Age-Stratified Analysis of the BMI-Kidney Stone Relationship: Findings from a National Cross-Sectional Study

Liuliu Zhou ^1* Wei Gu ^2* Yufeng Jiang ^3* Haimin Zhang ^4*

• ¹ School of Medicine, Tongji University, Shanghai, Shanghai Municipality, China
• ² Department of Nursing,Chongming Branch, Shanghai Tenth People’s Hospital, Tongji University School of Medicine, Shanghai, China
• ³ Department of urology Chongming Branch Of Shanghai Tenth People’s Hospital Affiliated To Tongji University, Shanghai, China
• ⁴ Department of Urology, Shanghai Tenth People's Hospital, Tongji University, Shanghai, Shanghai Municipality, China

Background: The association between body mass index (BMI) and kidney stone formation may vary across different age groups and follow nonlinear patterns.Methods: This study analyzed data from NHANES 2009-2018, including 14,880 participants aged ≥ 20 years, to evaluate the association between BMI and the risk of kidney stones. BMI was categorized as normal weight (<25.0 kg/m²), overweight (25.0-29.9 kg/m²), and obesity (≥30.0 kg/m ² ). Weighted logistic regression models were employed to adjust for multiple confounders, including sex, age, race/ethnicity, education level, smoking history, alcohol consumption, coronary heart disease, diabetes mellitus, hypertension, and physical activity. Interaction effects between BMI and key variables such as sex, race/ethnicity and other factors were also analyzed.Age-stratified analyses were performed for the groups aged 20-39 years, 40-59 years, and ≥60 years. A restricted cubic spline model was used to explore the non-linear relationship between BMI and the risk of kidney stones.Results: After adjusting for confounders, participants with a BMI ≥30 kg/m² had a significantly higher risk of kidney stones compared to those with a BMI <25 kg/m² (adjusted OR [aOR]: 1.86; 95% CI: 1.48-2.34; p < 0.001), with the association being most pronounced in the 40-59-year age group (aOR: 2.02; 95% CI: 1.36 -3.02; p < 0.001). The interaction analysis did not reveal significant interactions between BMI and sex or other factors. Non-linear analysis indicated that the relationship between BMI and kidney stone risk differed across age groups. In the 40-59-year group, the risk of kidney stones peaked and then plateaued as BMI increased beyond a certain threshold. In the ≥60-year age group, risk initially increased with BMI but then slightly declined. This non-linear relationship suggests that the impact of BMI on kidney stone risk varies by age and should be considered in clinical strategies.Conclusion: High BMI is significantly associated with an increased risk of kidney stones, particularly among middle-aged and older adults. The relationship between BMI and kidney stones is non-linear, highlighting the need to develop age-specific BMI management strategies to reduce the occurrence of kidney stones.