Associations of self-reported smoking status, serum cotinine level and a composite indicator of smoke exposure with depressive symptoms in middle-aged and elderly U.S. individuals: a cross-sectional study based on the National Health and Nutrition Ex

In the U.S. population aged 45 and older, higher levels of smoke exposure were associated with an increased risk of depression. Increasing public attention and caring for mental health of middle-aged and elderly individuals, especially females, and reducing exposure to smoke will minimize the incidence of depression.