Associations of long-term exposure to PM2.5 and its chemical constituents with incident visual impairment risk: A cohort study of 12 million school students.

BACKGROUND: Visual impairment among children and adolescents is a major public health concern. However, evidence regarding the associations of PM2.5 and its chemical constituents with incident visual impairment remains limited, particularly in highly polluted regions. We aimed to investigate these associations in northern China. METHODS: This study included 12,433,993 school students from a dynamic cohort in Shandong Province, China, followed from 2012 to 2024. Annual concentrations of PM2.5 and its five major chemical constituents were estimated using data from the Tracking Air Pollution in China database. Visual impairment was defined as visual acuity below 4.9 in either eye. Cox proportional hazards models were used to estimate associations, with penalized splines characterizing exposure-response relationships. Quantile g-computation assessed the joint association of the five constituents. RESULTS: During 35,156,004 person-years of follow-up, 8,036,370 participants (64.6%) developed visual impairment. Each IQR increase in PM2.5 concentration was associated with a 58% higher risk of incident visual impairment (HR, 1.58; 95% CI, 1.53-1.63), while the five constituents were also positively associated with incident visual impairment (HRs: 1.53-1.57). PM2.5 and all five chemical constituents showed predominantly non-threshold linear or supra-linear exposure-response relationships. A simultaneous one-quartile increase in all five constituents was associated with a 26% higher risk of incident visual impairment (HR, 1.26; 95% CI, 1.24-1.28). Stronger associations were consistently observed among students in higher grades. CONCLUSIONS: Our findings provide evidence of the adverse associations of PM2.5 and its chemical constituents with visual impairment risk and emphasize the need for more rigorous regulations targeting these pollutants in China.