children are exposed to both lead and prenatal tobacco, the combined effect is
synergistic." The study is to be published online Nov. 23 by Pediatrics.
"Although we tend to focus on ADHD treatment rather than prevention, our study
suggests that reducing exposures to environmental toxicants might be an important way to
lower rates of ADHD," says Robert Kahn, MD, MPH., a physician and researcher at
Cincinnati Children's and the study's senior author.
The researchers found that children exposed
prenatally to tobacco smoke were 2.4 times more likely to have ADHD. Those with blood lead
levels in the top third had a 2.3 fold increased likelihood of ADHD, despite levels well
below the Centers for Disease Control action level of 10 micrograms per deciliter. Dr.
Froehlich and her colleagues found the risk of ADHD more than eight times higher for
children exposed to both tobacco and lead compared to unexposed children. The study is
based on data of 8 to 15 years olds gathered between 2001 and 2004 from the National
Health and Nutrition Examination Survey (NHANES) from the National Center for Health
Statistics at the Centers for Disease Control and Prevention. NHANES is a nationally
representative sample of the United State population, designed to collect information
about the health and diet of people in the U.S. Prenatal tobacco exposure was measured by
maternal reports of cigarette use during pregnancy. Lead exposure was assessed using
current blood lead level. Some 8.7 percent of the 3,907 children in the study met
diagnostic criteria for ADHD. The diagnosis for ADHD was based on the Diagnostic and
Statistical Manual for Mental Disorders, Fourth Edition, considered the "gold
standard" for defining specific mental health conditions.
Children's blood lead levels linked
to lower test scores
Exposure to lead in early childhood
significantly contributes to lower performances on end-of-grade (EOG) reading tests among
minority and low-income children, according to researchers at Duke University and North
Carolina Central University. "We found a clear dose-response pattern between lead
exposure and test performance, with the effects becoming more pronounced as you move from
children at the high end to the low end of the test-score curve," said lead
investigator Marie Lynn Miranda, director of the Children's Environmental Health
Initiative (CEHI) at Duke's Nicholas School of the Environment. "Given the higher
average lead exposure experienced by African-American children in the United States, our
results show that lead does in fact explain part of the observed achievement gap that
blacks, children of low socioeconomic status and other disadvantaged groups continue to
exhibit in school performance in the U.S. education system, compared to middle- and
upper-class whites," Miranda said. The study, published online in the peer-reviewed
journal NeuroToxicology, linked data on blood-lead levels from the North Carolina
Childhood Lead Poisoning Prevention Program surveillance registry to EOG reading test
scores for 4th graders in all 100 of the state's counties. Researchers used innovative
methods, including the use of a statistical approach called quantile regression, to
measure the contribution of lead exposure to declining levels in children's EOG scores.
Their analyses revealed that early childhood exposure to lead, the family's poverty status
and parental education all account for test-score declines. On average, exposure to lead
accounts for between 7 percent and 16 percent of the decline, with the larger declines
associated with higher blood-lead levels. By comparison, they found the family's poverty
status, as indicated by enrollment in a free or reduced-price school lunch program,
accounts for 25 percent to 28 percent of EOG declines. And parental education accounts for
the largest portion of the drop in test scores, between 58 percent and 65 percent of the
total. "This demonstrates the particular vulnerabilities of socioeconomically and
environmentally disadvantaged children," said Miranda, an associate professor at the
Nicholas School and Duke Medical School's department of pediatrics. "Children who
experience these cumulative deficits are especially disadvantaged when they enter the
school system." The team's analysis showed that children already at the low end of
the test-score curve were more greatly affected by lead exposure – the greater the
exposure, the greater the impact on their scores. However, downward shifts were also
documented in exposed children at the high end of the EOG curve. This is important, the
study noted, because EOG scores are used to place students into advanced and
intellectually gifted (AIG) programs at schools across the United States. "Our
findings show that even low-level lead exposure can push some children out of the score
range that would make them eligible for these special programs," Miranda said.
"To the extent that low-income and minority children are systematically exposed to
more lead, AIG programs become less economically and racially diverse."
Lead Poisoning in Kids
Lead in bone associated with
increased risk of death from cardiovascular disease in men
Boston, MA -- Growing evidence shows that
exposure to lead in the environment is associated with cardiovascular disease, including
increased risk of hypertension. However, those studies have looked at lead concentrations
in blood, not bone lead, a better indicator of cumulative lead exposure over time. In a
new study, researchers at the Harvard School of Public Health (HSPH) and the University of
Michigan School of Public Health found that bone lead was associated with a higher risk of
death from all causes, particularly from cardiovascular disease. It is the first study to
analyze the association between bone lead and mortality. The study appears online on
September 8, 2009, on the website of the journal Circulation and will appear in a later
print edition. "The findings with bone lead are dramatic. It is the first time we
have had a biomarker of cumulative exposure to lead and the strong findings suggest that,
even in an era when current exposures are low, past exposures to lead represent an
important predictor of cardiovascular death, with important public health implications
worldwide," said Marc Weisskopf, assistant professor of environmental and
occupational epidemiology at HSPH and lead author of the study. Air pollution was the main
source of lead in the environment in recent years, though it has been decreasing since
leaded gasoline was banned in the U.S. in the mid-1990s. Most of the lead circulating in
the body is deposited in bone and remains there for years, unlike blood lead, which has a
half life of about 30 days. Since adverse effects from lead on the cardiovascular system
would be expected to show up over time, the researchers expected that bone lead would be a
better marker of chronic toxicity.
The researchers, led by Weisskopf and
senior author Howard Hu, professor of environmental health, epidemiology and internal
medicine at the University of Michigan School of Public Health, analyzed data from 868
participants in the Department of Veterans Affairs Normative Aging Study, a study of aging
in men that began in 1963. Blood lead and bone lead—analyzed using X-ray
fluorescence—were measured for each of the participants. The results showed that the
risk of death from cardiovascular disease was almost six times higher in men with the
highest levels of bone lead compared to men with the lowest levels. The risk of death from
all causes was 2.5 times higher in men with the highest levels of lead compared to those
with the lowest levels. The results appeared independent of age, smoking, education, race,
alcohol, physical activity, BMI, high density lipoprotein or total cholesterol levels,
hypertension or diabetes. There are a number of mechanisms, such as increased oxidative
stress, by which lead exposure may result in cardiovascular mortality, say the authors.
They also note that, in addition to high blood pressure, exposure to lead has been
associated with widened pulse-pressure (an indicator of arterial stiffening) and heart
disease. Given that bone lead may be a better biomarker of cumulative lead exposure than
blood lead, it may be the best predictor of chronic disease from exposure to lead in the
environment. "In addition to spurring further public health measures to reduce
exposure to lead and to begin monitoring for cumulative exposure, mechanistic and clinical
research is needed to determine if opportunities exist to conduct targeted screening and
treatment that can further reduce the burden of cardiovascular disease for the millions of
adults who have had years of elevated lead exposure in the past," said Hu.
Low lead levels in children can
affect cardiovascular responses to stress
Even low levels of lead found in the blood
during early childhood can adversely affect how the child's cardiovascular system responds
to stress and could possibly lead to hypertension later in life, according to a study from
the State University of New York (SUNY) at Oswego. Lead exposure was associated with an
increase in vascular resistance when the children worked on a stressful computer task.
Vascular resistance is a measure of tension within the blood vessels. Increased vascular
resistance may lead to hypertension if it continues over time. The study also found that
lead exposure was associated with a decrease in circulating aldosterone levels.
Aldosterone is a hormone that helps regulate blood pressure. The study, Lead exposure and
cardiovascular dysregulation in children, was conducted by James A. MacKenzie, Brooks B.
Gump, Kristen Roosa, Kestas Bendinskas and Amy Dumas of the State University of New York,
Oswego; Robert Morgan of Oswego Family Physicians; and Patrick Parsons of the New York
State Department of Health. The researchers will present their findings, which during the
122nd annual meeting of The American Physiological Society (www.the-aps.org/press). The
meeting is part of the Experimental Biology 2009 conference, to take place April 18-22 in
New Orleans.
Ongoing research
In an earlier study with a different group of children, the researchers found that higher
lead levels measured at 2 years of age were associated with an increased vascular response
to stress later in life (average of 9.5 years of age). The present study aimed to
determine whether this association was true when both lead and vascular responses were
measured simultaneously, and if it did, how this happens. The researchers gave 140
children, 9-11 years old, a psychologically stressful computer task. They measured the
children's cardiovascular function, including total peripheral resistance, while they were
at rest and while they performed the stressful task. Total peripheral resistance is a
measure of arterial pressure relative to cardiac output. The researchers compared the
current blood lead levels of the children to their cardiovascular functioning during the
experiment. As with the earlier study, they found that lead levels did correlate to the
children's total peripheral resistance response to the stressful task. The finding is
important because increases in total peripheral resistance may predispose people to
hypertension later in life.
Low lead levels
One of the study's most important findings is that all of the participants had very low
lead levels, well below the 10 micrograms per deciliter that the CDC defines as a level of
concern. The highest lead level for the children in this study was 3.8 micrograms per
deciliter. Children may be exposed to lead-based paint or lead-contaminated dust in their
homes or pick it up from the soil outside. The Centers for Disease Control and Prevention
(CDC) has pushed to minimize or eliminate all childhood exposure to lead. "The
interesting thing was that the levels of lead were all pretty low in the children who
participated," Dr. MacKenzie said. "We're seeing the negative effects at these
low levels." While these are preliminary findings, the issue deserves more study, he
said.
Search for the 'how'
In trying to find an explanation for how lead affects total peripheral resistance, the
researchers found increased sympathetic nervous system activity during rest and,
paradoxically, a depressed sympathetic response during the stressful computer task.
Activation of the sympathetic nervous system produces the "fight or flight"
response, raising the heart rate and constricting the blood vessels, among other things.
Sympathetic nervous system activity is an appropriate response to stress, but can be
harmful if activated for a long time. "We believe lead causes an increase in
sympathetic nervous activity during rest which reduces the body's ability to generate a
response when stress comes along," Dr. MacKenzie said. In essence, the cardiovascular
system is revving all the time, making it harder for the body to increase in sympathetic
nervous system activity when needed. The study also found that serum aldosterone levels go
down with higher lead levels, making it harder for the body to activate the sympathetic
nervous system when needed. Dr. MacKenzie cautioned that the data on aldosterone and
sympathetic activity is still preliminary and may be a focus of future research.
Lead in the blood increases women's
mortality
Lead concentrations in the blood are
associated with an increased risk of death from coronary heart diseases (CHD). A study of
533 American women, published in BioMed Central's open access journal Environmental
Health, has shown that those with blood lead concentrations above 8?g/dL were three times
more likely to die of CHD. Naila Khalil worked with a team of researchers from the
University of Pittsburgh and the University of Maryland to study the effects of lead on
the mortality of a group of 65-87 year old women who had joined an earlier study between
1986 and 1988. These women have been followed ever since and their causes of death
recorded. Khalil said, "Despite population-wide declines in blood lead concentrations
during the past 30 years, environmental lead exposure continues to be a public health
concern. Lead is a toxic metal, and our results add to the existing evidence of adverse
affects of lead on health as seen in an older cohort who experienced greater historic
environmental lead exposure". The average population blood lead concentration in the
most recent US National Health and Nutrition Examination Survey (2001-2002) had declined
to 1.45?g/dL. The women studied in Dr. Khalil's research, however, were alive while lead
was still used in paints, water systems and as a gasoline additive. They had an average
blood concentration of 5.3?g/dL, with some women showing levels as high as 21?g/dL.
According to Khalil, "Women with a blood lead concentration above 8?g/dL had a 73%
increased risk of dying. In particular, blood lead was associated with almost three-fold
risk in CHD mortality". This study shows that environmental toxicants, such as lead,
may account for some of the burden of cardiovascular disease, which is the leading cause
of mortality worldwide. It kills nearly half a million women in the United States every
year, more than the next five causes of death combined and nearly twice as many as all
forms of cancer, including breast cancer. The authors conclude, "While the damage may
already have been done for some older people, it is important that we recognize the harm
that environmental exposure to lead can cause. We must remain vigilant and ensure that
lead pollution is minimized for the sake of future generations' health".
Calcium during pregnancy reduces
harmful blood lead levels
Pregnant women who take high levels of
daily calcium supplements show a marked reduction in lead levels in their blood,
suggesting calcium could play a critical role in reducing fetal and infant exposure. A new
study at the University of Michigan shows that women who take 1,200 milligrams of calcium
daily have up to a 31 percent reduction in lead levels. Women who used lead-glazed
ceramics and those with high bone lead levels showed the largest reductions; the average
reduction was about 11 percent, said Howard Hu, chair of the Department of Environmental
Health Sciences at the School of Public Health. Hu is the principal investigator of the
study and one of the senior authors on the paper, which is available online in
Environmental Health Perspectives, the official journal of the U.S. National Institute for
Environmental Health Sciences. Hu, who is also affiliated with the University of Michigan
School of Medicine, said this is the first known randomized study examining calcium
supplementation on lead levels in pregnant women. "We and others have previously
shown that during pregnancy, mothers can transfer lead from their bones to their unborn --
with significant adverse consequences--making maternal bone lead stores a threat even if
current environmental lead exposures are low," Hu said. "This study demonstrates
that dietary calcium supplementation during pregnancy may constitute a low-cost and
low-risk approach for reducing this threat." Lead exposure is a great concern for
pregnant and lactating women, especially in developing countries where lead exposures have
been high until recently, and for women with occupational exposure. Developing fetuses and
nursing babies are exposed to lead from either current exposures to mothers or from the
mobilization of maternal skeletal lead stores accumulated from prior years of exposure.
Bone lead can stay in the body for decades, so even with minimal environmental exposure,
the fetus or nursing infant can still be at great risk from maternal stores of lead.
Lead exposure during fetal development and
infancy can cause low birth weight or slow weight gain after birth, cognitive defects such
as lower intelligence scores, lower motor and visual skills, or even miscarriage. Damage
from lead exposure and poisoning is usually permanent. "The bottom line is that
obstetricians and pediatricians should consider adding calcium supplementation to the
prenatal vitamins normally recommended in pregnant women, particularly if their patients
have a significant history of environmental or occupational lead exposure," Hu said.
The study showed that reductions in blood lead levels were more evident in the second
trimester at 14 percent than in the third trimester at 8 percent. The most compliant group
of women in the study (those who consumed greater than 75 percent of the assigned 1,200
milligram doses of calcium per day) showed a 24 percent decrease. Women in the most
compliant group who also reported using lead glazed ceramics and had the highest bone lead
levels saw the greatest reduction of 31 percent. Researchers analyzed 557 women recruited
from the Mexican Social Security Institute prenatal clinics, which treat the low to
moderate income population of Mexico City. All were in their first trimester; roughly half
were assigned calcium and half a placebo. This recent study corresponds with a previous
study performed by the same group of investigators showing that 1,200-milligram daily
calcium supplementation during lactation reduced maternal blood lead by 15-20 percent, and
breast milk lead by 5-10 percent. This is the first randomized trial to evaluate the
effect of supplementation during pregnancy, when lead is more easily transferred to the
fetus, Hu said.
Childhood lead exposure is
associated with decreased brain volume in adults
Childhood exposure to lead is associated
with shrinking (“volume loss”) of specific parts of the brain in adulthood,
finds a related study in this week’s PLoS Medicine. Dr Kim Cecil and colleagues
(University of Cincinnati, USA) studied the association between exposure to lead in the
uterus and during early childhood and brain volume in adulthood. Childhood lead exposure
has been linked to various types of brain damage, leading to problems such as abnormal
thinking and behavior. But up until now, researchers have known little about how lead
damages the brain in this way or about which brain regions get damaged by exposure to low
to moderate levels of lead in childhood.
Dr Cecil and colleagues studied adults who
were born in a poor area of Cincinnati during a time when it had a high concentration of
older lead-contaminated housing. They recruited 157 such adults, aged between 15 and 17
years, who agreed to undergo specialized brain scans known as magnetic resonance imaging.
The researchers found that exposure to lead as a child was linked with brain volume loss
in adulthood, especially in men. There was a “dose-response” effect—in
other words, the greatest brain volume loss was seen in participants with the greatest
lead exposure in childhood. The specific regions of the brain involved were those
responsible for organizing actions, decisions, and behaviors (known as “executive
functions”), regulating behaviors, and coordinating fine movements (known as
“fine motor control”).
“This analysis,” say the authors,
“suggests that adverse cognitive and behavioral outcomes may be related to lead's
effect on brain development producing persistent alterations in structure.” In an
expert commentary on this study, Dr David Bellinger (Harvard Medical School, Boston,
USA)—who was uninvolved in the research—says: “the associations observed by
Cecil and colleagues provide a clear warning sign that early lead exposure disrupts brain
development in ways that are likely to be permanent.”
Cecil KM, Brubaker CJ, Adler CM, Dietrich
KN, Altaye M, et al. (2008) Decreased brain volume in adults with childhood lead exposure.
PLoS Med 5(5): e112.
Children more vulnerable to harmful
effects of lead
Contrary to prevailing assumptions,
children are more vulnerable to the harmful effects of lead exposure at the age of 6 than
they are in early childhood, according to a Cincinnati Children’s Hospital Medical
Center study to be presented May 4 at the annual meeting of the Pediatric Academic
Societies in Honolulu. “Although we typically worry about protecting toddlers from
lead exposure, our study shows that parents and pediatricians should be just as, if not
more concerned about lead exposure in school-aged children,” says Richard Hornung,
Dr.P.H., a researcher in the division of general and community pediatrics at Cincinnati
Children’s and the study’s main author. The researchers found that blood lead
concentrations (BPb) at age 6, compared to those at younger ages, are more strongly
associated with IQ and reduced volume of gray matter in the prefrontal cortex of the
brain, which is involved in planning, complex thinking and moderating behavior. Overall,
the children’s average BPb levels peaked at 13.9 micrograms of lead per deciliter of
blood at age 2, then declined to an average of 7.3 micrograms per deciliter by age 6. For
children, however, with the same average blood lead levels through age 6, those who
received more of their exposure at age 6 had substantially greater decrements in
intellectual ability than those more heavily exposed at age 2. “Lead toxicity is
difficult to recognize in a clinical setting, but it can have devastating effects,”
says Bruce Lanphear, M.D., director of the Cincinnati Children’s Environmental Health
Center and the study’s senior author. “We found that children may be
particularly vulnerable to lead exposure just as the child approaches school age, during a
period of rapid cognitive development. Because IQ tests were not administered to children
older than 6, it is unknown whether older children are even more vulnerable to
environmental lead exposure, according to Dr. Hornung. Approximately 310,000 U.S. children
age 1 to 5 years have blood lead levels greater than 10 micrograms per deciliter, the
level at which the Centers for Disease Control and Prevention recommends public health
actions be initiated. But research has consistently shown that blood lead levels
considerably lower than 10 micrograms per deciliter are associated with adverse effects.
Federal and state regulatory standards have helped to minimize or eliminate the amount of
lead in U.S. consumer products and occupational settings, according to the National
Institute of Environmental Health Sciences (NIEHS). Today, the most common sources of lead
exposure in the United States are lead-based paint in older homes, contaminated soil,
household dust, drinking water, lead crystal and lead-glazed pottery. While extreme lead
exposure can cause a variety of neurological disorders, such as lack of muscular
coordination, convulsions and coma, lower lead levels have been associated with measurable
deficits in children’s mental development and behavioral problems. These include
hyperactivity, or ADHD, lowered performance on intelligence tests, and deficits in fine
motor function, hand-eye coordination and reaction time. Chronic lead exposure in adults
can result in increased blood pressure, decreased fertility, cataracts, nerve disorders,
muscle and joint pain as well as problems with memory or concentration.
Expert at UH adds obesity to side
effects of lead exposure
Optometry professor finds unexpected link
between prenatal lead exposure and obesity in males. Scientists know exposure to low
levels of lead can result in learning disabilities, hearing loss, language impairments and
vision loss, but a newly discovered side effect may be adult-onset obesity in men,
according to a University of Houston professor. Ronald Fox, a UH professor of vision
sciences, biology and biochemistry, and pharmacology, uncovered the link between lead
exposure and obesity while studying the effects of lead on the retina in mice. Fox found
this more subtle side effect was due to exposure to lead while in the womb, unlike the
rash of reports of children becoming sick from ingesting lead-based toys.To reach his
conclusions, Fox and collaborator Leigh Leasure, an assistant professor of psychology with
UH, undertook an 18-month case study exposing pregnant mice to varying levels of lead in
their drinking water to observe the effects on the offspring. By adding obesity to the
already lengthy list of lead exposure side effects, Fox hopes the Center for Disease
Control and Prevention (CDC) will lower the acceptable lead exposure rate for pregnant
women and children. “The CDC states that the acceptable low-level exposure amount is
equal or less than 10 micrograms per deciliter of blood for mothers or children,” Fox
said. “The acceptable level used to be at 80 micrograms in 1972, but in the 1980s, it
dropped to 60. There’s a push among scientists to drop it down to five, three or two
micrograms per deciliter. “For our experiment, we exposed the pregnant mice and, by
extension, their babies to varying levels of lead through their drinking water,” Fox
said. What happened with the mice surprised Fox and his team. Initially, the prenatally
exposed mice were developing at the same rate as their control counterparts, but at one
year, some startling changes began to occur. “These animals were slower, less
coordinated and fatter at a year old,” Fox said. “Mice exposed to 10 micrograms
– the CDC standard for acceptable exposure – gained about 25 percent more weight
than their control counterparts.” A 1-year-old male mouse is the equivalent of a 30-
to 40-year-old man, he said. But what surprised Fox and his team even more was that the
obesity side effect was strictly limited to the male mice. “We don’t know if the
weight gain was related to testosterone or other hormones, but we’re trying to figure
out why females weren’t affected,” Fox said. Humans can encounter lead exposure
through the soil, dust, air, water, paint and toys, and because lead accumulates in the
body, even minimal lead exposure can have long-lasting effects, according to Fox.
Fox’s results will be published in Environmental Health Perspectives in March, but he
will continue studying the effects of lead in mothers and their offspring.
Lead-Poisoned Kids May Still Be
Unsafe After Relocating
In Chinas Shaanxi province—where
hundreds of children were sickened by lead poisoning from a local factory—families
may still be at risk. According to state media, more than 80 percent of kids in two
villages nearby the smelting plant have dangerously high levels of lead in their blood.
Jefferson neuroscientists find
early lead exposure impedes recovery from brain injury
Exposure to lead can hinder the
brain’s ability to recover from injury, a recent study in laboratory animals shows.
The results have implications for the effects of environmental lead exposure on brain
injuries such as stroke, say researchers at Jefferson Medical College, who led the work.
Lead exposure early in life is known to increase the risk for cancer, renal disease,
hypertension and cardiovascular disease later in life, and as a result, also increases the
risk for stroke and brain damage. Jay Schneider, Ph.D., professor of Pathology, Anatomy
and Cell Biology and Neurology at Jefferson Medical College of Thomas Jefferson University
in Philadelphia and postdoctoral fellow Emmanuel Decamp, Ph.D., wanted to know if it was
possible that lead might alter the potential for plasticity, the ability of the brain to
compensate for an injury. They studied young rats that were fed a diet supplemented with
lead and compared them to others on a diet without lead. In earlier work in the lab, they
found that even brief exposures to lead affected neurotrophic factors in the brain
important for growth and maintenance of neurons and their connections. They ran each group
through some simple behavioral tests before causing a small stroke in a specific part of
the brain that affected a hind limb. Reporting in the journal NeuroToxicology, Dr.
Schneider, who is director of the Parkinson’s Disease Research Unit at Thomas
Jefferson University, and his group saw significant recovery after a brief period of time
in the control group, “as compensatory processes take over,” though the limb
function was not completely back to normal.
“In contrast, those animals that were
exposed to lead earlier in life had worse outcomes in the same period after the
stroke,” he says. “There was significant difference in the brain’s ability
to compensate for that injury.” Because the study was brief, he says, they don’t
know if in a longer period of time the lead-exposed animals would catch up in their
recovery to the controls. There was some recovery in the lead group, but then it leveled
off. The control group continued to get better. “That’s one of the questions we
would like to pursue in further studies – whether lead exposure slows or attenuates
the recovery process after a brain injury,” Dr. Schneider notes. “Have they
recovered as much as they will recover or given more time, would they recover to the same
extent" Is lead exposure affecting the rate of recovery or the recovery
potential"” According to Dr. Schneider, it is well known that lead exposure had
detrimental effects on learning and memory, other forms of brain plasticity. “Brain
plasticity generally refers to the brain’s ability to be molded by experience as well
as its ability to reorganize anatomically and functionally and recover from injury,”
Dr. Schneider says. “It’s why people who have relatively small strokes can
recover function. The brain has an innate ability to reorganize and repair itself. Our
data suggest that lead exposure may compromise or alter this capacity for remodeling that
may impair recovery of function following brain injury.” Next, the group would also
like to see if such a trend translates to recovery from other types of injury, such as
traumatic brain injury. They would also like to explore the notion that childhood lead
exposure increases the risk of a child having a poorer outcome from an acquired brain
injury. Dr. Schneider explains that one important aspect of lead poisoning is impairment
of plasticity. “The data we have begin to support that,” he says. “We want
to look at the effects of different levels of lead exposure on the outcome from acquired
brain injury and see how different types and extents of exposures correspond with the
expression of injury and recovery of function. Then, we want to try to nail down the
biological processes responsible.”
Even minute levels of lead cause
brain damage in children
Even very small amounts of lead in
children's blood -- amounts well below the current federal standard -- are associated with
reduced IQ scores, finds a new six-year Cornell study. The study examined the effect of
lead exposure on cognitive function in children whose blood-lead levels (BLLs) were below
the Centers for Disease Control and Prevention (CDC) standard of 10 micrograms per
deciliter (mcg/dl) -- about 100 parts per billion. The researchers compared children whose
BLLs were between 0 and 5 mcg/dl with children in the 5-10 mcg/dl range. "Even after
taking into consideration family and environmental factors known to affect a child's
cognitive performance, blood lead played a significant role in predicting nonverbal IQ
scores," says Richard Canfield, a senior researcher in Cornell's Division of
Nutritional Sciences and senior author of the study in the journal Environmental Health
Perspectives. "We found that the average IQ scores of children with BLLs of only 5 to
10 mcg/dl were about 5 points lower than the IQ scores of children with BLLs less than 5
mcg/dl. This indicates an adverse effect on children who have a BLL substantially below
the CDC standard, suggesting the need for more stringent regulations," he said. In
the United States over the last several months, nearly 50 specific products, including
millions of toys for young children, have been recalled due to excessive lead in the
paint, plastics and metal. "Our findings emphasize the very real dangers associated
with low-level exposures, to which lead in toys can contribute," Canfield said.
U.S. children are exposed to lead primarily
from household dust contaminated by deteriorating interior lead-based paint. In addition
to toys, other potential sources include contaminated soil, imported food stored in
lead-glazed pottery and certain plastic, metallic and painted products. This most recent
finding builds on the same research team's influential 2003 study, published in the New
England Journal of Medicine, that reported adverse effects of BLLs below 10 mcg/dl in a
group of children followed from infancy to age 5. "Our new findings are based on
follow-up testing of the same children at age 6, using a more comprehensive IQ test to
assess cognitive function. The results provide compelling evidence that low-level lead
exposure has effects into the school-age years," said Todd Jusko '01, a University of
Washington Ph.D. candidate in epidemiology and co-author on both reports.
"Children living in poverty
disproportionately suffer from elevated BLLs," said statistician and co-author
Charles Henderson, a Cornell senior researcher in human development. He also noted that
"even a small decline in an IQ score is likely to be reflected in aptitude test
scores such as the SAT." According to the CDC, about one out of every 50 children in
the United States between ages 1 and 5 has a BLL above 10 mcg/dl and about 10 percent of
children have BLLs of 5 mcg/dl or higher; about 25 percent of U.S. homes with children
under age 6 have a lead-based paint hazard. "The bottom line," according to
Canfield, "is that lead is a persistent neurotoxin that causes brain damage. The fact
that lead has been found in millions of toys, even toys specifically designed for children
to put into their mouths, presents an unacceptable risk. Our findings suggest the need to
re-evaluate the current federal standards for lead in consumer products and the current
definition of an elevated BLL in children."
Safe' blood lead levels linked to
risk of death
Blood lead levels generally considered safe
may be associated with an increased risk of death from many causes, including
cardiovascular disease and stroke, according to a report in Circulation: Journal of the
American Heart Association. Researchers studied lead levels below 10 micrograms per
deciliter (µg/dL) which previously has been considered safe. The levels studied are
common and considerably lower than lead levels perceived by the government as a concern to
public health, said Paul Muntner, Ph.D., author of the study and an associate professor of
epidemiology and medicine at Tulane University School of Public Health and Tropical
Medicine in New Orleans. "Our study found the association of blood lead with
cardiovascular death to be evident at levels as low as 2 ìg/dL," he said.
"Since 38 percent of U.S. adults had lead levels above 2 ìg/dL in 1999–2002,
the public health implications of these findings are substantial." The Occupational
Safety and Health Administration (OSHA) defines high blood lead in adults as higher than
40 µg/dL. The Centers for Disease Control and Prevention recommend that women of
child-bearing age have blood lead levels below 10 µg/dL. Researchers said the study
questions the current belief about what lead levels are safe in the population. "We
wanted to know whether there was an association between the current blood lead levels
among U.S. adults and coronary heart disease, stroke or cancer," Muntner said. Since
the mid-1970s, when lead was no longer added to gasoline or household paint and lead was
banned for use in soldering food cans, average blood lead levels in American adults have
decreased from 13.1 µg/dL to 1.6 µg/dL. "Even though lead levels are much lower
than before, the current levels are still orders of magnitude higher than pre-industrial
levels," Muntner said. Today lead is mostly used to make batteries. It is also used
to make ammunition (bullets), pipes and roofing materials. According to OSHA, exposure to
lead can occur in at least 120 occupations including lead smelting, battery manufacturing,
ship building/repair, auto manufacturing and printing. Breathing contaminated air, eating
contaminated food or soil, or drinking contaminated water are ways people can be exposed
to lead. Inhalation of airborne lead is generally the most significant source of
occupational lead absorption. The researchers used data from the Third National Health and
Nutrition Examination Survey Mortality Follow-Up Study, involving 13,946 adults whose
blood lead levels were collected and measured between 1988 and 1994. When researchers
studied those who died by Dec. 31, 2000, they found that death from any cause,
cardiovascular disease, heart attack and stroke increased progressively at higher lead
levels. Compared to participants with blood lead below 1.9 µg/dL, participants with blood
lead between 3.6 µg/dL and 10 µg/dL had:
* a 25 percent higher risk of death from
any cause
* a 55 percent higher risk of death from cardiovascular diseases
* an 89 percent higher risk of death from heart attack
* two and a half times the risk of death from stroke
"The increased risk of all-cause and
cardiovascular deaths with increased lead levels affected all groups we studied:
non-Hispanic whites, non-Hispanic blacks and Mexican Americans, as well as males and
females," Muntner said. "The risk of death from cancer did not increase at the
blood lead levels that our study investigated. "Our study had limited ability to
evaluate the risks of lead exposure associated with blood lead levels below 2 µg/dL.
Future research is needed to identify the level of lead exposure that is not associated
with major health outcomes. Although markedly reduced, the current blood lead levels may
not be low enough, and we believe that practical and cost-effective methods for reducing
lead exposure in the general U.S. population are needed."
Long-term lead exposure linked to
cognitive decline in older adults
Older adults exposed to high levels of lead
before the 1980s are showing signs of cognitive decrements as a result of long-term lead
exposure in their communities, according to a study published in the online edition of
Neurology, the scientific journal of the American Academy of Neurology. The study involved
985 adults randomly selected throughout the city of Baltimore, Maryland. The participants
were between the ages of 50 and 70 years old and had been exposed to higher levels of lead
prior to the 1980s when lead had been used extensively in commercial products. In
determining the association between high levels of lead and lower cognitive performance,
researchers tested the amount of lead in the tibia, or shinbone, since lead accumulates in
bone. Participants also performed 20 cognitive tests to measure language, processing
speed, eye-hand coordination, executive functioning, verbal memory and learning, and
visual memory. The study found higher tibia lead levels were consistently associated with
worse cognitive performance on tests. "The analysis showed the effect of community
lead exposure was equivalent to two to six years of aging," said principal
investigator Brian Schwartz, MD, with Johns Hopkins Bloomberg School of Public Health in
Baltimore. "If lead is associated with lower cognitive performance, this may suggest
possible treatment and prevention options for older adults." In addition, the study
found tibia lead levels were significantly higher in African Americans compared to
Caucasians. Researchers say the difference likely represents the long-term higher
environmental lead exposures sustained by African Americans in the United States, but
could also be due to different bone mineral densities in African Americans compared to
Caucasians.
Study links lead exposure to brain
cancer in adults
People who are routinely exposed to lead on
the job are 50 percent more likely to die from brain cancer than people who are not
exposed, according to a University of Rochester Medical Center study. More than 18,000
brain and spinal cord tumors will be diagnosed in the United States this year. Yet little
is known about what causes brain cancer; the only established risk factor is radiation,
according to the American Cancer Society. Results of other studies attempting to show a
clear link between lead and cancer have been inconclusive. The new data, based on
information from the U.S. Census Bureau and the National Death Index, may be the largest
study ever to find a lead-cancer link. In doing so it provides further evidence that
widespread environmental risk factors such as lead must be explored, said study author
Edwin van Wijngaarden, Ph.D. "If we are able to help explain the cause of even 1 or 2
percent of the total number of cases, that's important," said van Wijngaarden, an
assistant professor and epidemiologist in the Department of Community and Preventive
Medicine at the University of Rochester. Published in the Sept. 1, 2006, issue of the
International Journal of Cancer, the study computed the risk estimates for lead exposure
and brain cancer from a census sample of 317,968 people who reported their occupations
between 1979 and 1981. Van Wijngaarden was looking for evidence of an exposure-response
trend, or a rise in cancer incidence or mortality associated with an exposure to a toxic
substance. The goal among researchers who do this type of investigation is to identify
preventable, environmental risk factors that might cause the gene mutations that lead to
cancer.
Each occupation was classified into
categories established by the National Cancer Institute. The NCI job matrix for lead is
designed to estimate the likelihood of exposure and the intensity of exposure. It rates
each occupation on a scale from zero (no exposure) to three (high exposure). Gas station
attendants from the 1970s and early 1980s, for example, were estimated to have a high
probability of exposure, but only medium intensity of exposure because their direct
contact with leaded gasoline was not as great as the potential for contact. The jobs with
the highest probability and intensity of lead exposure were painters and automobile
mechanics. But firefighters, engineers, automobile assemblers, truck drivers, plumbers,
welders, and printers or typesetters were all among those individuals with some likelihood
of lead exposure, according to the NCI matrix. When Van Wijngaarden applied the matrix to
nearly 318,000 people and followed their cancer rates for nine years, he found 119 brain
cancer deaths. The death rate among people with jobs that potentially exposed them to lead
was 50 percent higher than unexposed people, and the number of deaths was larger than in
many previous studies, van Wijngaarden said. Other trends that emerged were slightly
higher death rates among less educated and married individuals. Scientists have suspected
for years that lead is a carcinogen, which passes through the blood-brain barrier, making
the brain especially sensitive to the toxic effects of lead. Van Wijngaarden is continuing
his research with a pilot study to measure the actual bone-lead levels in people who have
been diagnosed with brain tumors. "My interest is in exploring the long-term
implications of lead exposure," van Wijngaarden said. "Lately, a lot of the
information about lead and its toxicity has focused on children. We do know that in young
people it can cause acute illness and behavioral problems. But what is under appreciated,
I believe, are the chronic health effects."
Growing body of research links lead
to osteoporosis
Bolstered by recent laboratory findings,
researchers at the University of Rochester Medical Center are embarking on a National
Institutes of Health-funded clinical study to better understand the deceptive role
environmental lead exposure plays in bone maturation and loss. The clinical trial is the
latest in a growing body of research that is putting yet one more notch in the belt of
diseases attributed to lead, and this time, researchers say, its target is older adults at
risk for osteoporosis. For decades, scientists have known that the human skeleton is a
repository for lead in people who were exposed to high levels of this environmental toxin
in their childhood, but thought this storage to be benign. Recently, a growing body of
research is showing that the opposite is true, and that lead in bone actually sets off a
bizarre chain reaction, first accelerating bone growth, and then eventually limiting it so
that a high peak bone mass is not achieved. Preventing a high peak bone mass will
predispose a young person to osteoporosis later in life. Now, researchers in the Center
for Musculoskeletal Research at the University of Rochester Medical Center are set to
embark on the next phase of a four-year, $5 million research project funded by the
National Institute of Environmental Health Sciences with a clinical study aimed at better
understanding the deceptive role lead initially plays in bone development, growth and loss
– and how this all might lead to earlier onset of osteoporosis in those exposed to
high levels of lead as a child. A metabolic bone disease that predominantly occurs in
women, osteoporosis affects one in three American women over the age of 65. It is
characterized by low bone mass that eventually leads to fractures, mostly of the hip and
vertebrae. These fractures can be life-threatening; experts say that more women die each
year from hip fracture complications than from cancer of the ovaries, cervix and uterus
combined. Close to $20 billion dollars is spent each year treating osteoporosis and
related fractures.
An Ironic Growth Pattern
The pattern of growth in the skeleton
determines the peak skeletal density of an individual, and this level is established by
the time most people reach 20. Recent research completed at the University of Rochester
Medical Center shows that lead adversely affects the normal maturation of the growth plate
– but does so in an odd way. "As a child, lead appears to accelerate bone
development and maturation, so that lead-exposed children actually have a higher bone
density than those not exposed to environmental lead," said James Campbell, M.D.,
M.P.H., associate professor of Pediatrics and a co-investigator of the study. "But,
we believe this higher bone density effect is short-lived, and in fact, we believe it
actually prevents these children from achieving an optimal peak bone mass later on in
life." J. Edward Puzas, Ph.D., professor of Orthopaedics and director of the overall
project, added that limiting peak bone mass has dire consequences as a person begins to
age. "When everyone begins to lose bone mass starting at around age 50,
lead-exposed individuals are at a higher risk for bone fractures and osteoporosis –
and probably at an earlier age than the typical osteoporosis patient." At what
specific age lead-exposed individuals will plateau in bone growth, and at what age they
will begin to lose more bone as older adults, is the focus of this clinical research.
Puzas and Campbell have used their prior research to guesstimate when these two milestones
occur, but are turning to sophisticated lead measurement devices to help them pinpoint
exact timeframes. "We believe that somewhere around age 20, we'll begin to see
low-lead exposed individuals surpass high-lead exposed individuals in bone mass
density," Campbell said. "Then, in the 50 to 60 age group – the age at
which any individuals will begin to experience a natural loss of bone – we expect to
see the high-lead exposed individuals losing more bone sooner."
Your tap water: Will that be leaded
or unleaded?
Lead may pose greater leaching risk than
standard tests show
In critiquing a common safety standard for brass used in plumbing, researchers have found
the regimen may be flawed. As a result, they say, some of the lead that crept into tap
water in Washington, D.C., and other metropolitan areas may be traceable to household
fixtures, valves and other components and not just pipes and systems further from the
home. The new study looked at the American National Standards Institute/National
Sanitation Foundation 61 Section 8 standard--a protocol consisting of specific methods and
test-water formulas that governments and industries have relied upon to ensure safe
plumbing since 1988.
"As a result of problems identified
with the test protocol, some products passing National Sanitation Foundation Section 8 may
have a greater capacity to leach lead into water than we believed," said Marc Edwards
of Virginia Tech, who is one of the study leaders. Edwards, Abhijeet Dudi and Nestor
Murray, all at Virginia Tech, and Michael Schock, of the Environmental Protection Agency
(EPA) National Risk Management Research Laboratory, report their findings in the Aug. 4
issue of the Journal of the American Waterworks Association. Edwards, Dudi and Murray are
members of a multidisciplinary team supported by a National Science Foundation Materials
Use: Science, Engineering and Society (MUSES) award. The researchers tested identical
brass devices purchased from a local hardware store by subjecting the pieces to the
Section 8 protocol and to modifications they made to the protocol. They also applied the
same tests to a simulated plumbing device made of solid lead. The results: The Section 8
water samples reacted less, or were less "aggressive," with lead in the plumbing
than designers of the standard had intended. The researchers found other problems that
stemmed from calculations that underlie some of the test results. Normalization factors
allow evaluators to estimate actual lead concentrations at the tap, but they are affected
by device size. Because of normalization and the non-aggressive waters, the small,
simulated device made of pure lead pipe passed the Section 8 leaching test. The scientists
began to scrutinize the Section 8 methods after learning that one of the test solutions
contains high concentrations of orthophosphate to buffer the water's pH. Water utilities
use orthophosphate actually to inhibit lead leaching. So, test solutions containing such
leaching inhibitors could not react adequately with plumbing and would produce a flawed
reading.
"It's analogous to an automobile crash
test using a wall of pillows," Edwards said. Because lead softens alloys, it is an
important component in many plumbing metals. Without adding small quantities of lead,
manufacturers could not craft intricate shapes necessary for modern devices. Under certain
chemical conditions, such as high acidity or low amounts of carbon dissolved from
minerals, the devices can leach significant amounts of that lead into water. The problem
is complex because treatments necessary to treat one water-quality problem, such as
bacteria, can have unintended consequences, such as lead leaching. In the 1986 Safe
Drinking Water Act as amended in 1996 (USEPA, 2000), Congress explicitly banned new
devices containing pure lead pipe, leaded solders, and brass with more than 8 percent lead
content. However, these materials remain installed in older homes. At the time of the
legislation, there were no alternatives for leaded brass, and experts believed it was not
feasible to reduce lead content in devices to that in pipes and solder. Some components
are labeled lead-free, even if they contain 7.99 percent lead. Despite such labeling, all
brass products that contain lead must pass the Section 8 performance-testing standard.
Recently, legislators have proposed updated laws to allow for modern brass alloys--some
containing as little as 0.02 percent lead or less by weight--which could reduce lead
leaching considerably .
New study links lead exposure with
increased risk of cataract
Results from a new study show that lifetime
lead exposure may increase the risk of developing cataracts. Researchers found that men
with high levels of lead in the tibia, the larger of the two leg bones below the knee, had
a 2.5-fold increased risk for cataract, the leading cause of blindness and visual
impairment. "These results suggest that reducing exposure of the public to lead and
lead compounds could lead to a significant decrease in the overall incidence of
cataract," said Kenneth Olden, Ph.D., director of the National Institute of
Environmental Health Sciences. The National Institute of Environmental Health Sciences,
one of the National Institutes of Health, provided support to researchers at the Harvard
School of Public Health and Brigham and Women's Hospital for the nine-year study, which is
also focusing on lead's contribution to hypertension and impairment of kidney and
cognitive function. The findings on risk of cataract are published in the December 8th
issue of the Journal of the American Medical Association. Lead is found in lead-based
paint, contaminated soil, household dust, drinking water, lead crystal, and lead-glazed
pottery. Following exposure to lead, the compound circulates in the bloodstream and
eventually concentrates in the bone. The Harvard researchers tested whether bone lead
levels measured in both the tibia and patella, also known as the kneecap, were associated
with cataract in an ongoing study of men taken from the Boston area. "Given the
strong association between tibia lead and cataract in men, we estimate that lead exposure
plays a significant role in approximately 42 percent of all cataracts in this
population," said Debra Schaumberg, Sc.D., assistant professor of medicine and
ophthalmology at Harvard Medical School and lead author of the study. "While lead in
both the tibia and patella was associated with an increased risk of cataract, tibia lead
was the best predictor of cataract in the study sample."
According to Schaumberg, cataracts develop
as a result of cumulative injury to the crystalline lens of the eye. "Lead can enter
the lens, resulting in gradual injury to certain proteins present in the epithelial cells,
and this eventually results in a cataract," she said. The Harvard researchers are
among the first to use bone lead in studying the effect of lifetime lead exposure on
disease risk. "The best biological marker for estimating a person's cumulative
exposure to lead is provided by skeletal lead," said Dr. Howard Hu, professor of
occupational and environmental medicine at the Harvard School of Public Health and
co-author of the study. "Since blood lead levels reflect only recent exposures, they
are not likely to predict the development of age-related diseases such as cataract, which
take many years to develop." Cataracts, a clouding of the lens resulting in a partial
loss of vision, are very common in older people. By age 80, more than half of all
Americans either have a cataract or have had cataract surgery. Other risk factors for
cataract include diabetes, smoking, long-term alcohol consumption, and prolonged exposure
to ultraviolet sunlight. The prevention of age-related cataract remains an important
public health goal," said Schaumberg. "In addition to the obvious problems of
reduced vision, the visual disability associated with cataracts can have a significant
impact on the risk of falls, fractures, quality of life, and possibly even
mortality."
'Safe' lead levels pose risk to
children's cognitive functioning
ITHACA, N.Y. -- A five-year study has found
that lead is harmful to children at concentrations in the blood that are typically
considered safe.
Reporting in the latest issue (April 17) of
The New England Journal of Medicine , two Cornell University scientists say that children
suffer intellectual impairment at a blood-lead concentration below the level of 10
micrograms per deciliter (mcg/dl) -- about 100 parts per billion -- currently considered
acceptable by the Centers for Disease Control and Prevention (CDC). "We also found
that the amount of impairment attributed to lead was most pronounced at lower
levels," says Richard Canfield, lead author of the journal paper and a senior
researcher in Cornell's Division of Nutritional Sciences.
The study followed 172 children in the
Rochester, N.Y., area whose blood lead was assessed at 6, 12, 18, 24, 36, 48 and 60 months
and who were tested for IQ at both 3 and 5 years of age. The study was conducted by
researchers at Cornell, the Cincinnati Children's Hospital, the University of Rochester,
the National Institutes of Health and the University of Washington.
Before 1970, childhood lead poisoning was
defined by a blood-lead concentration greater than 60 mcg/dl. The level considered
acceptable was set at 40 mcg/dl in 1970 and reduced to 25 mcg/dl in 1985. The current
level of 10 mcg/dl was established in 1991 based on findings linking lead at this level to
lowered intelligence and diminished school performance.
An important feature of the study is its
focus on children with blood-lead levels below 10 mcg/dl. Most previous research examined
the effects of lead in the 10 to 30 mcg/dl range. But the new study finds lead-related
impairments at lower levels.
"In our sample, most of the damage to
intellectual functioning occurs at blood-lead concentrations that are below 10
mcg/dl," says Canfield. The amount of impairment was also much greater than the
researchers had expected. "Given the relatively low exposure levels, we were
surprised to find that the IQ scores of children with blood-lead levels of 10 mcg/dl were
about 7 points lower than for children with lead levels of 1 mcg/dl," Canfield
says.At the same time, the study found that an increase in blood lead from 10 to 30 mcg/dl
is associated with only a small additional decline in IQ of about 2 to 3 points.
"Because most prior research focused on children with higher exposures than in our
sample, we suspect those investigators could estimate only the damage that occurs after
blood lead has reached 10 mcg/dl -- unaware that substantial impairment may occur at lower
levels," says Charles Henderson, a senior researcher in the Department of Human
Development at Cornell and se! cond author of the paper.
"While these findings are based on a
single sample and will need to be replicated in further studies," says Henderson,
"we found that the relation between lead and IQ was very consistent at 3 and 5 years
of age." He notes that the researchers controlled for maternal education, IQ, income,
prenatal exposure to tobacco and level of intellectual stimulation in the home.
Children's blood-lead concentrations have
fallen by more than 80 percent in the past 30 years, but Canfield notes that undue lead
exposure is an especially important problem among children living in impoverished
communities. For example, the CDC recently reported that children ages 1 to 5 years who
were enrolled in Medicaid accounted for 60 percent of all U.S. children with blood-lead
levels greater than 10 mcg/dl. Furthermore, more than 80 percent of children enrolled in
Medicaid do not typically receive blood-lead tests. Many such children live in housing
built before about 1950, which is more likely to contain paint having high levels of lead.
If the paint cracks or peels, lead particles can fall onto floors and onto children's
toys. Children ingest the lead particles when they put contaminated toys and fingers into
their mouths.
According to new CDC figures, approximately
1 out of every 50 children in the United States between the ages of 1 and 5 years has a
blood-lead level above 10 mcg/dl, whereas 1 in every 10 children has blood-lead levels of
5 mcg/dl or higher. "Given the current CDC recommendations and the findings from our
study, it appears that many children are passing their lead test but failing to escape the
adverse consequences of low-level lead exposure," Canfield says.
Study shows how eye cells die when
exposed to lead
UH research suggests possible therapies for
eye disorders, injury
A new study designed to find out why cells
in the eye die when exposed to lead may provide novel therapies for retinal damage caused
by injury or diseases such as diabetes and retinitis pigmentosa.
The study, published in the Feb. 4 issue of
the Proceedings of the National Academy of Sciences, focused on identifying how low-level
lead exposure during development in mice injures and eventually kills rod-shaped
photoreceptor cells, or rods, in the eye.
Rods are cells in the eye that help humans
see in dim light. The other type of photoreceptors, or light-gathering cells, called cones
are responsible for color and spatial vision. Cones are used primarily in daylight and for
activities such as reading.
"Lead is a toxicant, and when the
retina is exposed to lead, we found that it triggers a chain of biochemical events that
leads to the selective apoptotic death of rod photoreceptors," says Donald A. Fox,
professor of vision sciences, biology and biochemistry, and pharmacology at the University
of Houston and principal investigator of the study.
"The human eye contains so many rods
that you can lose about 20 percent of them and not have much functional loss of
vision," Fox says. "But for people who need to see clearly at night, such as
truck drivers, or for people who are losing their rods due to disease or injury, finding a
way to prevent the rods from dying is important."
In June 2002, Fox and his colleagues
published a study showing that 7- to 10-year-old children whose mothers had elevated
levels of lead in their blood during the first trimester of pregnancy developed retinal
abnormalities, specifically in their rods (Investigative Ophthalmology & Visual
Science, June 2002, Vol. 43. No. 6). A study currently underway with the same children is
assessing whether lead exposure during development affects the eye's cones as well.
"We can't tell whether the rods
actually die, because these are living children, but there are unique functional
abnormalities in these children. They may have visual system deficits that eventually
could lead to permanent retinal alterations and learning problems," Fox says.
"We're not sure what the functional basis of this observation is, and we hope to
study it further."
According to the Centers for Disease
Control and Prevention, the acceptable level of lead in the blood is 10 micrograms per
deciliter. The CDC estimates that about 900,000 U.S. children under age 6 have blood lead
levels at that level or higher. The children in Fox's ongoing study live in and around
Mexico City and had blood lead levels of 6 micrograms per deciliter or above.
Fox's latest animal study in PNAS sheds
some light on the mechanisms responsible for lead-mediated cell death, or apoptosis, in
the eye, and may suggest possible treatment options for patients suffering from various
forms of retinal degeneration.
The key to most cell death is a structure
within each cell called the mitochondrion, which is known primarily as the central
component responsible for generating energy for the cell. But when a cell is damaged, the
mitochondria become the "central executioners," releasing proteins sequestered
within them that are death signals for the cell.
Here's how Fox believes lead-mediated cell
death occurs:
When the rod cells in the eye are exposed
to lead, it triggers an increase in the amount of lead and calcium entering the cell. A
higher level of calcium within the mitochondria sensitizes the mitochondria to interact
with a "death factor" protein produced by the cell called Bax. Fox says Bax
seems to cause channels, or pores, in the mitochondria to open up and release yet another
"death factor" protein called cytochrome c. This protein eventually causes
changes that wreak havoc on the cell's nucleus, destroying its DNA and killing the cell.
"The mitochondrion is like a fort
that's tightly guarded," Fox explains. "Normally things don't get out. But Bax
appears to open up the gate to the fort, letting cytochrome c escape."
Guy Perkins, Fox's colleague at the
National Center for Microscopy and Imaging Research at the University of California, San
Diego, produced detailed images of the animals' rod mitochondria for the study.
"We found the lead-exposed eyes had
more of these 'gates,' which are called contact sites, opened up along the surface of the
mitochondria than the non-exposed eyes, and we believe these contact sites are associated
with the cytochrome c release," Fox says.
The researchers also found that an excess
of an anti-death protein called Bcl-xL completely blocked the death of the eye's rod cells
and maintained normal mitochondrial function in the rods throughout adulthood.
"All cells produce anti-death proteins
like Bcl-xL, and normally when they combine with Bax, it prevents Bax from triggering cell
death. Too much Bax results in cell death," Fox says.
"But these transgenic mice were
genetically engineered to produce excessive amounts of Bcl-xL in their rod cells. We found
that these overexpressed levels of Bcl-xL blocked the Bax from associating with the
mitochondria, as well as blocked the increased formation of contact sites and release of
cytochrome c from the mitochondria. If the cytochrome c can't get out of the mitochondria,
the cells do not die."
The research results suggest possible
avenues for treatment of some eye disorders.
"For people whose rods are dying, such
as in retinitis pigmentosa, or diabetes, or immediately after a traumatic eye injury, if
you can get higher levels of this anti-death protein, Bcl-xL, or one like it, into the
eye, it could help prevent cell death. It has relevance for therapies for a wide variety
of retinal degenerations," Fox says.
The key to Fox's experiment was to expose
the mice to lead levels that are relevant to environmental levels of lead that humans
might be exposed to. "Previous animal models have used lead levels that were not
consistent with the low-level lead exposure and slow cellular degeneration that actually
occurs in human disease," he says.
US researchers find first
conclusive evidence that lead is linked to male infertility
A report in Europe's leading reproductive
medicine journal Human Reproduction[1] concludes that exposure to lead damages sperm
function and may be a contributory cause of unexplained male infertility.[2]
The findings have led principal
investigator Dr Susan Benoff to urge doctors to measure lead in seminal plasma when
evaluating men from couples with unexplained fertility. She also believes there is a case
for health and safety authorities to continue re-evaluating environmental exposure
limits.[3]
Dr Benoff, director of the Fertility
Research Laboratories at the North Shore-Long Island Jewish Research Institute in
Manhasset, New York, and colleagues from several other US institutions, undertook a
prospective, double-blind study of metal ion levels and sperm function in semen from the
partners of 140 consecutive women undergoing their first IVF cycle.
They found that lead levels in seminal
plasma varied over a wide range and there was a significant association between high lead
levels and a low fertilisation rates, with changes in lead levels accounting for a fifth
of the variance in fertilisation rates.
"From our tests on lead in the seminal
plasma of the participants and control experiments on nine fertile donors, we have
evidence that higher lead levels interfere both with the ability of the sperm to bind to
the egg and with its ability to fertilise the egg," said Dr Benoff.
In order to fertilise an egg, a sperm has
first to bind to it. A sugar called mannose on the outer coating of the egg is crucial to
binding. Mannose receptors located on the head of human sperm recognise the mannose on the
coating of the egg and regulate the binding process.
Then the sperm has to penetrate the egg.
Successful binding induces an event called mannose-induced acrosome reaction – the
release of digestive enzymes from the sperm that ease its passage through the egg coating
so that its nucleus can fertilise the egg.
The researchers found that in the 140 men
whose partners were undergoing IVF, higher lead levels in the seminal plasma correlated
with low expression of mannose receptors and with inability of sperm to undergo
mannose-induced acrosome reaction. Conversely, higher lead levels were associated with
premature (or spontaneous) acrosome reaction that occurs before sperm-egg contact, also
blocking fertilisation.
"To see whether this association
between increased lead levels could be causal we exposed healthy sperm from nine fertile
donors to increasing doses of exogenous lead to see what would happen. We got the same
results," said Dr Benoff.
"These biomarkers provide relatively
unambiguous endpoints for lead-induced reproductive toxicity and our data suggest that
lead is acting at multiple levels in testis and sperm to decrease human male fertility.
"Our data also confirm that increased
seminal plasma lead levels can occur without any detectable effects on male reproductive
hormone function and also that they are associated with decreased sperm concentration,
sperm shape, form and movement, suggesting that lead also acts in the testis. Elevated
lead levels in rats' testes are associated with programmed cell death of sperm precursors
and studies of men with non-obstructive low or zero sperm counts indicate that programmed
cell death in the testes is a major determinant of sperm count in the ejaculate. This
leads us to believe that lead is a contributory factor of declining sperm counts."
She said the findings of high seminal lead
levels among the 140 men in the study were unexpected, as lifestyle questionnaires showed
that none was engaged in occupations likely to produce exposure to metal ions. High lead
levels in up to 29 of the IVF patients were associated with smoking and/or alcohol
consumption, but high levels in patients who did not smoke cigarettes or drink alcohol
were unexplained. One possibility was lack of exercise (blood lead levels increase with
decreased physical activity). Another possibility was a low calcium or high lactose or fat
diet, which can enhance lead accumulation. Genetic variation in response to lead exposure
may also be a factor as the study revealed some instances of normal fertilisation rates
despite high lead levels and reduced fertilisation rates despite low lead levels.
Dr Benoff said it was important that the
results should not be construed as evidence of an epidemic of overt lead toxicity as none
of the patients showed signs of lead toxicity and it is not yet known if there is a strong
correlation between seminal plasma lead levels and lead concentration in the blood (the
normal method of measuring lead exposure).
But she warned: "In the light of these
results, environmental exposure limits for lead might be re-evaluated."
She said it was also important that men are
often 'under served' at fertility clinics. "Our findings emphasise the need for
co-operation between reproductive endocrinologists and urologists and a workup of the male
partner of infertile couples that is more extensive than a simple semen analysis or
measurement of circulating reproductive hormones. We suggest the addition of measurements
of the heavy and transition metal ion content of seminal plasma (not blood) and some form
of sperm function testing. It must be recognised that treating the male is generally less
invasive and less costly than treating the female."
International Study Finds Mothers'
Lifetime Lead Exposures May Put Breast-Fed Newborns At Risk
Results from a study conducted jointly by
Australian and American scientists indicate that lead which has accumulated in a woman's
bones from earlier exposures can be released during pregnancy and transferred to breast
milk during lactation. This can translate into increased exposures for breast-fed infants
whose mothers have a long-term history of lead exposure themselves.
The report appears today in the online
version of the October issue of Environmental Health Perspectives, the monthly journal of
the National Institute of Environmental Health Sciences. The study was co-funded by NIEHS
and the National Institutes of Health's Office of Research on Minority Health.
"We should point out that breast
feeding is still an important option for healthy mothers," said Brian Gulson, Ph.D.,
a toxicologist with Macquarie University in Sydney, Australia, and chief investigator for
the project. "What we are saying is that breast-fed infants are only at risk if the
mother has been previously exposed to high concentrations of lead from external sources
such as leaded paint, pottery, or, in many other countries, industrial sources and leaded
gasoline."
While previous research had demonstrated
that lead is stored in bones, scientists could not quantify its release into the blood and
other bodily fluids. To answer that question, the researchers compared second-generation
Australian women with women who had migrated to Australia from Eastern Europe.
Since lead found in Eastern Europe has a
slightly different atomic weight than lead found in Australia, the scientists were able to
differentiate between skeletal lead deposits that had accumulated from the immigrants'
earlier exposures while in their native country, and the lead burden received from more
recent exposures. Hence, any circulating blood lead that matched the "Eastern
European" profile could only be derived from skeletal stores.
Earlier data from the same study had shown
that as much as 40 to 70 percent of the blood lead in pregnant women can come from lead
that has accumulated in the bones. Additional analyses had revealed a significant increase
in the mobilization of maternal skeletal lead during lactation. "Based on these
observations, we wondered whether the infants born to these mothers might be at greater
risk from breast feeding than from formula," said Gulson.
Because the study participants' blood lead
concentrations were relatively low -- most had values less than 5 micrograms lead per
deciliter (100 milliliters) of blood -- the lead concentrations in their breast milk were
also low - 0.7 parts per billion on average. These concentrations were not significantly
different from those found in various kinds of infant formulae.
In spite of these low concentrations, the
researchers found a strong correlation between the amount of lead in the mothers' milk
samples and the corresponding blood lead levels of the infants. In fact, calculations
based on the first 60 to 90 days postpartum indicated that 36 to 80 percent of the
infants' total blood lead was coming from breast milk or formula.
"Our data indicate that lead from
urban air and water where these infants reside contributed negligibly to blood lead, while
soil and dust were not considered to be relevant sources because these infants had not
reached the stage of crawling and ubiquitous hand-to-mouth activity," said Gulson.
"Therefore, we concluded that dietary lead was the primary source contributing to the
body burden observed in these subjects, with a major part of the dietary lead ultimately
derived from the mothers' bones."
The researchers also found a statistical
link between the lead concentration in the maternal cord blood and lead levels in the
first breast milk samples, a finding that could have clinical significance. Bill Jameson,
Ph.D., the Institute toxicologist who serves as NIEHS project officer for the study, said
"If this relationship can be verified through further investigations, then one could
obtain an accurate estimate of an infant's lead exposure by simply testing the mother's
blood lead."
The study also produced preliminary
evidence suggesting that calcium supplementation can have a protective effect by slowing
the release of lead from skeletal stores. The Australian researchers are planning
additional NIEHS-funded studies to determine calcium's effectiveness in pregnant and
nursing mothers.
Maternal Lead Exposure Linked To
High Numbers Of Cavities
Exposure to high amounts of lead is likely
one cause of the high rates of tooth decay found among certain groups, such as children
raised in the inner city, according to a study in rats by University of Rochester dental
researchers published in the September issue of Nature Medicine.
The scientists say that while lead does not
actually cause cavities, it appears to make rats -- and thus people, whose teeth get
cavities in an identical manner -- much more susceptible.
"This is one more compelling reason to
get lead out of the environment," says lead investigator William Bowen, Margaret and
Cy Welcher Professor of Dental Research and the founder of the Rochester Caries Research
Center, the nation's first research center on tooth decay. Also working on the project
were Gene Watson, assistant professor of clinical dentistry; graduate student Bianca
Davis; Richard Raubertas, associate professor of biostatistics; and technician Sylvia
Pearson.
Lead is well recognized as causing
developmental and other problems. While lead has been removed from most gasoline, it's
still present in old paint and commonly in soil or dust around contaminated buildings.
Bowen says that the areas with the highest lead pollution -- inner cities and the
Northeast -- mirror areas where dentists see the highest rates of tooth decay.
The team studied cavity susceptibility in
rats born of mothers exposed to lead compared to offspring of rats not exposed to lead and
found that offspring from exposed rats had 40 percent more cavities. The study, funded by
the National Institute of Dental Research (NIDR), is the first to document the link
between lead exposure and high cavity rates that a few small epidemiological studies have
suggested.
The team is now searching for the cause.
Some studies have suggested that lead interferes with the development of teeth. In humans
lead is stored in the bones for decades, and higher amounts than normal are released into
the blood of women who are pregnant. These high levels reach the fetus at a time critical
to the development of teeth and salivary glands. The scientists discovered another
possibility: They found that pups of exposed rats produced 30 percent less saliva, which
protects teeth against cavities by neutralizing acids, providing minerals, and in many
other ways. In addition, they detected levels of lead in the mothers' milk that were 10
times higher than the lead levels in their blood.
In an accompanying article in the journal,
dentists Martin Curzon and Jack Toumba of the Leeds Dental School in the United Kingdom
say this is the first time that scientists have pinpointed breast milk as a likely route
of lead transfer from mother to offspring, and that reduced saliva flow has been
implicated as a likely mechanism of decay in lead-induced cavities.
"Lead is not something that most
dentists think of when they talk about the causes of cavities, but they should," says
Watson. Poor hygiene, lack of dental care, and poor diet are still major concerns of
dentists, as they should be, says Bowen. But he suggests that dentists who treat children
from areas of high lead pollution should consider boosting standard preventive measures:
fluoride treatments, check-ups, healthy diet, and dental sealants.
Lead is likely one reason why dental
cavities are still a major problem in some pockets of the population despite the
widespread use of fluoride and fluoridated toothpaste, Bowen says. While about half of 12
year olds in the U.S. are now free of cavities, 80 percent of the cavities in the group
are seen in just one-fifth of the children. Ninety-five percent of all adults in the U.S.
have cavities, which are a leading cause of tooth loss.
"There's a feeling among some people
that dental caries is licked, that it's no longer a problem," says Bowen. "The
fact is that it is still a serious public health problem in the U.S. and throughout the
world."
Research shows low lead in body can
cause spontaneous abortion
CHAPEL HILL, N.C. - Medical scientists have
known for decades that high levels of lead in the body often cause spontaneous abortions,
but now a new study shows that lower lead levels can produce that result too.
The risk of spontaneous abortion nearly
doubles for every increase of five micrograms of lead per deciliter of blood, the research
revealed.
Dr. Irva Hertz-Picciotto, professor of
epidemiology at the University of North Carolina at Chapel Hill School of Public Health,
Dr. Victor H. Borja-Aburto of Mexico's National Institute of Public Health and colleagues
conducted the study. A report appears in the Sept. 15 issue of the American Journal of
Epidemiology.
"We did this work because results of
previous studies of low-level lead in pregnant women and spontaneous abortion were
inconclusive," Hertz-Picciotto said. "The earlier research was not designed well
enough to answer the question. This study is the best-designed so far and, we believe,
does answer it. While further work is needed to confirm our results, it does appear that
low to moderate lead can be a problem during pregnancy."
The project took place in Mexico City from
1994 to 1996. Investigators enrolled 668 women, who were interviewed, contributed blood
specimens and were followed through home visits or telephone calls during their
pregnancies. Mexico's respected National Institute of Neurology and Neurosurgery, which
participates in the U.S. Centers for Disease Control and Prevention Blood Lead Proficiency
Testing Program, analyzed the blood samples for lead. Another Mexican laboratory conducted
analyses for signs of infection. Women averaged about 11 micrograms of lead per deciliter
of blood, which is similar to average levels in the United States in the 1970s.
Researchers recorded whose pregnancies
failed and whose did not and compared those records with subjects' blood lead levels.
Thirty-six of 562 subjects still participating at five months gestation already had lost
their babies.
"We did not find many infections that
could cause spontaneous abortions, but we did find a dose response for lead," said
Hertz-Picciotto, also a fellow at UNC-CH's Carolina Population Center. "That means
that the more lead the women had in their systems, the greater the chance that they would
spontaneously abort. The levels of lead in blood in our women were all below the
acceptable standard for occupational exposures."
Most lead that Mexican women absorb comes
from consuming food from ceramic cookware glazed with lead and from air pollution, she
said. Another source may be husbands whose clothes become contaminated at work or whose
semen is contaminated.
Since lead was eliminated from gasoline in
the United States in the 1970s, levels of the toxic metal in U.S. residents have dropped
over the past several decades except in certain subgroups, Hertz-Picciotto said. Among the
chief sources of continued exposure in this country are air and soil pollution, lead-based
paints in older homes and apartments and certain traditional ethnic remedies.
The new study indicates that exposures
comparable to those of the U.S. general population in the 1970s and to many populations
worldwide today can boost the risk of spontaneous abortion, the scientist said.
"These are far lower than exposures
encountered in some occupations," she said.
The Mexican government funded the study.
Scientists consider the research a landmark study since investigators measured blood lead
levels before any pregnancies failed and avoided limitations of earlier work.
Lead at both high and low doses already has
been shown to damage the nervous system and at high doses to injure the kidneys and
reproductive systems, Hertz-Picciotto said. The metal easily crosses the placenta to
developing infants.
Borja-Aburto earned his Ph.D. in
epidemiology at UNC-CH's School of Public Health in 1995 and now directs the National
Center of Environmental Health in Metepec, Mexico.
Vitamin C levels linked to amount
of lead in blood
Despite the 1978 ban on lead-based paint
for residential use, lead poisoning continues to be a serious public health threat,
particularly for children because they are most susceptible to its effects.
In a new observational study, a pair of
researchers at the San Francisco Veterans Affairs Medical Center and the University of
California, San Francisco found that low levels of ascorbic acid (vitamin C) in the blood
stream were associated with high blood levels of lead among Americans. The study's
findings, which are published in the June 23 issue of the Journal of the American Medical
Association (JAMA), also indicate that about half of one percent of all Americans (more
than a million people) have elevated levels of lead in their blood.
According to the US Environmental
Protection Agency, current studies suggest that the primary sources of lead exposure for
most children are deteriorating lead-based paint, lead-contaminated dust, and
lead-contaminated residential soil. Prior to 1978, lead was commonly used as a coloring
agent and a stabilizer in paint.
"Vitamin C levels are an important
independent correlate of blood lead levels among Americans," says Joel Simon, MD,
MPH, SFVAMC staff physician and UCSF assistant professor of medicine, epidemiology &
biostatistics. "To our knowledge, this report is the first population-based study to
establish such an association. If a causal relation is confirmed, increased consumption of
ascorbic acid may have public health implications for the prevention of lead
toxicity."
The correlation between levels of vitamin C
and blood lead levels is supported by the findings of a recent small clinical trial,
conducted at the University of Texas Medical Branch in Galveston, that found that 1000mg
vitamin C supplements decreased the blood lead levels of heavy smokers. Because smoking
decreases the absorption and increases the metabolism of vitamin C, higher dietary vitamin
C intake levels are recommended.
According to Simon, there are no acceptable
levels of lead in humans. Symptoms of acute lead poisoning in adults include loss of
appetite, abdominal pain, renal (kidney) disease, anemia, headache, memory loss, and
peripheral neuropathy (pain, numbness, or tingling of the arms and legs). In children,
signs of acute poisoning are anemia, abdominal pain and nervous system disorders. At
sub-acute levels of lead poisoning, there are often no symptoms, but such levels can cause
mental retardation, loss of cognitive function, language deficits, and behavior problems.
As a preventive measure, Simon recommends
increasing the amount of fresh fruits and vegetables consumed everyday because of their
vitamin C content as well as their many other nutritional benefits. "Humans are one
of the very few mammals that do not produce vitamin C on their own," says Simon,
"so all of it must be obtained from dietary sources." If people are concerned
they are not receiving the proper amount of vitamins in their diets, Simon says a multiple
vitamin or a modest dose vitamin C supplement may be taken as an 'insurance policy.'
The Recommended Daily Allowance (RDA) of
vitamin C for non-smoking adults is 60 mg and 100 mg for smokers. The RDA for children is
45 mg. However, new dietary reference intakes for vitamin C, such as the estimated average
requirement level, are currently being formulated and are likely to be higher. As a point
of reference, a medium size orange contains 60 to 80 mg of vitamin C, and one cup of
freshly squeezed orange juice has about 120 mg of the vitamin.
According to Simon, there are very few
negative effects of too much vitamin C.
However, he says intakes of 1000 mg will
result in saturation of the plasma in the blood stream. Larger intakes are probably not
indicated and are passed from the body in the stool and in urine. Mega-doses of vitamin C
(3000 mg or more) can cause diarrhea and stomach cramps. And while persons with
hemochromatosis, a hereditary iron-storage disorder, should not be discouraged from eating
fresh fruits and vegetables, they should be cautious about consuming supplements
containing more than 500 mg of vitamin C because vitamin C enhances iron absorption and
could worsen this condition.
The investigators studied data gathered by
the Third National Health and Nutrition Examination Survey, 1988-1994 (NHANES III). The
national probability survey of Americans employed a stratified, cluster sampling design.
After excluding some participants because of reported histories of lead poisoning, or
questionable or missing information, the researchers used statistical methods to calculate
their findings. In all, data from more than 19,500 Americans were analyzed.
Lead accelerates aging process
years after exposure
ST. PAUL, MN - Lead exposure on the job can
cause progressive declines in memory and learning abilities nearly two decades later,
according to a study in the October 24 issue of Neurology, the scientific journal of the
American Academy of Neurology.
The study compared 535 former chemical
manufacturing employees exposed to lead at work to 118 non-exposed people from the same
neighborhoods.
"The effects of the average level of
bone lead found in former lead workers was like five more years of aging on the
brain," said Brian Schwartz, MD, of Johns Hopkins School of Hygiene and Public Health
in Baltimore, MD.
The study participants were followed for
four years, undergoing two to four sets of neurological tests with an average of one year
between tests. The former workers had an average of 8 years of occupational exposure to
lead with an average of 16 years since last working with lead.
The first year of the study, lead levels
were determined through blood tests, while follow up visits measured lead levels in bone
through a technique called x-ray fluorescence.
"The higher the peak level of lead
determined in former lead workers, the greater the decline in brain functions,"
Schwartz said. "Since these declines were seen long after exposure to lead had
stopped, it suggests that the effect of lead on the brain is progressive."
The workers not only had greater declines
in test scores due to lead, but also in normal age-related declines in brain functions,
Schwartz said.
Significant differences were discovered
between the former workers and other participants in tests involved in visual
construction, verbal memory and learning, visual memory, planning and organizational
ability, and manual dexterity.
"We know there's a decline in brain
power as we get older -- generally we call this 'normal aging,'" said Schwartz.
"Most of the research has been about how chemicals, like lead, affect kids. This is
the first study to explore long-term problems caused by exposure to chemicals as adults.
Some of what we have been calling 'normal aging' may in fact be due to past exposures to
chemicals or other agents that can affect the central nervous system. This is potentially
a very important health problem."
