Body mass index and physical activity in relation to asthma and atopic diseases in young adults.

Background: Obesity has been shown to increase the risk of asthma and wheezing. Conditioning exercise might decrease the asthma risk, and that could partly explain the association. The relation between obesity and allergic diseases is quite conflicting.

Methods: The association between body mass index (BMI) and physician-diagnosed asthma, allergic rhinitis or conjunctivitis, atopic dermatitis, and self-reported wheezing was investigated in a questionnaire study among 10,667 Finnish first-year university students aged 18-25 years. Logistic regression was used to evaluate possible confounding by parental education, passive smoking at age 0-2, childhood residential environment, current and past smoking and leisure time physical activity index.

Results: In men, there was a greater risk of asthma, but not wheezing with increasing BMI. Compared to those with BMI below 20, OR for male asthma was 1.98 (95% CI 1.11-3.52) in BMI category 20.0-22.4, 1.90 (95% CI 1.05-3.41) in BMI 22.5-24.9, and 3.5 (95% CI 1.63-7.64) in BMI > or = 27.5. Among women, the risks of asthma and wheezing were about two-fold among the overweight-obese subjects. Moderate leisure time physical activity was associated with lower risk of asthma in men (OR 0.62, 95% CI 0.62 (0.42-0.92), but not among women. The risk of allergic rhinoconjunctivitis and atopic dermatitis increased quite linearly with BMI among women but not men.

Conclusions: Low leisure time physical activity seems not to explain the greater risk of asthma among obese men and women. The quite linear association between BMI and both allergic rhinoconjunctivitis and wheezing among women suggests the independent effect of body fat on atopic diseases.