Objective: Previous population-based studies suggest that exposure to secondhand smoke (SHS) is related to increased depressive symptoms and poor mental health among non-smokers. We examined whether these associations could be replicated in two independent Dutch samples.
Methods: Non-smoking adults were selected from two studies: 1) the Netherlands Study of Depression and Anxiety (NESDA), comprising individuals with current and remitted depressive and/or anxiety disorders, and healthy controls and 2) the Netherlands Twin Register (NTR), comprising twin-family studies on health-related behaviors. In both studies, SHS exposure was assessed with plasma cotinine levels (1-14ng/ml vs. <1ng/ml). In NESDA, outcomes were current depressive and/or anxiety disorders, and depression and anxiety symptom severity scores. In NTR, the Adult Self Report derived DSM-subscales for depressive and anxiety problems, and anxious depressive scores were analyzed.
Results: In NESDA non-smokers (n=1757), increased plasma cotinine level (≥1ng/ml) was not related to current depressive and/or anxiety disorders [odds ratio (OR) 0.96, P=.77], nor to depression or anxiety severity indicators. Similarly, in NTR non-smokers (n=1088) cotinine levels ≥1ng/ml were not associated with the DSM-subscale for depressive problems [unstandardized regression coefficient (B) 0.04, P=.88], nor to other depression and anxiety measures.
Conclusions: In non-smoking adults from patient and population samples, we found no evidence that plasma cotinine levels were related to either depressive and/or anxiety disorders, or to depressive and anxiety symptoms. This suggests that SHS exposure is not related to depression and anxiety in non-smoking adults.
Keywords: Anxiety; Cotinine; Depression; Passive smoking; Secondhand smoke.