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Published on: August 8, 2019
Body size and 24-hour urine composition.
1Renal Division and Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. entaylor@partners.org
Summary
Higher body mass index (BMI) is linked to increased urinary oxalate, uric acid, sodium, and phosphate. This may explain why obesity increases the risk of uric acid kidney stones.
Area of Science:
- Nephrology
- Urology
- Epidemiology
Background:
- Obesity, indicated by a higher body mass index (BMI), is a known risk factor for kidney stone formation.
- The precise relationship between BMI and the urinary excretion of lithogenic factors requires further clarification.
Purpose of the Study:
- To investigate the association between body mass index (BMI) and 24-hour urinary excretion of various lithogenic factors.
- To explore how BMI influences urine composition and supersaturation in relation to kidney stone risk.
Main Methods:
- Analysis of urine samples from participants in three large cohorts (Health Professionals Follow-Up Study, Nurses' Health Study, Nurses' Health Study II).
- Assessment of urine pH, volume, and excretion of calcium, oxalate, citrate, uric acid, sodium, magnesium, potassium, phosphate, and creatinine.
- Stratification of participants into BMI quintiles and application of linear regression models adjusted for relevant covariates.
Main Results:
- Higher BMI correlated with increased urinary excretion of oxalate, uric acid, sodium, and phosphate.
- An inverse relationship was observed between BMI and urine pH.
- Urinary supersaturation of uric acid increased with higher BMI, while calcium oxalate supersaturation showed no consistent relation after adjustments.
Conclusions:
- Increased urinary calcium excretion associated with higher BMI may be influenced by dietary factors like animal protein and sodium intake.
- Elevated risk of kidney stones in obese individuals may be primarily attributed to an increase in uric acid nephrolithiasis.
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