Long-term Exposure to Fine Particulate Matter Constituents and Cognitive Impairment Among Older Adults: An 18-year Chinese Nationwide Cohort Study

Background: Although growing evidence has shown independent links of long-term exposure to fine particulate matter (PM) with cognitive impairment, the effects of its constituents remain unclear. This study aims to explore the associations of long-term exposure to ambient PM constituents' mixture with cognitive impairment in Chinese older adults, and to further identify the main contributor.

Methods: 15,274 adults ≥ 65 years old were recruited by the Chinese Longitudinal Healthy Longevity Study (CLHLS) and followed up through 7 waves during 2000-2018. Concentrations of ambient PM and its constituents (i.e., black carbon [BC], organic matter [OM], ammonium [NH], sulfate [SO], and nitrate [NO]) were estimated by satellite retrievals and machine learning models. Quantile-based g-computation model was employed to assess the joint effects of a mixture of 5 PM constituents and their relative contributions to cognitive impairment. Analyses stratified by age group, sex, residence (urban vs. rural), and region (north vs. south) were performed to identify vulnerable populations.

Results: During the average 3.03 follow-up visits (89,296.9 person-years), 4294 (28.1%) participants had developed cognitive impairment. The adjusted hazard ratio [HR] (95% confidence interval [CI]) for cognitive impairment for every quartile increase in mixture exposure to 5 PM constituents was 1.08 (1.05-1.11). BC held the largest index weight (0.69) in the positive direction in the qg-computation model, followed by OM (0.31). Subgroup analyses suggested stronger associations in younger old adults and rural residents.

Conclusion: Long-term exposure to ambient PM, particularly its constituents BC and OM, is associated with an elevated risk of cognitive impairment onset among Chinese older adults.