Background: Although smoking is a well-known risk factor for the onset of airway diseases, the associations between smoking and asthma are inconsistent.
Objective: To examine the relationship of smoking in adulthood with the occurrence of asthma in Japanese individuals.
Methods: A total of 6,674 men and 8,301 women from a population-based cohort in Takayama, Japan, participated in this prospective study. Information on smoking was collected via a baseline questionnaire in 1992. In 2002, development of asthma and the time of physician diagnosis were reported.
Results: During 10-year follow-up, 105 men and 92 women reported the onset of physician-diagnosed asthma. Among men, compared with never smokers, current smokers at baseline had a significantly increased risk of asthma after adjustment for covariates (hazard ratio [HR], 2.79; 95% confidence interval [CI], 1.18-6.55), whereas women with a current or former history of smoking were at an increased but not significant risk of asthma (HR, 1.18; 95% CI, 0.58-2.38). An approximately 2- to 5-fold increased risk of asthma was observed in men who smoked for more than 30 years or more than 21 cigarettes daily, with a nonsignificant linear trend, but there was no dose-response relationship in current-smoking women. Ever-smoking women with husbands who were ever smokers had a higher risk of asthma (HR, 2.02; 95% CI, 0.72-5.65) than never-smoking women with husbands who had never smoked either.
Conclusion: These data suggest that smoking increases the risk of asthma onset in men.