Frailty mediated the associations of fine particulate matter with depression and anxiety: Findings from the UK Biobank.

Background: The role of frailty in the associations of fine particulate matter (PM2.5) with depression and anxiety was unknown.

Methods: This study is a longitudinal population-based cohort study. A total of 444,094 UK Biobank participants without depression or anxiety at baseline were included. PM2.5 concentrations and frailty phenotype were measured at baseline, while incident depression and anxiety were identified during a median follow-up of 7.8 years. A multivariable cox regression model was utilized to evaluate the prospective relationships between PM2.5/frailty and the risk of depression and anxiety. Mediation analyses were performed to examine whether the associations were mediated by frailty.

Results: Both frailty and PM2.5 exposure were associated with a higher risk of depression and anxiety. Each 10 ug/m3 increase in PM2.5 was associated with a 33% and 42% higher risk of depression (HR 1.33, 95%CI: 1.17-1.49) and anxiety (HR 1.42, 95%CI: 1.24-1.67), respectively. Compared with individuals with non-frailty, those with frailty was associated with a higher risk of depression (HR 3.14, 95%CI: 3.01-3.28) and anxiety (HR 2.39, 95%CI: 2.28-2.52), respectively. The estimate of the nature indirect effects (NIEs) of frailty were 1.07 (95%CI: 1.06-1.09) and 1.05 (95%CI: 1.05-1.06), which accounted for 64.6% and 22.4% of the associations between PM2.5 and depression/anxiety, respectively.

Conclusion: Our findings suggest that both exposure to PM2.5 and frailty are associated with higher risk of depression and anxiety. The adverse associations between PM2.5 and depression/anxiety are partially mediated through frailty. Targeting frailty management could be a critical strategy for reducing the PM2.5-related psychiatric health burden.