Combined impact of diabetes mellitus and substance use on injury risk: a nationwide population-based cohort study in Taiwan

This study aimed to examine the independent and combined impacts of diabetes mellitus (DM), and substance use on the risk of accidental injuries in a nationwide population-based cohort in Taiwan. Using Taiwan’s National Health Insurance Research Database (NHIRD), two retrospective cohorts were analyzed. The DM cohort (2000–2013) included 31,424 patients with DM and 94,272 age-, sex-, and index-year-matched controls. The substance uses cohort (2013–2022) included 324,648 substance users and an equal number of matched controls. Injury outcomes were classified as traffic accidents, falls, burns and fires, brain injuries, suicide, and drowning. Cox proportional hazards models were applied to estimate adjusted hazard ratios (aHRs) with 95% confidence intervals (CIs), and Kaplan–Meier analyses were used for descriptive visualization of cumulative injury risk, and interaction was formally assessed using Cox regression models. Patients with DM exhibited a 1.702-fold higher risk of injury compared to non-DM individuals, while substance users demonstrated a 1.444-fold higher risk compared to non-users. Among substance users, the highest risks were found for suicide (aHR = 10.287), intentional injury (aHR = 2.453), and falls (aHR = 1.742). Female sex, low income, major illness, and comorbidities (stroke, hypertension, hyperlipidemia) further amplified injury risk. Both DM and substance use were independently associated with increased injury risk. In joint-effects analyses, individuals with both DM and substance use had the highest injury risk among the four exposure groups (non-DM/non-user, DM only, substance use only, and DM + substance use). The multiplicative interaction between DM and substance use was statistically significant. Results were consistent in sensitivity analyses restricted to unintentional injuries. DM and substance use independently elevate the risk of accidental and intentional injuries; their coexistence is associated with the highest injury risk that markedly increases injury susceptibility. Integrating chronic disease management with substance use prevention and behavioral interventions may reduce injury-related morbidity and mortality in high-risk populations.