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According to the Centers for Disease Control and Prevention (CDC), between 3 and 7 percent of the school-age child population suffer from attention deficit hyperactivity disorder (ADHD) in the United States. The rates of ADHD vary by gender: 9.5 percent of boys have the disorder, while 5.9 percent of girls have ADHD, notes the CDC. But what causes ADHD? As the MayoClinic.com points out, researchers have noted several factors that may contribute to the onset of the disorder. For example, ADHD patients may have differences in their brain structure that result in the symptoms. But exposure to certain chemicals, such as pesticides, may also play a role in who develops ADHD.
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Types of Pesticides Linked to ADHD
One such pesticide linked to ADHD is organophosphates. Over 40 types of organophosphates are registered in the United States according to the National Pesticide Information Center. Settings for organophosphate use include farms, homes, and veterinary offices. Organophosphates can enter a person's system by penetrating their skin or if they injest or inhale the pesticide. Once the pesticide enters the body, organophosphate causes excess amounts of the neurotransmitter acetylcholine (ACh) by interfering with the enzyme acetylcholinesterase (AChe). Some of the signs of organophosphate poisoning include dizziness, headache, weakness, and muscle twitching.
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Research on Pesticides Linked to ADHD
Several studies have investigated pesticides linked to ADHD. In one study published in Pediatrics, the authors looked at the urinary levels of organophosphate metabolites in 1139 children between the ages of 8 and 15. The data for the study came from the National Health and Nutrition Examination Survey (NHANES) from 2000-2004 when the National Center for Health Statistics of the Centers for Disease Control and Prevention assessed for ADHD. To diagnose ADHD, the Diagnostic Interview Schedule for Children (DISC-IV) was used. The authors reported that they found “an association between urinary DMAP metabolite concentrations, which are indicators of exposure to dimethyl-containing organophosphate pesticides, and increased odds of ADHD for children 8 to 15 years of age.” The authors noted a limitation in their study: they measured the metabolites in one spot urine sample, rather than multiple measurements over time.
Another study on pesticides linked to ADHD was conducted at the UC Berkeley School of Public Health. The authors examined the effects of maternal exposure to organophosphates during the pregnancy on attention problems. The study included over 300 children who were part of the Center for Health Assessment of Mothers and Children of Salinas. The authors tested for metabolites two times during the pregnancy and multiple times in the children after they were born. According to the press release from UC Berkeley, the authors found a link between prenatal exposure to organophosphates and attentional problems at the age of five.
While these studies do show some link between pesticides and ADHD, some are skeptical about a causal relationship. In her Psychology Today blog, Dr. Stephanie Sarkis points out that in the Pediatrics study, the diets of the children were not part of the study. She brings up the point that ADHD patients may have more trouble than non-ADHD patients breaking down organophosphates. In the UC Berkeley study, the authors note that in 2-year-old participants who have lower levels of the enzyme paraoxonase 1 (PON1), they had more neurodevelopmental delays. PON1 is involved in the breakdown of the toxic organophosphate metabolites. Further studies into pesticides linked to ADHD may provide more insight into the connection.
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CDC: ADHD, Data and Statistics
MayoClinic.com: Attention-deficit/hyperactivity disorder (ADHD): Causes
National Pesticide Information Center: Organophosphate Insecticides
Bouchard, M.F., Bellinger, D.C., Wright, R.O., and Weisskopf, M.G. (2010). Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides. Pediatrics 125(6) pp. 1270-1277
University of California, Berkeley: Prenatal pesticide exposure linked to attention problems in preschool-aged children
Psychology Today: Pesticides Cause ADHD? What??