Influence of farm environment on asthma during the life-course: a population-based birth cohort study in Northern Finland

Introduction: It is increasingly recognized that exposure to farming environment protects against asthma in childhood. However, the evidence of childhood farm exposure on asthma during the life-course is scarce and inconsistent. Aims and objectives: To investigate the influence of farming environment on asthma in three time points from birth to 46 years using data from the Northern Finland Birth Cohort 1966 (n = 10 926). Exposure to farming environment in childhood was hypothesized to protect from asthma from birth to middle age. Methods: The prevalence of asthma was measured by a postal questionnaire at age 14, 31 and 46 years. Exposure to farming environment was measured by a postal questionnaire at birth and at age 31 and 46 years. Odds ratios (OR) and their 95% confidence intervals (95% CI) for the prevalence of asthma were obtained from multinomial logistic regression, stratified by gender. The analyses were adjusted for smoking, socio-economic position, birthweight, BMI, family size, living place, pets, sports, diet and occupational farming. Results: Being born in a farmer family predicted lower prevalence of asthma in females at age 14 (OR 0.11, 95% CI 0.01, 0.94), 31 (OR 0.62, 95% CI 0.39, 0.97) and 46 (OR 0.60, 95% CI 0.38, 0.97) years and in males at age 31 years (OR 0.59, 95% CI 0.35, 0.99). Working as a farmer was not associated with asthma at age 31 and 46 years. Conclusions: Exposure to farming environment in childhood demonstrates a protective effect on asthma from birth to 46 years, indicating that ‘immune deviation’ may take place throughout life. The effect is more consistent in females compared to males.