Impact of a History of Obesity on Diabetic Microvascular Complications in Patients with Type 2 Diabetes

Background/Objectives: The prevalence of obesity is increasing among Japanese patients with type 2 diabetes (T2D); however, the impact of obesity history and severity on microvascular complications remains poorly understood. This study aimed to investigate the association of lifetime maximum body mass index (BMI) and BMI at the first clinical visit with the development and progression of diabetic nephropathy and retinopathy. Methods: This retrospective cohort study included T2D patients who first visited the clinic of the Institute for Medical Sciences, Asahi Life Foundation between 2005 and 2022. Patients were categorized into five groups based on both lifetime maximum and first-visit BMI: underweight, normal weight, class I obesity, class II obesity, and severe obesity. The primary endpoints were renal events (sustained increase in proteinuria or ≥40% decline in eGFR) and retinal events (worsening of diabetic retinopathy by ≥1 stage). Results: A history of severe obesity, based on the lifetime maximum BMI, was an independent risk factor for proteinuria progression. While a history of severe obesity was associated with all endpoints in unadjusted analyses, these associations with eGFR decline and retinopathy were not significant after adjusting for covariates. In contrast, the BMI at the first visit was significantly associated with retinal events but not with renal events. Conclusions: A history of maximum lifetime obesity is a critical predictor of the proteinuria progression. A history of obesity, a simple clinical metric, is a valuable tool for identifying high-risk patients and may contribute to more effective preventative strategies.