Secondhand Smoke Exposure and Depressive Symptoms Among Nonsmokers in China

Secondhand smoke exposure (SHSE) remains widespread in China and may be linked to mental health outcomes, yet evidence among older adults is limited. We examined the association between SHSE and depressive symptoms in a large cohort of nonsmoking older Chinese adults.

We conducted a cross-sectional analysis of 7958 nonsmoking participants aged 50 years or older from the Guangzhou Biobank Cohort Study. SHSE was assessed through structured interviews and quantified as cumulative exposure (in years at 40 h/week) and by context (home and workplace). Depressive symptoms were measured using the 15-item Geriatric Depression Scale (GDS-15). Linear regression models were used to examine associations between SHSE and GDS-15 scores, adjusting for age, sex, education, occupation, income, physical activity, and alcohol use.

Higher cumulative SHSE was associated with greater depressive symptom severity. Participants with more than 5 years of exposure had significantly higher GDS-15 scores than those with less than 2 years (adjusted β 0.21, 95% CI 0.09-0.32; p < 0.001). Workplace exposure was independently associated with higher GDS-15 scores (β 0.23, 95% CI 0.08-0.38), while the association for home exposure was weaker and nonsignificant after adjustment. A greater number of smokers and higher frequency of SHSE at home were also linked to elevated GDS-15 scores. No associations were observed with childhood exposure.

Among older nonsmoking adults, prolonged SHSE, particularly in workplace settings, showed a positive association with depressive symptom severity, although the direction of this association cannot be determined. These cross-sectional associations warrant investigation in prospective studies to determine whether SHSE exposure precedes depression onset and whether the relationship is causal or reflects shared risk factors.