Insulin resistance mediates the association between sleep duration and type 2 diabetes: Urban-rural evidence from a Chinese cohort study.

This study aimed to examine urban-rural disparities in the association between nighttime sleep duration and type 2 diabetes mellitus (T2DM) risk in middle-aged and older adults, with particular attention to the mediating role of insulin resistance. We conducted a prospective cohort study using data from the China Health and Retirement Longitudinal Study, including 2169 participants. Nighttime sleep was categorized as short (<7 hours), normal (7-9 hours), or long (>9 hours). Urban/rural status was defined by self-reported residence. Cox proportional hazards models assessed associations between sleep duration and T2DM risk, and mediation analysis quantified indirect effects via insulin levels. Short sleep was significantly associated with increased T2DM risk in both urban (hazard ratio = 1.88, 95% confidence interval: 1.70-2.06) and rural (hazard ratio = 1.50, 95% confidence interval: 1.36-1.64) participants, compared with normal sleep. Baseline fasting insulin level (proxy for insulin resistance) mediated 20.3% of the total effect. The higher incidence observed in urban participants may be partly attributable to environmental stressors such as noise and air pollution. Short nighttime sleep was associated with a higher T2DM risk, with stronger effects among urban residents. Insulin resistance partially mediates this association. Population-specific interventions that promote sleep hygiene, address urban environmental stressors, and enhance rural healthcare access are warranted.