Long-term exposure to fine particulate matter and its constituents is related to self-reported visual impairment among middle-aged and older adults: a longitudinal study in China

Visual impairment (VI) poses an increasing global health burden, yet the long-term effects of fine particulate matter (PM2.5) constituents on VI remain unclear. This study aimed to evaluate associations between long-term exposure to PM2.5 and its constituents and the risk of VI. We used data from the nationally representative China Health and Retirement Longitudinal Study (CHARLS, 2011–2018) including adults aged ≥ 45 years. Long-term exposure to PM2.5 and its constituents (SO42–, NO3–, NH4+, organic matter (OM), and black carbon (BC)) was obtained from the Tracking Air Pollution in China dataset and linked to participants’ residential cities. The 3-year moving average concentration was used as the primary exposure metric to capture cumulative effects, while the 1-year average concentration was applied for sensitivity analysis. VI was defined as self-reported fair or poor vision. Associations were estimated using time-dependent Cox models, with restricted cubic spline (RCS), stratified and interaction analyses to assess nonlinear and subgroup effects. Over 27,443 person-years of follow-up, 3,736 participants developed VI. Per interquartile range (IQR) increase in 3-year moving average concentrations, higher risks of VI were observed for PM2.5 (HR = 1.09, 95% CI: 1.03–1.15), SO42– (HR = 1.13, 95% CI: 1.05–1.22), NO3– (HR = 1.06, 95% CI: 1.00–1.13), NH4+ (HR = 1.09, 95% CI: 1.02–1.17), OM (HR = 95% CI: 1.15, 1.07–1.24), and BC (HR = 1.24, 95% CI: 1.14–1.34). RCS analysis revealed non-linear associations for PM2.5, NO3–, NH4+, and OM, whereas SO42– and BC showed approximately linear trends. Associations were more pronounced among older adults (> 60 years old), smokers, and those with hypertension. Long-term exposure to PM2.5 and its constituents significantly increases the risk of VI among middle-aged and older adults in China, highlighting the need for targeted environmental health policies.