Pesticides may increase the risk of allergic asthma for women who work on farms, especially those not exposed early in life.

by Crystal Phend, Staff Writer, MedPage Today


Research Triangle Park, N.C., Dec. 28
 — Pesticides may increase the risk of allergic asthma for women who work on farms, especially those not exposed early in life.

Handling pesticides was associated with an increased risk of atopic asthma of 46% and lifetime use of three or more agricultural chemicals was associated with an increased risk of 63% compared with the risk for farm women who never used pesticides, according to an observational study in the Jan. 1, 2008 issue of the American Journal of Respiratory and Critical Care Medicine.

However, growing up on a farm tended to be protective even for women who applied or mixed pesticides (odds ratio: 0.73, 95% confidence interval: 0.53 to 1.01), found Jane A. Hoppin, Sc.D., of the National Institute of Environmental Health Sciences here, and colleagues.

The study provided a unique look at the respiratory effects of pesticides, which are likely obscured in the general population because of a higher baseline rate of asthma, Dr. Hoppin said.

Although studies have linked pesticides, particularly organophosphate insecticides, to wheeze among farmers, little research has focused on respiratory hazards among female agricultural workers.

Dr. Hoppin’s group analyzed outcomes for 25,814 women in the prospective Agricultural Health Study of a cohort of people who applied pesticides and their spouses in Iowa and North Carolina.

The women reported physician-diagnosed asthma, exposure to 50 specific agricultural chemicals, and other factors on questionnaires or in telephone interviews.

Among them, 702 women reported adult-onset asthma (2.7%). Most cases were nonatopic (60%).

The 61% of women who reported spending at least half of their childhood on a farm were less likely to have atopic asthma than those who did not (OR: 0.55, 95% confidence interval: 0.43 to 0.70).

Although those who grew up on a farm also tended to have less nonallergic asthma (OR: 0.83, 95% CI: 0.68 to 1.02), the associations found for pesticides and other exposures in the study were almost exclusively with atopic asthma.

The majority of women (57%) reported applying pesticides at some point in their life.

Any pesticide use — handling, mixing, or applying — was associated with an elevated likelihood of atopic asthma (OR: 1.46, 95% CI: 1.14 to 1.87) but not nonatopic (OR: 1.00, 95% CI: 0.82 to 1.22).

Women who grew up on a farm but did not apply pesticides were at lowest risk overall of atopic asthma (OR: 0.41 versus no pesticide application or early farm exposure, 95% CI: 0.27 to 0.62).

Among the pesticides, seven of 16 insecticides, two of 11 herbicides, and one of four fungicides were linked to atopic asthma.

The strongest associations were for organophosphate insecticides, as has been found in previous studies. The odds of atopic asthma for women who reported handling these chemicals were 2.88 for parathion (95% CI: 1.34 to 6.20), 2.19 for coumaphos (95% CI: 1.02 to 4.69), and 2.04 for phorate (95% CI: 1.07 to 3.88).

However, the two insecticides most commonly used by the cohort were also significantly associated with allergic asthma, with odds ratios of 1.60 for malathion (95% CI: 1.22 to 2.10) and 1.41 for carbaryl (95% CI: 1.10 to 1.80).

Only one pesticide — the commonly used crop insecticide permethrin — increased risk of nonatopic asthma as well (OR: 2.19, 95% CI: 1.33 to 3.61).

Increasing duration and frequency of use did not appear to raise asthma risk in a dose-dependent manner.

The reason for the lack of associations with nonatopic asthma “could be that factors affecting risk for atopic asthma reflect primarily risk of atopy, and not asthma per se,” Dr. Hoppin and colleagues wrote.

However, a sensitivity analysis suggested atopy alone could not fully explain the difference in associations between atopic and nonatopic asthma, they said, because risk was consistently greater among those with atopic asthma than those with atopy alone.

The researchers cautioned that their study could not establish a causal or temporal association between asthma and pesticide exposure. It also suffered the problems of all studies that rely on self-reporting.

The researchers reported no conflicts of interest. 


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Reviewed by Zalman S. Agus, MD; Emeritus Professor, University of Pennsylvania School of Medicine.

Resources

American Journal of Respiratory and Critical Care Medicine 

Source Reference

Hoppin JA, et al “Pesticides and atopic and nonatopic asthma among farm women in the agricultural health study” Am J Respir Crit Care Med 2008; 177: 11-18.