Association of Body Mass Index and Its Change With Incident Diabetes Mellitus.

Context: There have been insufficient data on the threshold of body mass index (BMI) for developing diabetes mellitus (DM) and the relationship between change in BMI and the subsequent risk of DM.

Objective: We sought to clarify the association of BMI and its change with incident DM.

Methods: We conducted a retrospective observational cohort study using the JMDC Claims Database between 2005 and 2021. We included 3 400 303 individuals without a prior history of DM or usage of glucose-lowering medications. The median age was 44 years, and 57.5% were men. We categorized the study participants into 4 groups: underweight (BMI < 18.5 kg/m2), normal weight (BMI 18.5-24.9 kg/m2), overweight (BMI 25.0-29.9 kg/m2), and obese (BMI ≥ 30 kg/m2). According to the change in BMI from the initial health check-up to the health check-up 1 year after that, we divided the study participants into 3 groups: ≤-5.0%, -5.0% to +5.0%, and ≥+5.0%.

Results: The risk of developing DM increased steeply after BMI exceeded approximately 20 to 21 kg/m2. Compared with participants with stable BMI (-5.0% to +5.0%), the relative risk for DM among those whose BMI had increased by 5.0% or more was 1.33 (95% CI 1.31-1.36). In contrast, the relative risk for DM among those whose BMI decreased by 5.0% or more was 0.82 (95% CI 0.80-0.84). Moreover, people classified as normal weight, overweight, and obese reduced the risk of developing DM when they reduced their BMI, whereas the risk of developing DM for people classified as underweight increased when they reduced their BMI.

Conclusion: Our findings offer novel insights into improving an optimal bodyweight management strategy to prevent the development of DM.