AI Insight
A retrospective cohort study of 64,970 Japanese adults aged 40 to 74 years found a U-shaped relationship between body mass index and kidney function decline, defined as a 30 percent or greater reduction in estimated glomerular filtration rate over two years. Both obese individuals (BMI 30.0 to 39.9 kg/m2) and underweight individuals (BMI 14.0 to 18.9 kg/m2) showed approximately twice the odds of kidney function decline compared to the reference group, after adjusting for multiple confounders including blood pressure, HbA1c, and lipid profile. These findings suggest that kidney health risk at the population level is not limited to obesity but extends to individuals at the lower end of the BMI spectrum.
Why it matters
Japan faces one of the highest rates of dialysis dependence globally, and these results indicate that public health screening and preventive guidance should be directed at both obese and underweight individuals, not solely those with excess body weight. Identifying underweight status as a comparable risk factor could prompt revisions to chronic kidney disease prevention strategies in aging populations.
by Miki Nakamura, Chiho Yamazaki, Keiju Hiromura, Atsushi Goto, Kei Hamazaki
Japan has one of the highest dialysis prevalence rates worldwide, resulting in substantial economic and health burdens. Although obesity is a known risk factor for the decline of kidney function, the impact of being underweight remains unclear. This study aimed to investigate the relationship between body mass index (BMI), including underweight status, and kidney function decline using health check-up data. We conducted a retrospective cohort study involving Japanese individuals aged 40–74 years in Gunma Prefecture who underwent health checkups in fiscal years 2018 and 2020. The exposure was baseline BMI, which was classified into seven categories. The primary outcome was kidney function decline, defined as a ≥ 30% reduction in estimated glomerular filtration rate (eGFR) over a two-year period. Associations between BMI and kidney function decline were assessed using multivariable logistic regression analysis, adjusting for age, sex, smoking status, alcohol consumption, blood pressure, hemoglobin A1c, lipid profile, and baseline eGFR. A total of 64,970 individuals were included in the final analysis. A U-shaped association was observed between BMI and decline in kidney function. Compared to the reference group, those with obesity (BMI = 30.0–39.9 kg/m²; odds ratio [OR]: 2.05; 95% confidence interval [CI]: 1.31–3.19) and those underweight (BMI = 14.0–18.9 kg/m²; OR: 2.09; 95% CI: 1.43–3.04) had significantly increased risk. The U-shaped association between BMI and kidney function decline suggests that both obesity and underweight status are risk factors. Health guidance should target individuals in both categories to prevent chronic kidney disease.