Soo Wan Kim

Background Underweight status increases the risk of cardiovascular disease and mortality in the general population. However, whether underweight status is associated with an increased risk of developing end‐stage kidney disease is unknown. Methods A total of 9 845 420 participants aged ≥20 years who underwent health checkups were identified from the Korean National Health Insurance Service database and analysed. Individuals with underweight (body mass index [BMI] < 18.5 kg/m 2 ) and obesity (BMI ≥ 25 kg/m 2 ) were categorized according to the World Health Organization recommendations for Asian populations. Results During a mean follow‐up period of 9.2 ± 1.1 years, 26 406 participants were diagnosed with end‐stage kidney disease. After fully adjusting for other potential predictors, the moderate to severe underweight group (<17 kg/m 2 ) had a significantly higher risk of end‐stage kidney disease than that of the reference (normal) weight group (adjusted hazard ratio, 1.563; 95% confidence interval, 1.337–1.828), and competing risk analysis to address the competing risk of death also showed the similar results (adjusted hazard ratio, 1.228; 95% confidence interval, 1.042–1.448). Compared with that of the reference BMI group (24–25 kg/m 2 ), the adjusted hazard ratios for end‐stage kidney disease increased as the BMI decreased by 1 kg/m 2 . In the sensitivity analysis, sustained underweight status or progression to underweight status over two repeated health checkups, when compared with normal weight status, had a higher hazard ratio for end‐stage kidney disease. Conclusions Underweight status is associated with an increased risk of end‐stage kidney disease, and this association gradually strengthens as BMI decreases.