Different effects of smoking on atopic and non‐atopic adult‐onset asthma

BACKGROUND: Both tobacco smoking and atopy increase the risk of adult‐onset asthma. We studied if there are differences in the effects of smoking on the risks of atopic and non‐atopic adult‐onset asthma, and if gender modifies these effects. METHODS: The Finnish Environment and Asthma Study (FEAS) includes 521 incident cases of adult‐onset asthma and 932 population‐based controls, aged 21 to 63 years, recruited from a geographically defined area of Pirkanmaa, South Finland. Asthma was defined based on symptoms and lung function measurements, atopy by IgE antibodies to common aeroallergens and smoking by the study questionnaire. RESULTS: Altogether 212 cases were atopic, and 251 cases were non‐atopic. Regular smoking increased the risk of atopic asthma (adjusted OR 1.24, 95% CI 0.83–1.85), this effect was seen in women (aOR 1.77, 1.06–2.95) but not in men (aOR 0.75, 0.39–1.45). Among regular smokers, the amount smoked was lowest among women with atopic asthma. Recent quitting of smoking was related to increased risk of both atopic (aOR 4.91, 2.26–10.65) and non‐atopic (aOR 4.37, 1.87–10.21) asthma. Having quitted smoking over a year ago was related to increased risk of non‐atopic asthma (aOR 1.57, 1.08–2.28), mainly in men (aOR 2.03, 1.06–3.88). CONCLUSIONS: In women, rather small amounts of regular smoking increase the risk of atopic asthma. However, for non‐atopic asthma, the smoking induced risk continues for longer after quitting, especially in men. In conclusion, the effects of smoking on the risks of atopic and non‐atopic asthma differ, and gender modifies these effects.