The relation of environmental tobacco smoke (ETS) to chronic bronchitis and mortality over two decades

Our aim was to describe how the prevalence of subjects exposed to environmental tobacco smoke (ETS) has changed from 1992 to 2012 in Finland. We also investigated the association between ETS and chronic bronchitis and cause-specific and all-cause mortality.

The study population is composed of 38 494 subjects aged 25-74 years who participated in the National FINRISK Study between 1992 and 2012. Each survey included a standardized questionnaire on exposure to ETS, symptoms of chronic bronchitis, smoking habits and other risk factors, and clinical measurements at the study site. Data on mortality was obtained from the National Causes of Death Register.

In 2012, 5% of the participants were exposed to ETS compared to 25% in 1992. The adjusted odds ratio (OR) for ETS exposure in 2012 compared with that in 1992 was 0.27, p < 0.001. Exposure to ETS was more common in men than in women and among smokers than in non-smokers. Exposure to ETS was in turn associated with chronic bronchitis, OR 1.63 (95% confidence interval 1.49-1.78), - also separately both at work (OR 1.36) and at home (OR 1.69). Subjects with exposure to ETS had significantly increased all-cause (hazard ratio = HR 1.15, 1.05-1.26) and cardiovascular mortality (HR 1.26, 1.07-1.47). However, when stratified by smoking ETS was associated with all-cause mortality only in smokers (HR 1.31, 1.15-1.48).

The proportion of subjects exposed to ETS decreased substantially during the study. Additionally, ETS exposure was associated with chronic bronchitis throughout the study and increased all-cause and cardiovascular mortality.