#2980 Association between body mass index and nephrolithiasis markers in the Mexican population

Abstract Background and Aims Kidney Stone Disease is a common condition with a prevalence ranging from 10% to 15% in the population of industrialized countries in the Americas. The incidence of nephrolithiasis has been directly associated with factors such as metabolic syndrome and a Western lifestyle, characterized by the consumption of ultra-processed foods and low physical activity. In this context, body mass index (BMI) has been identified as a potential risk factor for Kidney Stone formation due to its role in metabolic alterations that affect urinary composition. This study aimed to analyze the association between BMI and nephrolithiasis markers such as pH, oxaluria and calciuria in Mexican patients diagnosed with kidney stones. Method This retrospective study included a sample of Mexican participants diagnosed with nephrolithiasis between the years 2013–2014, from whom a review of medical records was conducted. BMI was calculated based on patients’ height and weight, while nephrolithiasis markers were assessed through a 24-hour urine sample. Pearson correlation and multivariate regression analyses were performed to examine the association between BMI and nephrolithiasis markers, adjusting for potential confounding variables such as sex and age. Results A total of 585 patients with nephrolithiasis were included, of whom 59.1% were women. The mean age and BMI of the population were 53.2 ± 13.5 years and 27.9 ± 5.04 kg/m², respectively. The urinary profile of the patients was within normal parameters: pH 6.0 ± 0.9, calcium 161.4 ± 98.8 mg/day, sodium 158.6 ± 70.4 mEq/day, potassium 59.6 ± 36.9 mEq/day, phosphorus 650.7 ± 319 mg/day, oxalates 28.0 ± 18.2 mg/day, and citrates 407.9 ± 248.9 mg/day. Significant correlations were found between body weight and the following urinary parameters: pH (r = −1.88, P = 0.0001), calcium (r = 0.188, P = 0.0001), sodium (r = 0.34, P = 0.0001), oxalates (r = 0.282, P = 0.001), and phosphorus (r = 0.308, P = 0.0001). BMI showed significant correlations with fewer urinary parameters: pH (r = −1.51, P = 0.0001), sodium (r = 0.24, P = 0.0001), oxalates (r = 0.203, P = 0.023), and phosphorus (r = 0.144, P = 0.001). In the linear regression analysis, BMI was not a strong predictor of urinary parameters. However, body weight was found to be a significant predictor of urinary pH, calcium, sodium, potassium, phosphate, and citrates (Table 1). For each kilogram of body weight, urinary pH decreased by 0.11, while urinary calcium increased by 2.15 mg. Despite being a predictor of urinary parameters, the β values were low, and the R² of the models explained only a small proportion of the variability in the patients' urinary profiles. These findings suggest that weight gain in patients with nephrolithiasis may alter urinary composition, increasing the risk of crystallization and the formation of new kidney stones. Conclusion This study reveals that BMI is not a predictor of the urinary profile in patients with nephrolithiasis. Body weight was identified as a predictor of urinary pH, calcium, sodium, potassium, phosphate, and citrates. Although body weight explains only a small proportion of the variations in these parameters, maintaining an adequate body weight in patients with nephrolithiasis is essential to reduce the risk of recurrent kidney stone formation.