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Examining Epidemiologic Study Flaws and Health Risks

Farmer Spraying PesticideA recent article published by The American Heart Association (AHA) featured the headline, “Pesticide exposure may increase heart disease and stroke risk.” That headline and the study which followed resonated in the press, leading to several articles based on it, said epidemiologist Geoffrey Kabat, Ph.D., in a recent post at the Genetic Literacy Project.

His post, “Viewpoint: Critical flaws plague new study linking ‘heavy’ pesticide exposure to cardiovascular disease”, describes issues with the methodology used and study limitations that he believes undermine its conclusions. Dr. Kabat, formerly of Einstein, also explains why problems in epidemiologic studies such as this one result in the public and the mainstream media being misled about health risks.

The following is an excerpt from Dr. Kabat’s post.

“The study in question, conducted by researchers in Hawaii, made use of a long-standing cohort of 7,557 middle-aged Japanese-American men to examine the association between pesticide exposure and cardiovascular disease. The cohort had been enrolled as part of the Honolulu Heart Program in 1965-1968 and was followed for up to 34 years to 1999.

The authors conducted two analyses of the association between pesticide exposure and risk of cardiovascular disease, after 10 years and 34 years of follow-up. In the abstract to the paper, they reported that there was a positive association between a high level of pesticide exposure and risk of cardiovascular disease (CVD) in the first 10 years of follow-up.
They concluded:

“These findings suggest that occupational exposure to pesticides may play a role in the development of cardiovascular diseases. The results are novel, as the association between occupational exposure to pesticides and cardiovascular disease incidence has not been examined previously in this unique cohort.”

Like all reports of epidemiological findings, this paper needs to be examined carefully to see what information the researchers had, how exposure was defined, how the data were analyzed, and how convincing the results are. Cardiovascular disease is the leading cause of death in the US, and any new environmental risk factor for the disease, if prevalent in the general population, would be of great importance for public health.

But, as soon as I got into the actual details of the study, I realized that the reported association between pesticide exposure and CVD can only be sustained by failing to subject the data to critical analysis. In fact, there are many glaring deficiencies in the data, in the analysis, and in the conclusions.”

To read more of this article, please visit the Genetic Literacy Project.

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