Dose-response relations between second-hand smoke exposure and depressive symptoms among middle-aged women

A growing body of evidence indicates a strong association between smoking and depression. However, little is known about the possible effects of second-hand smoke (SHS) exposure on depression. This study aimed to examine the potential dose-response relation between SHS exposure and depressive symptoms among non-smoking middle-aged women. A cross-sectional survey was conducted using a stratified three-stage sampling method. Depressive symptoms were measured by the Center for Epidemiologic Studies Depression Scale with a cut-off point of 16. Self-reported SHS exposure was defined as non-smokers׳ inhalation of the smoke exhaled from smokers on at least one day a week. The multivariable logistic regression analysis was completed with adjustment for potential confounders. Among 1280 middle-aged women, 19.4% were classified as having depressive symptoms. There was a 104% increased odds of depressive symptoms corresponding to SHS exposure in general (OR=2.04, 95% CI 1.48-2.79) using no exposure as reference. There were significant positive relations between SHS exposure in general and depressive symptoms in a dose-response manner. These significant trends were observed consistently whether SHS exposure occurred in homes or workplaces. Our findings suggest that long-term and regular SHS exposure is associated with a significant, dose-dependent increase in risk of depressive symptoms.