CIGARETTE-SMOKING AND INCIDENCE OF CHRONIC-BRONCHITIS AND ASTHMA IN WOMEN

Study objective: To examine the relation of smoking habits and develop ment of asthma in a large cohort of US women. Design: Prospective coho rt study. Participants: Among 74,072 women, 34 to 68 years of age, who were free of major diseases, we documented 671 incident asthma cases and 798 incident cases of chronic bronchitis during 10 years of follow -up. Methods: Age-adjusted relative risk estimates for smoking categor ies were calculated separately for chronic bronchitis and asthma. Resu lts: Risk of chronic bronchitis was significantly higher in current sm okers than in never smokers (relative risk [RR] =2.85; 95% confidence interval [CI] =2.45 to 3.32) and increased with the number of cigarett es smoked per day (p for trend <0.0001), Approximately 5 years after q uitting, chronic bronchitis risk in past smokers approached that in ne ver smokers, In contrast, current smokers were at significantly lower risk for asthma than women who never smoked (RR=0.57; 95% CI=0.46 to 0 .71) and women who quit (RR=0.50; 95% CI=0.40 to 0.62), possible becau se individuals with sensitive airways are less likely to become regula r smokers, and smokers who develop respiratory symptoms of any etiolog y tend to quit. Asthma risk in past smokers initially increased compar ed with that in never smokers, possibly because of quitting prior to d iagnosis in response to symptoms of any etiology, but decreased with t ime since quitting (p for trend=0.007); within approximately 5 years, the risk did not differ between past and never smokers. Conclusion: Th ese data suggest that smoking in adults may not be an independent caus e of asthma but could exacerbate or be perceived as exacerbating asthm a symptoms in susceptible individuals.