PM2.5 and temperature exposure and type 2 diabetes mellitus hospitalization risk: A 15-year multicenter study in subtropical monsoon regions

Objective To investigate the independent and combined effects of short-term exposure to ambient fine particulate matter with aerodynamic diameter ≤ 2.5 μm (PM₂.₅) and temperature on hospitalization risk for type 2 diabetes mellitus (T2DM) in subtropical monsoon regions, and to identify susceptible populations and lagged effects. Methods This retrospective, multicenter time-series study included 882,728 T2DM hospitalization records among adults aged ≥18 years from 13 tertiary hospitals in Guangxi, covering 2010–2024. Daily city-level PM₂.₅ estimates were obtained from a validated public gridded air-pollution dataset and linked with meteorological data and daily hospitalization counts. Distributed lag non-linear models (DLNM) with quasi-Poisson regression were applied to estimate exposure–response relationships, with maximum lag periods of 14 days for PM₂.₅ and 28 days for temperature. Models were adjusted for long-term trends, seasonality, meteorological factors, co-pollutants, day of week, holidays, and the COVID-19 period. Sensitivity analyses were performed to evaluate model robustness. Results Moderately high temperatures (25.9–32.5 °C) were associated with lower T2DM hospitalization risk, whereas extremely low temperatures significantly increased risk after several days of lag. PM₂.₅ exposure elevated hospitalization risk in a lagged and cumulative manner, with the cumulative effect peaking at lag 14 days (relative risk (RR) = 1.004, 95% confidence interval (CI) = 1.002–1.007). Associations were significant only among individuals aged ≤60 years. Synergistically increased risk was observed for combined exposure to low temperature and high PM₂.₅. Conclusions Short-term PM₂.₅ exposure significantly increases T2DM hospitalization risk, especially in people aged ≤60 years, with delayed and cumulative effects. Low temperature and high PM₂.₅ further amplify risk. Targeted environmental and clinical interventions are warranted for susceptible populations in subtropical regions.