Study Finds Pesticide Exposure Increases Risk of Asthma

(Beyond Pesticides, January 4, 2008)

A study appearing in the January 2, 2008 issue of the American Journal of Respiratory and Critical Care Medicine has found a correlation between women’s exposure to farm pesticides and allergic asthma. The study’s lead author, Jane Hoppin, Sc.D., of the National Institute of Environmental Health Sciences, cited the lack of information on the risks incurred when women apply pesticides, saying, “Farm women are an understudied occupational group.”

The study evaluated data on 25,814 farm women who are participating in the Agricultural Health Study in Iowa and North Carolina. “This is the largest study of farmers and their families in the world, so it gives us an opportunity to look at diseases that haven’t been well characterized,” said Dr. Hoppin. The women self-reported their doctor-diagnosed asthma, and the team separated them into subgroups of allergic and non-allergic asthmatics. They also found that more than half of the responders had used or been exposed to pesticides, while 61 percent grew up on a farm.

The resulting data found that use of pesticides increased risk of allergic asthma by almost 50 percent, but not of non-allergic. Where a woman grew up also affected her likelihood to develop allergic asthma. Women who were raised on farms and did not handle pesticides had the lowest risk of asthma. Women who who grew up on a farm and did work with pesticides were more likely to be asthmatic. Women who did not grow up on farms, however, were most likely to develop asthma, due to a little-studied protective affect of growing up in an agricultural setting, which provides an overall reduction in risk.

“Growing up on a farm is such a huge protective effect it’s pretty hard to overwhelm it,” said Dr. Hoppin. “[But] about 40 percent of women who work on farms don’t report spending their childhoods there. It is likely that the association with pesticides is masked in the general population due to a higher baseline rate of asthma.”

The study also divided out the different pesticides used by respondents and their correlation to the asthma rate. Malathion, for example, was associated with a 60 percent increase in incidence of allergic asthma. According to the report, “A total of 7 of 16 insecticides, 2 of 11 herbicides, and 1 of 4 fungicides were significantly associated with atopic [allergic] asthma; only permethrin use on crops was associated with nonatopic [non-allergic] asthma,” in spite of non-allergic asthma’s higher occurrence in adults.

A follow-up study has been planned to better evaluate the link between pesticides and asthma. “We want to characterize the clinical aspects of the disease, as well as lifetime exposures to agents that may either protect against asthma or increase risk,” said Dr. Hoppin. “We hope to start the study in 2008.”

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