Long-term smoking behavior patterns predicting self-reported chronic bronchitis.

We examined the effects of long-term smoking patterns on self-reported symptoms of chronic bronchitis within the Finnish adult twin cohort including 21, 609 individuals responding to questionnaires in 1975 and 1981, of which 11,015 respondents participated also in 1990. We also explored the association between smoking and bronchitis among discordant twin pairs. Among those without chronic bronchitis at baseline we examined incidence of chronic bronchitis in 1981 both by 1975 smoking status, but also based on subgroups formed according to change in smoking behaviors between 1975 and 1981. We conducted similar analyses in the longitudinal data including three consecutive measurements of smoking status. Logistic regressions demonstrated that among current smokers, the risk of chronic bronchitis increased about 1.5-fold by each amount category of daily cigarettes. When analyzing change of smoking status between 1975 and 1981, daily moderate and heavy smokers, smoking increasers and decreasers, as well as re-current smokers demonstrated elevated risks. In the analysis among discordant twin pairs the smoking co-twins had a 14-fold likelihood for chronic bronchitis compared to their never-smoking co-twins. Panel analyses showed that, not only moderate and heavy, but also former and light smokers, had significant risks for chronic bronchitis. Those with late smoking initiation, leisure time physical activity or over 10 years of smoking cessation were less likely to have chronic bronchitis. We conclude that in long term evaluation no safe level of smoking exists. Abstinence from tobacco seems to be the public health message justified by these results in prevention of chronic bronchitis.