Is there a causal relation between obesity and asthma? Evidence from Chile.

OBJECTIVE: An association between obesity and asthma symptoms has been reported in the literature, but such a relationship is inconsistent if atopic status or bronchial hyper responsiveness (BHR) is considered. The objective was to assess the association between obesity and asthma symptoms or BHR in adults.
METHODS: A study was carried out in 1232 people born between 1974 and 1978 in Chile. The participants completed the European Community Health Survey questionnaire, were skin tested and subject to a BHR challenge to methacholine. MEASUREMENTS: Weight, height and waist circumference were measured and body mass index (BMI) was calculated.
RESULTS: There was a positive association between wheeze and breathlessness following exercise and BMI (both with an OR 1.03, 95% CI 1.00-1.06), the associations with wheeze tended to disappear in women who did react at least to one allergen, and persisted in those who did not react to any allergens. BMI was negatively associated with BHR (OR 0.93, 95% CI 0.89-0.97). Waist circumference was not associated with asthma symptoms and it was negatively associated with BHR.
CONCLUSION: Although there was an association between BMI and asthma symptoms, there were weaknesses in the evidence because waist circumference, a more direct measure of obesity than BMI, was not associated with asthma symptoms, and BMI and waist circumference were negatively associated with BHR.