According to a new study in Pediatrics, there might be a relationship between exposure to certain pesticides and ADHD. The study found that children who had a higher level of organophosphate pesticide by-products in their urine were significantly more likely to have a diagnosis of ADHD.
Flickr photo by andypowe11
The study is freely available, so if you are interested I suggest you read it from yourself.
The first question that came to mind when I read this study is exactly what is an organophosphate pesticide. An organophosphate pesticide is a type of insecticide that is widely used in agriculture, the home, gardens, an veterinary practice. These pesticides work by disrupting the normal function of the nervous system and affect people as well as insects (some organophosphates were used in World War II as nerve agents). However, these chemicals do not persist for long in the environment so are thought to be safer than the chemicals that they replaced (such as DDT).
In this study there were a total of 1,139 children between the ages of 8 and 15. Of these children, 119 met strict criteria for ADHD while an additional 30 children did not currently met the criteria but were on medications for ADHD. Since ADHD, like autism, is behavioral based diagnosis you need to consider those children whose behaviors are currently being controlled by medication and don't currently appear to have ADHD. The prevalence of ADHD in these children was about 12.1% percent which is slightly higher than the national average but isn't too far out of line.
Think about that number for a minute - one out of every ten children has a form of ADHD. You may be one of those people who think that this diagnosis is overused or that this is just an excuse for misbehaving children, and I am sure that there is some of that going on. But ADHD, like autism, is a large problem in this country and awareness and/or other social factors cannot account for the scope and magnitude of the growth.
All of the children in the study had a urine sample collected and these samples were analyzed to try to determine exposure to a organophosphate pesticides. Since these chemicals are broken down by the body, the researchers could not directly measure the exposure level in the urine. Instead the researchers looked at the levels of 6 different metabolites (by-products). The majority of children (94%) had a detectable level of at least one of the metabolites, meaning that the majority had at least some exposure to these pesticides.
The researchers found that children with a higher levels of these metabolites had a greatly increased chance of having ADHD, even after taking into account gender, race, income level, body mass index (BMI), blood lead level, maternal age at birth, and maternal smoking during pregnancy. The exact risks varied from depending on the metabolite in question and varied from a low of 20% greater chance (odds ratio 1.21) all the way to a 100% greater chance (odds ratio 2.09).
The interesting thing to me is that these children had what would be considered an "average" level of exposure to these pesticides. The majority of the exposure in these children is thought to be from dietary sources and residential usage. Or in other words, most children in the US would have a similar level of exposure.
On the flip side, there are some potential problems with the study.
The result is based on a single urine sample and measures exposure at a specific point in time. Since these chemicals are thought to be cleared from the body in a matter of days, this sample would only measure short term exposure and does not mean that the at-risk children had a continuing higher exposure.
The other problem is that this study does not establish what the nature of the relationship is - it does not say that higher exposure to pesticides causes ADHD. It is possible that children with ADHD have behaviors that give them a higher exposure, perhaps by favoring a certain type of food. Or perhaps the relationship is just a fluke of the data set.
Regardless, this is definitely something that needs to be researched further.
1: Bouchard MF, Bellinger DC, Wright RO, Weisskopf MG.
Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides. Pediatrics. 2010 May 17. [Epub ahead of print] PubMed PMID: 20478945.