Association between urine cotinine and depressive symptoms in non-smokers: National representative sample in Korea

Secondhand smoke (SHS) exposure is known to have negative effects on mental as well as physical health. However, the association between SHS and mental health problems has not been assessed in non-smokers. To evaluate the association of exposure to tobacco smoke and depressive symptoms, and that of the prevalence of having depressive symptoms and urinary cotinine (UCo) concentrations in non-exposed subjects.

Data was extracted from the Korea National Health and Nutrition Examination Survey (KNHANES). Depressive symptoms were determined based on a patient's overall score on the Patient Health Questionnaire (PHQ)-9, and SHS exposure was evaluated using self-reported data and UCo concentration. Overall, 13,219 non-smokers, ≥ 19 years were included in the study. Multinomial logistic regression analysis was conducted to identify factors related to depressive symptoms; independent t-test was conducted to confirm the differences in UCo concentration according to the prevalence of depression.

Among the non-exposure groups, 2.0% of the males and 5.6% of the females showed depressive symptoms. Lower social-economic status, higher UCo concentration, and SHS exposure increased the prevalence of depressive symptoms. The UCo concentration of females with depressive symptoms was significantly higher than those of females without depressive symptoms.

This study only demonstrated an association between SHS exposure and depression, not the causal effects, because of the cross-sectional study design.

SHS exposure and depressive symptoms are correlated. The association was also confirmed by evaluating the UCo concentration of those who were not exposed to SHS based on self-reported data.