Study links pesticide to ADHD in children
Health » More than 1,100 children were tested during a four-year period.
By Thomas H. Maugh Li
Los Angeles Times
Updated: 05/17/2010 07:16:57 AM MDT
Children with higher levels of the pesticide
malathion in their urine seem to be at an
increased risk of attention deficit hyperactivity
disorder, or ADHD, researchers reported today.
Several previous studies have linked
neurodevelopmental and behavioral disorders such
as ADHD to exposure to pesticides, but generally
in children of farmworkers and others exposed to
abnormally high levels of the chemicals.
The new study is the first to focus on “a
population sample more representative of the
United States, and not one selected for being at
high exposure,” said epidemiologist Marc G.
Weisskopf of Harvard University’s School of
Public Health, the senior author of the paper in the journal Pediatrics.
The study is “interesting and provocative …
because the levels of pesticide are very low,”
said epidemiologist Brenda Eskenazi of the
University of California at Berkeley, who was not
involved in the research. “We need to build up a
body of evidence [linking pesticides and
neurobehavioral development] , and we are building it.”
ADHD is thought to affect 3 percent to 7 percent
of children in the United States, with boys
affected much more heavily than girls. Its
prevalence is generally assumed to have increased
sharply in the last three to four decades, but
controversy exists about whether the incidence
has increased or diagnostic standards have broadened.
Weisskopf and his colleagues studied data on
1,139 children from the government’s National
Health and Nutrition Examination Survey for the
period 2000 to 2004. Among the information
collected in the survey were the level of
metabolites of malathion in urine and, through a
structured interview with the parents, whether a
child had been formally diagnosed with ADHD.
There were 119 children diagnosed with ADHD.
Accounting for factors that could confound the
results, the researchers concluded that a tenfold
increase in malathion metabolite levels in urine
— still a very low level — was associated with
a 55 percent higher risk of having ADHD. For the
most commonly detected metabolite, dimethyl
thiophosphate, children with levels higher than
the median of detectable concentrations were
twice as likely to have been diagnosed with ADHD
as those with no detectable concentrations.
Forty organophosphate pesticides similar to
malathion are registered in the United States,
with at least 73 million pounds used in agricultural and residential settings.
Weisskopf and his colleagues speculated that for
most of the children in their study, exposure
came through food. The 2008 report of the U.S.
pesticide residue program found, for example,
that 28 percent of frozen blueberries, 25 percent
of strawberries and 19 percent of celery were contaminated with malathion.
The study has some obvious deficiencies. Unlike
DDT and certain other pesticides, malathion is
cleared from the body quickly, in three to five
days, and levels can fluctuate widely. Because
the government health and nutrition survey is a
“snapshot” of urine levels at one point in time,
it says little about long-term exposures, Weisskopf conceded.
But if the children’s diets remain relatively
constant over a long term, he said, then the
findings are probably a reasonable estimate of
normal levels. Variations in exposure over long
periods would make it harder to find an
association, he added, so the fact that they found a link is significant.
Other researchers are finding similar links
between pesticides and developmental problems.
Epidemiologist Virginia A. Rauh of Columbia
University has been finding links to the
pesticides chlorpyrifos and diazinon and Eskenazi
is seeing similar results with malathion.
“Ideally we would like to get populations with
this level of exposure and follow them over time
to get (causality) correct,” Weisskopf said. But
studies like this one “should raise eyebrows and
get people concerned enough to want to follow up intensively. “
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