Second-hand smoke exposure further increases depression risk in smokers

Middle aged and older adults who actively smoke are at increased risk of depressive symptoms, and exposure to second-hand smoke further increases this risk, according to a 20-year prospective cohort study.

Researchers used data from third to ninth waves of the National Institute for Longevity Sciences – Longitudinal Study of Aging database. Baseline data on current cigarette smoking and second-hand smoke exposure were collected. Depressive symptoms were defined as a Center for Epidemiologic Studies Depression Scale score ≥16.

A total of 1,697 participants (mean age 58.7 years, 51.6 percent men) were included in the analysis. Of these, 18.7 percent were current smokers. The mean number of years of education was 12.4, and mean leisure time was 1.68 METs × h/h. The incidence of depressive symptoms ranged from 8 percent (wave four) to 6.5 percent (wave nine), and the mean follow-up was 12.9 years.

The odds of depressive symptoms were similar between current smokers and noncurrent smokers (adjusted odds ratio [aOR], 1.27, 95 percent confidence interval [CI], 0.96−1.68). Subgroup analyses indicated increased odds of depressive symptoms among male current smokers (aOR, 1.40, 95 percent CI, 1.00−1.94) and current smokers aged ≥65 years (aOR, 1.62, 95 percent CI, 1.00−2.63).

Moreover, current smokers exposed to second-hand smoke had greater odds of depressive symptoms compared with unexposed nonsmokers (aOR, 1.50, 95 percent CI, 1.05−2.14) and unexposed current smokers (aOR, 1.39, 95 percent CI, 1.00−1.94).