Beneficial Body Mass Index for Age-Related Kidney Function in Males and Females

Kidney function declines with aging, leading to a high prevalence of age-related disease. Concurrently, the increasing prevalence of overweight and obesity may influence age-related kidney changes. This study aims to clarify the relationship between body mass index (BMI) and kidney function in the Chinese population, with a focus on sex differences.

We conducted a retrospective cross-sectional study involving 343,040 Chinese adults, stratified by sex and age. Glomerular filtration rate (GFR) was estimated using the CKD-EPI formula based on serum creatinine. We examined trends in BMI and its distribution across age groups, as well as the patterns of estimated GFR (eGFR) decline within BMI subgroups. Multi-linear and multi-logistic regression analyses were used to assess the association between BMI and age-related kidney function.

BMI levels and categories varied with age, exhibiting sex-specific patterns. Overweight and obese individuals experienced a more pronounced decline in eGFR, except for females under 45. In males, BMI showed a negative correlation with eGFR, while females under 65 exhibited a positive association; older females showed a negative correlation. Significant risks for mildly reduced kidney function were noted in overweight or obese males and older females, with no risk identified in younger females.

A normal BMI (18.5-25 kg/m²) is associated with better age-related kidney function in all-aged males and females older than 45 years, considering eGFR levels and decline rates.