Aims To measure reduction in exposure to smoke in two population-based studies of self-reported smoking reduction not using nicotine replacement.
Design Cross-sectional analyses of biomarkers and smoking.
Setting Data from two time-points in the Copenhagen City Heart Study (CCHS), 1981/83 and 1991/94, and the Copenhagen Male Study (CMS) in 1976 and 1985/86, respectively.
Participants There were 3026 adults who were smokers at both time-points in the CCHS and 1319 men smoking at both time-points in the CMS.
Measurements Smoking status and tobacco consumption were assessed by self-completion questionnaire. Measurements of biomarkers of smoke intake were taken at the second time-point in the two studies: expired-air carbon monoxide (CO) in the CCHS and serum cotinine in the CMS. Biomarker levels in medium (15–29 g tobacco/day) and heavy (> 30 g/day) smokers at the first time-point who later reported a reduction in cigarettes per day of 50% or more without quitting were compared with continuing medium, heavy and light smokers (1–14 g/day) using linear regression. Sex (CCHS only), age, self-reported inhalation of smoke, duration of smoking, type of tobacco and amount smoked were included as covariates in multivariate models.
Findings Heavy smokers who reduced did not show lower levels of biomarkers at follow-up. Medium smokers who reduced showed a reduction in cotinine but not CO. The reduction in cotinine was not commensurate with the reported reduction in consumption.
Conclusions Long-term reductions in self-reported tobacco smoking are probably associated with, at best, modest reductions in smoke exposure.