Common pesticied linked to Parkinson's

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Fact-Checking a Claim About a Weed Killer

LONDON — Syngenta, the Swiss pesticide giant, claims on its website that data from an influential 2011 study shows that farmers who use the weed killer paraquat are less likely to develop Parkinson’s disease than the general population.

However, Syngenta’s claim is at odds with the actual findings of the study, according to two of its authors.

The 2011 study, carried out by the National Institutes of Health and researchers from other institutions around the world, found that people who used paraquat or another pesticide, called rotenone, were roughly two and a half times more likely to develop Parkinson’s.

The work is known as the Farming and Movement Evaluation, or FAME, study. It drew on a sweeping United States government project called the Agricultural Heath Study, which tracked more than 80,000 farmers and their spouses, as well as other people who applied pesticides, in Iowa and North Carolina.

The FAME researchers identified 115 people from the Agricultural Health Study who developed Parkinson’s, and studied 110 of them who provided information on the pesticides they used.

The study was influential even among some people who had been skeptics of a connection between the chemicals and the disease. Gary W. Miller, a professor of environmental health at Emory University, referred to a link between Parkinson’s and paraquat as a “red herring” in a 2007 publication. But while Dr. Miller said in a recent email exchange that he had concerns about some previous research making the connection, “the FAME data are strong and should be considered.” He said the study “appears to show a connection between paraquat exposure and Parkinson’s disease.”
Because of the prominence of the FAME study, Syngenta addresses it on one of its websites, paraquat.com. Syngenta claims that the study shows that only 115 people had Parkinson’s out of the more than 80,000 people in the broader Agricultural Health Study. Therefore, “the incidence of Parkinson’s disease” in the study “appears to be lower than in the general U.S. population,” Syngenta says.

But the FAME study was not a comprehensive assessment of the incidence of Parkinson’s disease among those in the wider Agricultural Health Study. Rather, researchers picked out a group of people who did have Parkinson’s and specifically studied them against a control group.

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