Relationship between Smoking and Major Depression in a Japanese Workplace

Smoking and depression are among the most common and serious health problems in the world. More than 25% of smokers are reported to show some symptoms of depression 1) , and 70% of men and 80% of women with a history of major depression are estimated to have a smoking habit 2) . The relationship between smoking and depression has shown an association between smoking and depression, but the causal relationship is unknown. Thus in the present study we have two research tasks: one is to conduct a cross-sectional study with the database for the first year in order to clarify the prevalence of major depression in smoking status. In addition to smoking status, the Brinkman index 3) was used as a nicotine parameter to examine the causal relationship of smoking to depression. The second task is to conduct a cohort study, examining the causal relationship of major depression in the first year to smoking in the following year by assessing the risk of smoking progression or the potential for smoking cessation associated with prior depression. To investigate the causal relationship between smoking and depression in both directions, the risk for the onset or improvement of depression associated with the prior smoking status was also examined in the present study.