We examine cross-sectional and prospective associations between objectively measured SHS exposure and mental health using data from the Health and Lifestyle Survey (HALS), a large, UK-wide, general population-based, prospective cohort study with measurements of carbon monoxide or salivary cotinine levels.

Mental health was assessed using the 30-item version of the General Health Questionnaire (GHQ). Multivariate logistic regression models adjusting for age, sex, height, body mass index, alcohol intake, social status, and longstanding illness were used to analyze the association between exposure to SHS (exhaled CO and salivary cotinine categories) and psychological distress (≥ 5 GHQ).

Fully adjusted cross-sectional analysis revealed a positive relationship between exhaled carbon monoxide and psychological distress among smokers (OR 1.36; 95% CI 1.04-1.78) but not among non-smoking adults. In a similar cross-sectional analysis between cotinine level and psychological distress, non-significant associations were found among smokers and non-smokers. Prospective analyses of the cotinine-psychological distress relationship among participants without psychological distress at baseline showed no significant increased risk of psychological distress among both smokers and non-smokers. In a prospective analysis of poor mental health outcome with respect to self-report smoking and SHS status, smokers had an increased risk of psychological distress while SHS and non-smokers did not.

A non-significant association between objectively measured SHS exposure and poor mental health was found in this study. Our findings show discrepancies with recent studies suggesting the need for additional future research in this growing field of study.