Smoking habit and bronchial reactivity in normal subjects. A population-based study.

The relationship between smoking habits and airway responsiveness has been studied in a cross-sectional sample of subjects in a small Lombardy (Italy) town. The subjects were between 15 and 64 yr of age; they were representative of the general population. There were 295 normal nonsmokers, 70 normal smokers, and 50 past smokers. All clinically asymptomatic and functionally normal subjects underwent methacholine challenge. The distribution of responsiveness to methacholine (as expressed by LnPD15FEV1) was found to be significantly different between these normal smokers and nonsmokers. A multinomial logistic regression model showed a statistically significant difference in the response to the challenge on the basis of pack-years. When the number of years of smoking and the daily number of cigarettes were separately considered, the current amount had the significant correlation with LnPD15FEV1. Bronchial reactivity for past smokers was found not to be different from that for normal nonsmokers. We conclude that smoking habits, especially current habits, affect bronchial reactivity even in the absence of airway obstruction.