Long-term exposure to PM2.5 constituents in relation to glucose levels and diabetes in middle-aged and older Chinese

Background: Previous studies have indicated the associations between fine particulate matter (PM2.5) exposure and diabetes or glucose levels. However, evidence linking PM2.5 constituents and diabetes or glucose levels was extensively scarce, particularly in developing countries. This study aimed to investigate the associations of exposure to PM2.5 and its five constituents (black carbon [BC], organic matter [OM], nitrate [NO3-], sulfate [SO42-], and ammonium [NH4+]) with diabetes and glucose levels among the middle-aged and elderly Chinese populations. Methods: A national cross-sectional sample of participants aged 45+ years was enrolled from 28 provinces across China’s mainland. Health examination and questionnaire survey for each respondent were performed during 2011−2012. Diabetes was determined by alternative definitions, and the main definition (MD) was self-report diabetes or antidiabetic medicine use or HbA1c ≥6.5 or fasting glucose ≥7 mmol/L or random glucose ≥11.1 mmol/L. Monthly exposure to PM2.5 mass and its five constituents (BC, OM, NO3-, SO42-, and NH4+) for each participant at residence were estimated using satellite-based spatiotemporal prediction models. Generalized linear models and linear mixed-effects models were used to assess the effects of exposure to PM2.5 and its constituents on diabetes or glucose levels, respectively. Stratification analyses were done by sex and age. Results: We included a total of 17,326 adults over 45 years in this study. The 3-year mean (interquartile range [IQR]) concentrations of PM2.5, BC, OM, NO3-, SO42-, and NH4+ were 47.9 (27.4) µg/m3, 2.9 (2.2) µg/m3, 9.2 (6.6) µg/m3, 10.2 (9.4) µg/m3, 11.0 (5.2) µg/m3, and 7.1 (4.4) µg/m3, respectively. Per IQR rise in exposure to PM2.5 was significantly associated with an increase of 0.133 mmol/L (95% confidence interval, 0.048−0.219) in glucose concentrations. Similar positive associations were observed for BC (0.097 mmol/L [0.012−0.181]), OM (0.160 mmol/L [0.065−0.256]), NO3- (0.145 mmol/L [0.039−0.251]), SO42- (0.111 mmol/L [0.026−0.196]), and NH4+ (0.135 mmol/L [0.041−0.230]). Under different diabetes definitions, PM2.5 mass and selected constituents with the exception of SO42- were all associated with a higher risk of prevalent diabetes. In MD-based analysis, similar positive associations were observed for four constituents, with corresponding odds ratios of 1.180 (1.097−1.270) for PM2.5, 1.154 (1.079−1.235) for BC, 1.170 (1.079−1.270) for OM, 1.200 (1.098−1.312) for NO3-, and 1.123 (1.037−1.215) for NH4+. Stratified analyses showed a significantly higher risk of diabetes in males (1.225 [1.064−1.411]) than females (1.024 [0.923−1.136]) when exposed to PM2.5. Participants under 65 years were generally more vulnerable to diabetes hazards related to PM2.5 constituents exposure. Conclusions: Exposures to PM2.5 and its constituents (i.e., BC, OM, NO3-, and NH4+) were positively associated with increased risks of prevalent diabetes and elevated glucose levels in middle-aged and older adults.