Loss of life expectancy attributed to long-term ozone exposure in Chinese older adults: Cross-cohort analysis from 3 national cohorts

Abstract

Background

Cohort evidence linking ozone (O₃) exposure with mortality was sparsely investigated among the elderly in low- and middle-income countries. This study aims to quantify mortality risk and burden attributed to chronic O₃ exposure in Chinese older adults.

Methods

A total of 30,874 older adults aged ≥ 65 years were recruited from 3 national dynamic cohorts across 29 provincial regions in China, 2005–2018. Annual warm-season (April–September) O₃ and year-round PM_2.5 concentrations were estimated through well-validated satellite-based spatiotemporal models and were assigned to participants for each survey year. Time-dependent Fragility Cox models with random intercept for study cohort were employed to quantify O₃-mortality association, adjusting for demographic, behavioral, health, and environmental covariates. A counterfactual causal framework was used for assessment of O₃-attributable premature deaths in older adults based on exposure–response relationship derived from multi-cohort two-pollutant analysis (+PM_2.5). Years of life lost and loss of life expectancy were subsequently evaluated based on the burden estimation model by incorporating the comparative risk assessment method and reference life tables.

Results

16,939 death events occurred during 0.16 million person-years of follow-up surveys. Each 10-ppb increase in O₃ exposure was linked with a hazard ratio of 1.076 (95 % confidence interval [CI]: 1.050, 1.102) for all-cause mortality. By achieving the counterfactual target (WHO AQG 2021) of 60 μg/m³ for warm-season O₃, 0.88 (95 % CI: 0.60, 1.14) million premature deaths could be avoidable among Chinese older population in 2019, yielding an inconspicuous reduction of 0.11 million compared to the estimate in 2011 (0.99 million, 95 % CI: 0.68, 1.28). O₃-attributable deaths amounted to 9.05 (95 % CI: 6.19, 11.70) million years of life lost in 2019, equivalent to a loss of life expectancy of 0.93 (95 % CI: 0.63, 1.20) years for older population in China.

Conclusions

Our multi-cohort analysis suggested that reducing ambient O₃ exposure could effectively increase the life expectancy of Chinese older adults, which may contribute to the development of healthy aging strategies and national cleaning air policies.