Underweight and cardiovascular risk in Type 2 diabetes: a Korean nationwide study

Background and Aims With the growing prevalence of lean Type 2 diabetes mellitus (T2DM) and limited research on stratified underweight categories, this study investigated the association between underweight status and cardiovascular disease (CVD) risk in T2DM patients, focusing on the impact of underweight severity. Methods A nationwide cohort study analysed data from 2 064 406 adults with T2DM who underwent health examinations between 2015 and 2016, sourced from the Korean National Health Insurance Service database. Participants were classified by body mass index into underweight, normal weight, overweight, and obesity, with underweight further stratified into mild (17–18.4 kg/m2), moderate (16–16.9 kg/m2), and severe (<16 kg/m2). Primary outcomes were CVDs, including myocardial infarction and ischaemic stroke, assessed using Cox proportional hazards models adjusted for demographic, clinical, and lifestyle factors. Results During a mean follow-up of 5.7 years, 111 522 CVD events, including 55 622 MI and 62 099 ischaemic stroke events, were documented. Compared with the normal weight group, all underweight groups showed significantly higher CVD risks (adjusted hazard ratio [95% confidence interval]: 1.49 [1.28–1.73], 1.47 [1.33–1.63], and 1.19 [1.13–1.25] for severe, moderate, and mild underweight, respectively). These risks exceeded those for body mass index ≥ 35 kg/m2 (1.14 [1.08–1.22]), showing a reverse J-shaped association. Stratified analyses indicated stronger associations in younger individuals and non-smokers. Conclusions Underweight status in T2DM patients is significantly associated with increased risk of CVDs, particularly in those severely underweight, exceeding the risks observed with obesity. These findings emphasize the need for dedicated guidelines for managing underweight T2DM patients to mitigate cardiovascular risks.