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.