Abstract

Background: To our knowledge only one previous study has addressed effects of smoking on lung function in adult asthmatics, who may form a susceptible group. We assessed the relations between current, former and life-time cumulative smoking and lung function among adults with new asthma.

Methods: In a population-based study 521 (response rate 86%) working-aged adults with clinically defined incident asthma answered a questionnaire on personal smoking and other factors potentially influencing lung function, and performed spirometry.

Results: Among asthmatics FEV1 level was reduced on average 220 ml related to current smoking (effect estimate -0.22, 95% CI -0.38 to -0.06) and 230 ml in relation to former smoking quit less than a year ago (-0.23, 95% CI -0.49 to 0.03), but FEV1 was not related to occasional smoking or former smoking quit over a year ago. The relation with smoking was stronger in men and an exposure-response pattern related to both daily smoking rate and life-time cumulative smoking was seen both among men and women.

Conclusions:This study provides new evidence that among working-aged adults with new asthma, regular smoking and former smoking are related to reduced FEV1 level. Men seemed to be more susceptible to this effect. The results indicate that those with asthma should not start smoking or should be encouraged to quit at their earliest convenience.