Obesity Paradox: BMI is Inversely Associated with the Risk of HIP Fracture in Elders with Type 2 Diabetes

Background: Taiwan has the fastest aging population in the world. Thus, osteoporosis and related fractures have increasingly become some of the most challenging disorders that threaten Taiwan older persons. Hip fractures cause considerable adverse outcome and excess mortality, posing a growing and major burden on health care. Low body weight is confirmed a risk factor for osteoporotic fractures in general population. However, epidemiological studies on the risk of hip fracture among type 2 diabetic patients were limited. The aim of the study was to explore the association between body mass index (BMI) and the risk of hip fracture in elders with type 2 diabetes. Methods: We conducted a retrospective cohort study on 20,590 type 2 diabetes elders who participated in the National Diabetes Case Management Program in Taiwan. BMI at baseline and hip fracture events over the 7.75 years were analyzed. Results: The incidence rates of hip fracture were 12.86, 9.57, 806, and 7.39 per 1000 person-years in groups of the ＜18.5, 18.5-24, 24-27, and 27 kg/m2 of baseline BMI, respectively. After multivariate adjustment, the risk of hip fracture was decreased among patients with BMI levels of ≥27 kg/m^2 compared with patients with BMI levels 18.5-24 kg/m^2 [hazard ratio (HR): 0.85, 95% confidence interval (CI): 0.74-0.97]. Significant linear trends across different BMI levels were observed (p＜0.009). Conclusions: Patients categorized as BMI greater than 27 kg/ m^2 exhibited a decreased risk of hip fracture, confirming an inversely relationship. The beneficial effect of BMI on hip fracture is supported by the findings of previous studies indicated that body weight exerts a positive effect of mechanical loading on bone formation.