Pesticide Exposure Linked to Asthma in Farm Workers

Pesticides could be putting some farm workers at a higher risk of developing asthma.  Women who work on farms and who use pesticides are more likely than nonpesticide users to develop allergic asthma as adults, a U.S. study shows.  <"">Asthma is a chronic inflammation of the bronchial tubes, or airways, causing airway constriction and resulting in breathing difficulties. The bronchial narrowing is usually either totally or at least partially reversible with treatments. Chronically inflamed bronchial tubes may become overly sensitive to allergens (specific triggers) or irritants (nonspecific triggers).  The airways may become twitchy, remaining in a state of heightened sensitivity called “Bronchial Hyper-Reactivity” (BHR).   It is likely that there is a spectrum of bronchial hyper-reactivity in all individuals; however, it is clear that asthmatics have a greater degree of bronchial hyper-reactivity than nonasthmatic and nonallergic people.  In sensitive individuals, bronchial tubes are more likely to swell and constrict when exposed to triggers such as allergens, tobacco smoke, or exercise.  Among asthmatics, some may have mild BHR and no symptoms while others may have severe BHR and chronic symptoms.

This effect is particularly strong for the 60% of farm women who grew up on a farm. People who grow up on farms have a reduced risk of allergies. Pesticide users have less of this protection, find Jane A. Hoppin, ScD, of the National Institute of Environmental Health Sciences, and colleagues.  “Growing up on a farm is such a huge protective effect it’s pretty hard to overwhelm it,” Hoppin said in a news release. “There is a difference in asthma prevalence between women who did and did not use pesticides, but whether it is causal or not remains to be seen.”

Hoppin’s team collected self-reported data from 25,814 farm women from Iowa and North Carolina. This data included detailed information on pesticide use and whether, as adults, they had doctor-diagnosed allergic or nonallergic asthma.  Farm women who grew up on farms were about half as likely to have allergic asthma—and about 20% less likely to have nonallergic asthma—as were women who were not farm children. Yet, pesticide use was most strongly linked to allergic asthma in farm-raised women.  “It is likely that the association with pesticides is masked in the general population due to a higher baseline rate of asthma,” Hoppin suggests.  Use of any pesticide on the farm upped a woman’s risk of allergic asthma by 46%, but did not increase risk of nonallergic asthma.  Even so, the risk was not large.  Only 181 of 14,767 pesticide users reported allergic asthma.  Ten of 31 analyzed pesticides were linked to allergic asthma, including two herbicides (2,4-D and glyphosate), seven insecticides (carbaryl, coumaphos,
DDT, malathion, parathion, permethrin on animals, and phorate), and one fungicide (metalaxyl).  “Pesticides, particularly organophosphate insecticides, may increase asthma risk,” Hoppin and colleagues conclude.

Just because there is a link between pesticides and allergic asthma doesn’t necessarily mean pesticides cause asthma.  Hoppin says that in 2008, her team is hoping to start a new study to better evaluate this link.  Their current report appears in the January 1st issue of the American Journal of Respiratory and Critical Care.

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