Predictors of Asthma and Wheezing in Adults: Grain Farming, Sex, and Smoking

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Abstract
We investigated predictors for asthma and wheeze in 1,634 men and women in the age group 20 to 65 yr from the town of Humboldt, Saskatchewan. On the basis of questionnaire responses, subjects were classified into mutually exclusive groups as asthmatic (n = 62), wheezing (n = 444), asymptomatic (n = 908), and symptomatic (n = 220) groups. After excluding the symptomatic group, we used polytomous logistic regression models to determine predictors of asthma and wheezing. Significant predictors for asthma were grain farming (odds ratio [OR] = 1.9, 95% confidence interval [Cl]: 1.1-3.5; p = 0.03) and sex (OR = 1.9, Cl: 1.1-3.2; p = 0.03; males compared with females). Significant predictors for wheezing were smoking (former smoker: OR = 1.8, Cl: 1.3-2.5, p < 0.001; current smoker: OR = 5.0, Cl: 3.8-6.7, p < 0.001; in comparison to nonsmoker) and grain farming (OR = 1.7, Cl: 1.3-2.4, p < 0.001). Age, level of education, and physical activity at work were not significant predictors for asthma or wheezing. None of the interaction effects between the predictors was significant. When stratified by sex, grain farming was a significant predictor of asthma in men but not in women. Nevertheless, smoking and grain farming were significant predictors of wheezing in both men and women. Our study raises the possibility that grain farming might be a risk factor for asthma and asthma-like symptoms.