Long-term exposure to ambient air pollution and incidence of type 2 diabetes in an industrial contaminated area in Central Italy.

Emerging evidence links air pollution to metabolic dysfunction, including Type 2 diabetes (T2D). However, findings remain inconsistent, particularly in areas with complex environmental pressures. We investigated the association between long-term exposure to multiple ambient air pollutants (PM10, PM2.5, NO2, SO2, C6H6) and the incidence of T2D in River Sacco Valley (RSV), an area in Central Italy designated as a Site of National Interest (SIN) due to severe chemical contamination and air pollution. This retrospective cohort study included 392,133 residents aged ≥35 years in RSV and Frosinone province (2008-2018). Incident T2D cases were identified through administrative databases using a validated algorithm. Individual pollutant exposure was assigned at residential addresses using a dispersion model (1 × 1 km2 resolution). Exposure to critical industrial environments was also considered. Cox proportional hazards models estimated Hazard Ratios (HR) per 1 μg/m3 pollutant increase, adjusting for sex, municipality, socioeconomic status and proximity to industrial plants, River Sacco and SIN municipalities. Effect modification by sex was also evaluated. 31,556 T2D incident cases were identified. SO2 exposure was associated with T2D incidence (HR: 1.01; 95% CI: 1.00-1.02), particularly among women (HR 1.02; 95% CI: 1.01-1.04), suggesting sex-specific vulnerability. Unexpectedly, PM10, PM2.5 and C6H6 showed inverse associations, while NO2 was not linked to T2D. Notably, residing within 1 km from River Sacco consistently increased T2D risk. These findings may reflect local exposure patterns, residual confounding or the influence of β-hexachlorocyclohexane contamination near the river, highlighting the need for environmental health research in burdened areas to inform equitable prevention strategies.