Pesticides may increase risk of ADHD in children
■ Children with higher-than-average levels of a common metabolite were twice as likely to have ADHD than were those whose levels were undetectable.
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During consultations for children with attention-deficit/hyperactivity disorder, pediatrician Ari Brown, MD, said physicians should discuss links between pesticide exposure and ADHD.
A new study published online in Pediatrics May 17 found that the risk of having ADHD increases in children who have higher concentrations of dialkyl phosphate metabolites. The metabolites indicate exposure to organophosphates, pesticides that affect the nervous system, according to the Environmental Protection Agency.
Parents of children with ADHD "often ask me if there are any foods their children should avoid. ... They want to try things besides just giving their child medication," said Dr. Brown, who works in a seven-physician practice in Austin, Texas. "I would add this [study] to the list of things to discuss during consultations about ADHD. ... A lot of parents will be asking about it."
Researchers examined data on 1,139 children age 8 to 15 who were part of the National Health and Nutrition Examination Survey between 2000 and 2004. Of the participants, 10.4% met the diagnostic criteria for ADHD.
Pesticide exposure was measured with a single urine test for six dialkyl phosphate metabolites. Researchers found that 93.8% of the children in the study had at least one detectable metabolite.
One of the most commonly detected metabolites, dimethyl thiophosphate, was found in 64.3% of children studied. Those with higher-than-average levels of this metabolite were two times more likely to have ADHD than those whose levels were undetectable.
"The findings are suggestive of an association of these pesticides and ADHD-like symptoms in children," said study lead author Maryse Bouchard, PhD, a researcher in the Dept. of Environmental and Occupational Health at the University of Montreal. She is also a researcher at the CHU Sainte-Justine Hospital for Children in Montreal.
But she cautioned that additional studies that include multiple urine samples to measure long-term exposure to pesticides are needed to support that exposure to pesticides is linked to ADHD.
The study did not identify the source of the metabolites. But researchers speculated that the children were likely exposed to pesticides and insecticides used on produce or in the environment.
ADHD on the rise
As of 2006, 4.5 million children age 5 to 17 had been diagnosed with ADHD, according to the most recent data available from the Centers for Disease Control and Prevention. New diagnoses rose an average 3% annually between 1997 and 2006.
Seattle pediatrician Catherine Karr, MD, PhD, and colleagues at her practice have noticed an increase in the number of children with ADHD. The question, she said, is whether physicians are better at diagnosing ADHD or the disorder is increasing among children.
"This study helps us better understand what factors might influence a child to develop ADHD. ... And maybe, if we take some of these [factors] away, we won't have so many children diagnosed with this disorder," said Dr. Karr, assistant professor of pediatrics at the University of Washington School of Medicine and adjunct assistant professor of environmental and occupational health sciences at the university's School of Public Health. She also is a member of the American Academy of Pediatrics' Council on Environmental Health.
She said the AAP is developing policy statements that will address the effects of pesticides on children's health and on organic food. The statements are expected to be released in 2011.
"One thing we point out [in the statements] is that currently, medical education is pretty inadequate in all things environmental," Dr. Karr said. "Pediatricians should be better informed on the health implications of pesticides."