Single and joint associations of physical activity and depression with risk of all-cause mortality: a prospective cohort study of NHANES data.

BACKGROUND: Depression and physical activity (PA) are interrelated elements crucial to human health. However, the evidence regarding the relationship between depression, PA, and mortality remains limited. OBJECTIVE: To estimate the single and joint associations PA and depression on mortality risk, and further examine whether PA moderates the association between depression and mortality. METHODS: Data were from the National Health and Nutrition and Examination Survey (NHANES) conducted between 2007 and 2018 and linked to the National Death Index death certificate records. Depression status was determined by the 9-item Patient Health Questionnaire (PHQ-9) and PA levels were measured by self-reporting activity (type, metabolic equivalent (MET) and time per week). Kaplan-Meier method and Cox proportional hazards models were applied to explore the single and joint associations between depression and PA with all-cause mortality. RESULTS: A total of 26,150 participants were enrolled, of whom 9.2% (n = 2412) died during follow-up (median 81 months), 29.9% (n = 7810) met the PA recommendation and 9.2% (n = 2416) suffered from depression (scored ≥ 10 on the PHQ-9). For the single association, depression (HR 1.40, 95% CI 1.16-1.69, serious depression vs. no) was positively associated with mortality, but the association of PA (HR 0.66, 95% CI 0.58-0.76, regular PA vs. physically inactive) was inverse. Joint association analyses showed that the association between depression and mortality was influenced by PA, whereas more frequent PA was associated with lower mortality risk irrespective of the level of depression symptoms: compared to participants who were depressed and did not participate in PA, those who did participate in PA, whether depressed or not, had a lower risk of death. Especially, for participants who were moderately depressed and did not PA, both insufficient PA (HR, 0.43; 95% CI, 031-0.61) and regular PA (HR, 0.37; 95% CI, 0.24-0.58) significantly reduced the risk of all-cause mortality. CONCLUSIONS: Our study found that depression was positively associated with increased mortality risk, while PA was negatively associated with it; moreover, the mortality risk associated with depression worsened with low levels of physical activity. These findings underscore the critical importance of promoting physical activity, especially among individuals with depression, as a potential strategy to mitigate mortality risk. This highlights the need for integrated public health interventions that address both mental health and physical activity to improve overall population health outcomes.