Associations of outdoor artificial light at night with type 2 diabetes and metabolic syndrome among Chinese adults

Abstract

This study investigated the associations between outdoor artificial light at night (ALAN) and type 2 diabetes (T2DM) and metabolic syndrome (MetS) and aimed to characterize the dose-response relationships and potential exposure thresholds. This cross-sectional study included 57,898 Chinese adults who underwent health examinations in Hubei, China, from January 2013 to June 2025 in T2DM analysis. A subset of 25,735 participants with complete data was analyzed for MetS. ALAN exposure was estimated using satellite-derived nighttime light intensity (NPP‑VIIRS‑like data) within a 500 m radius of each residence. Multivariable logistic regression models estimated odds ratios (ORs) and 95% confidence intervals (CIs), adjusting for age, gender, education, marital status, income, smoking, and alcohol consumption. Generalized additive models (GAMs) and two‑piecewise regression models were applied to examine nonlinearity and threshold effects. Higher ALAN exposure was associated with increased odds of T2DM (OR = 1.68, highest vs. lowest quartile) and MetS (OR = 1.20). Nonlinear, threshold-type dose–response relationships were identified, with threshold ranges of 28.05–50.97 nW/cm²/sr for T2DM and 23.31–50.17 nW/cm²/sr for MetS. Associations appeared strongest for T2DM among adults older than 45 years and for MetS among adults older than 60 years. In gender-stratified analyses, associations with MetS were more pronounced in male participants, although the interaction tests were not statistically significant. Overall, outdoor ALAN exposure was associated with higher odds of T2DM and MetS in a nonlinear, threshold-dependent manner. These findings suggest that outdoor ALAN may be a potentially modifiable environmental factor associated with the prevalence of metabolic diseases, particularly among older adults.