Smoking and mental health: Cross-sectional and cohort studies in an occupational setting in Japan

Background. The relationship between smoking and mental health remains unclear. Methods. We carried out a cross-sectional study and a cohort study on the possible association of smoking and mental health in 782 workers. Using a questionnaire including the 30-item General Health Questionnaire (GHQ-30) and items related to the smoking state, the association between smoking and mental health was evaluated separately in males and females. The subjects were classified into smokers and nonsmokers, and changes in the GHQ score during a 2-year follow-up period were evaluated. To control potential confounding factors, multiple regression analyses were performed. Results. The cross-sectional study showed no difference in the GHQ score between smokers and nonsmokers among males but a significantly higher GHQ score for smokers than nonsmokers among females. This difference among females was confirmed to be significant by multiple regression analysis. The 2-year cohort study showed a decrease in the GHQ score in each group and no reduction in the difference in the GHQ score between smokers and nonsmokers among females. Conclusions. No difference was observed in mental health between smokers and nonsmokers in males. However, in females, smokers showed poorer mental health than nonsmokers, and this difference remained unchanged even after 2 years.