Exploring the relationship between secondhand smoke exposure in different indoor environments and depression symptoms among non-smoking adults: A cross-sectional study from NHANES.

Introduction: The existing evidence regarding the relationship between secondhand smoke (SHS) exposure and depression symptoms in non-smoking adults remains inconclusive. This cross-sectional study aims to further investigate this relationship using data from the National Health and Nutrition Examination Survey (NHANES).

Methods: SHS exposure was assessed through self-reported passive exposure to indoor tobacco products, such as those encountered at work or in vehicles. Depression symptoms were measured using the Patient Health Questionnaire-9 (PHQ-9) scale. Logistic regression and stratified analyses were conducted to evaluate the association between exposure to seven different indoor sources of SHS and depression symptoms.

Results: This study included 6272 never smoker adults from the US. Compared to individuals not exposed to any indoor SHS, exposure to specific types of SHS was positively associated with depression symptoms: exposure to cars (AOR=1.64; 95% CI: 1.17-2.31), exposure to other indoor areas (AOR=2.03; 95% CI: 1.33-3.10), and exposure to e-cigarettes (AOR=1.78; 95% CI: 1.14-2.77). When cumulative SHS exposure was calculated based on the number of SHS environments to which participants were exposed, those exposed to 1-2 sources of SHS were 1.47 times more likely (AOR=1.47; 95% CI: 1.13-1.91) and those exposed to ≥3 sources were 1.96 times more likely (AOR=1.96; 95% CI: 1.17-3.28) than unexposed individuals to experience depression symptoms.

Conclusions: Exposure to specific SHS environments, particularly simultaneous exposure to multiple SHS environments, seems to be significantly associated with depression symptoms among US adults. Establishing causality and understanding the health implications of this connection will require future longitudinal investigations.