Speciated fine particulate matter and self-reported sleep time in middle-aged and older Chinese adults: Single- and multi-pollutant approaches.

OBJECTIVE: This study aimed to explore the independent and joint associations of fine particulate matter (PM2.5) constituent exposure with total sleep time, the sum of nocturnal sleep and daytime napping duration, among middle-aged and older Chinese adults. METHODS: We explored how intermediate- (6-mth) and long-term (2-yr) PM2.5 and its five key chemical constituents-black carbon (BC), organic matter (OM), sulfate (SO42-), nitrate (NO3-), and ammonium (NH4+)-relate to total sleep time, with additional analyses for nocturnal sleep duration. Data were obtained from 19,505 middle-aged and older adults (≥45 years) in the CHARLS cohort during 2011-2018. Ambient PM2.5 constituent exposures were estimated using the Tracking Air Pollution in China dataset, while sleep metrics were collected via standardized questionnaires. We utilized linear mixed-effects models and quantile g-computation to assess single-constituent associations as well as combined impacts of the PM2.5 mixture. RESULTS: In intermediate- and long-term exposure, NO3-, SO42-, and NH4+ showed the most consistent and pronounced positive associations with total sleep time. Specifically, the results of fully adjusted models demonstrated that compared with the reference quartile, the highest quartile of intermediate-term exposure to PM2.5, BC, OM, SO42-, NO3-, and NH4+ increased total sleep time by 0.16 (95% Confidence Interval [CI]: 0.09-0.22), 0.08 (95% CI: 0.02-0.15), 0.08 (95% CI: 0.01-0.14), 0.17 (95% CI: 0.10-0.23), 0.14 (95% CI: 0.08-0.20), and 0.13 (95% CI: 0.08-0.19) h, respectively. The weight coefficient of SO42-, NO3-, and NH4+ was relatively larger compared with other PM2.5 constituents in the qgcomp models. Vulnerable subgroups included female, older participants, rural residents and individuals with pension. CONCLUSION: Intermediate- and long-term exposure to PM2.5 constituents correlated inversely with nocturnal sleep duration and positively with total sleep time. Moving beyond overall PM2.5 mass, this work emphasizes the divergent health impacts induced by different chemical constituents.