Influence of Childhood Exposure to a Farming Environment on Age at Asthma Diagnosis in a Population-Based Study.

Purpose Asthma is a heterogeneous disease, and factors associated with different asthma phenotypes are poorly understood. Given the higher prevalence of farming exposure and late diagnosis of asthma in more rural Western Finland as compared with the capital of Helsinki, we investigated the relationship between childhood farming environment and age at asthma diagnosis. Methods A cross-sectional population-based study was carried out with subjects aged 20-69 years in Western Finland. The response rate was 52.5%. We included 3864 participants, 416 of whom had physician-diagnosed asthma at a known age and with data on the childhood environment. The main finding was confirmed in a similar sample from Helsinki. Participants were classified as follows with respect to asthma diagnosis: early diagnosis (0-11 years), intermediate diagnosis (12-39 years), and late diagnosis (40-69 years). Results The prevalence of asthma was similar both without and with childhood exposure to a farming environment (11.7% vs 11.3%). Allergic rhinitis, family history of asthma, ex-smoker, occupational exposure, and BMI ≥ 30 kg/m2 were associated with a higher likelihood of asthma. Childhood exposure to a farming environment did not increase the odds of having asthma (aOR, 1.10; 95% CI, 0.87-1.40). It did increase the odds of late diagnosis (aOR, 2.30; 95% CI, 1.12-4.69), but the odds were lower for early (aOR, 0.49; 95% CI, 0.30-0.80) and intermediate diagnosis of asthma (aOR, 0.75; 95% CI, 0.47-1.18). Conclusion Odds were lower for early diagnosis of asthma and higher for late diagnosis of asthma in a childhood farming environment. This suggests a new hypothesis concerning the etiology of asthma when it is diagnosed late.