Mental health disorders, cancer risk, and the mediating role of lifestyle behaviours in the CARTaGENE cohort study

Background: Mental health disorders are highly prevalent in the Canadian population and has been associated with cancer risk; however, previous findings in literature are inconsistent (1–4). This study aims to elucidate the relationship between mental health disorders and cancer risk, as well as explore the potential mediating effects of lifestyle behaviours. Methods: A cohort study was conducted with 34,571 participants aged 40-69 years from the province of Quebec. Depression was conceptualized from the PHQ-9, antidepressant use, and either a positive screen from PHQ-9 scores, antidepressant use, or self-report of physician diagnosis. Anxiety was defined using the GAD-7, and co-morbid depression and anxiety was assessed using the PHQ-9 and the GAD-7. Cox proportional hazards regression models were used to investigate the association between mental health exposures and risk of prostate, lung, and all cancers combined. Mediating effects of health behaviours were assessed using Baron and Kenny mediation criteria., then a Quasi-Bayesian/Monte Carlo approximation was used to obtain confidence intervals. Results: For risk of all cancers combined, there was a modest positive association with all mental health exposures, however none reached significance with full adjustment. No relationships reached significance for prostate cancer. There were positive associations between mental health disorders and lung cancer risk, but only anxiety and lung cancer in women was significant with full adjustment (HR = 1.67, 95% CI: 1.01-2.76). Women had consistently higher risk estimates than men for all cancer and lung cancer risk for the majority of exposures. Smoking status mediated the relationship between depression (PHQ-9) and lung cancer, anxiety and lung cancer, and co-morbidity and lung cancer by 27%, 18%, and 26%, respectively in women. In men, smoking status mediated 17% of the relationship between depression (PHQ-9, antidepressant use, or self-report of physician diagnosis) on all cancers. Conclusions: Positive associations were observed between mental health disorders and overall and lung cancer risk, however few relationships reached significance. Risk estimates were generally higher in women than in men, suggesting a differential risk. Smoking status mediated a significant proportion of the relationships between mental health disorders and cancer risk.