Ambient ozone exposure and depression among middle-aged and older adults: Nationwide longitudinal evidence in China

Epidemiological studies have linked long-term ozone (O₃) exposure with depression in developed countries. However, available literature is sparse and exists great heterogeneities. We aimed to investigate the association of long-term O₃ exposure with depression among Chinese middle-aged and older adults.

We designed a repeated measurement study based on longitudinal data from four waves (2011, 2013, 2015, and 2018) of the China Health and Retirement Longitudinal Study (CHARLS). Annual mean O₃ concentrations assessed through machine learning-based spatiotemporal models were assigned to each participant at city level. Depression score was measured using the 10-item Center for Epidemiologic Studies Depression scale (CES-D-10), with scores above the cut-off point of ten defined as depressive symptom. Mixed-effects models were used to evaluate the impact of O₃ on depression score and depressive symptom, and quantify the concentration-response (C-R) relationships. Subgroup analyses were performed to examine the potential effect modifications.

A total of 19,582 participants with 60,125 visits were included in our analysis, with mean depression score of 8.1 (standard deviation: 6.3). Multivariable-adjusted mixed-effects model estimated a 6.34% (95% confidence interval [CI]: 3.34%, 9.43%) increase in depression score and an odds ratio (OR) of 1.29 (95% CI: 1.16, 1.45) for depressive symptom associated with per 10-μg/m³ rise in annual mean O₃ exposure. Significantly elevated risks were identified only at high concentrations (approximately ≥90 μg/m³). Participants who suffered from chronic diseases had a significant increased risk of depression (% Change in depression score: 8.42% [95% CI: 4.79%, 12.17%], and OR: 1.42 [95% CI: 1.24, 1.62]), and an evident effect modification was identified for depressive symptom (P = 0.01).

Our study provided novel evidence that long-term O₃ exposure could be a risk factor for depression among Chinese middle-aged and older adults. Our findings may have significant implications for formulating policies in reducing disease burden of depression by controlling air pollution.