The impact of body mass index on mortality according to age in hemodialysis patients: an analysis of the Korean Renal Data System

The impact of age on the relationship between body mass index (BMI) and all-cause mortality in hemodialysis (HD) patients is not clearly understood. Using data from the Korean Renal Data System (2001–2022), we analyzed 66,129 HD patients, stratified into young (<65 years, n = 24,589), younger-old (65–74 years, n = 17,732), and older-old (≥75 years, n = 23,808) groups. Patients were categorized into BMI quartiles, and survival outcomes were evaluated using Kaplan-Meier curves and event time ratios for the relative change in the survival time. During the follow-up period, 14,360 of the patients (21.7%) died, with a median follow-up of 3.4 years. Kaplan-Meier curves revealed poorer outcomes in lower BMI quartiles across all age groups. The lowest BMI quartile was significantly associated with a shorter survival time compared to the highest BMI quartile, with a 15% reduction in the young group (p = 0.001) and a 12% reduction in the older-old group (p = 0.002). Predicted survival time increases with rising BMI in the young group, but the rate of increase slows in the younger-old group and plateaus in the older-old group after a BMI of 25 kg/m². Lower BMI correlates with higher mortality, particularly in younger HD patients.