Smoking and asthma in adults.
Studies on the effect of smoking on adulthood asthma have provided contradictory results. The current authors conducted a population-based incident case-control study to assess the effects of current and past smoking on the development of asthma in adults. During a 2.5 yr study period, all new asthma cases clinically diagnosed (n=521) and randomly selected controls (n=932) from a geographically defined district in southern Finland were recruited. The risk of developing asthma was significantly higher among current smokers with an adjusted odds ratio (OR) of 1.33 (95% confidence interval 1.00-1.77) and among ex-smokers with an adjusted OR 1.49 (1.12-1.97) compared with never-smokers. Among current smokers, the risk increased up to 14 cigarettes x day(-1), and a similar trend was observed in relation to cumulative smoking. In conclusion, the current results support the hypothesis that smoking causes asthma in adulthood.