Exposure to pesticides a risk factor for Parkinson s? Not so fast!

ASCH Staff @ American Council on Science and Health

A new study published in the journal Neurology tries to suggest that there may be an association between exposure to pesticides and solvents and Parkinson s disease. Even the study authors are blatantly aware of the shortcomings of their study when they say, the evidence is limited, or at least inconclusive, because of lack of definitive agreement between cohort and case-control studies. Yet that didn t stop them from publishing it. This meta-analysis was based on 89 prospective and case-control studies considering a range of chemicals pesticides, herbicides, insecticides, fungicides, rodenticides, solvents, organophosphates, paraquat, and DDT, among others and their relation to Parkinson s. After analysis, researchers concluded that risk of developing Parkinson s was increased by 33 percent to 80 percent due to exposure to these chemicals.

The analysis was a first-rate mess. Conclusions from the included studies were not in agreement the majority of the time, and even higher quality studies showed statistically significant associations for solvents, paraquat, and well-water drinking but they also found reductions in Parkinson s for exposure to insecticides, farming and well-water drinking.

How can something well-water drinking both increase risk of Parkinson s and also decrease risk? The answer: garbage science. As if to prove this point, the case-control studies differed in terms of study quality and size and in the prospective studies, estimates of exposure were not determined in the same way. And secondary causes of Parkinson s were completely ignored by the authors.

ACSH s Dr. Gilbert Ross says, This is a prime example of a bad study; it could be used as an illustration in a college text on how not to do epidemiology. First of all, there was so much variation between studies, a point even the authors are aware of, that definitive conclusions cannot be made. And results were clearly contradictory as pointed out in the well-water example previously. The one good point made by study authors was that no association was found between DDT and Parkinson s.

ACSH s Dr. Josh Bloom points out that the entire premise is biologically implausible. He says, There is no way that you can lump these substances together and draw any type of valid conclusion. They are all chemically different, work by different mechanisms, and each one is processed in the body in a different way. This is like saying since a cannon ball is round and kills people, all other round objects are dangerous. He continues, According to this logic, perhaps the Department of Homeland Security ought to think about banning Nerf Balls.