Is there a relationship between smoking and asthma in adults?

A case-control study was carried out to investigate the possibility of a relationship between smoking and asthma in adults. The study group of 141 asthmatic adults and 423 age- and sex-matched non-asthmatic controls were selected from 4341 men and women aged 18 years and over, who were registered with a family practice. Both groups were interviewed by telephone about past and present smoking habits. Current smokers constituted 22% of the asthmatic group and 15% of the controls (not significantly different). The prevalence of those who had given up smoking (quitters) was significantly higher in asthmatics than in controls (8.5% versus 3.6%). Asthma began at younger ages in smokers than in quitters and non-smokers. In smokers, the duration of smoking was associated with the duration of asthma. No other significant differences in or associations between smoking habits and asthma were found. No major relationship between smoking and asthma was demonstrated.