Muscularity and adiposity in addition to net acid excretion as predictors of 24-h urinary pH in young adults and elderly

作者：Remer T^*; Berkemeyer S; Rylander R; Vormann J

来源：European Journal of Clinical Nutrition, 2007, 61(5): 605-609.

DOI：10.1038/sj.ejcn.1602560

• urinary pH
• acid-base
• NAE
• 24-h urine
• adiposity
• muscularity

Objective: In patients with nephrolithiasis, an inverse relationship between 24-h urinary pH (24h-UpH) and body weight has been reported. Whether body composition indices and 24h-UpH are similarly associated in healthy subjects needs investigation. Design: Cross-sectional, retrospective analysis. Setting: Dortmund, Germany and Gothenburg, Sweden. Subjects: Healthy young adults (18 - 23 years; n = 117) and elderly (55 - 75years; n = 85) having a mean body mass index (BMI) of 22.80 +/- 3.4 and 25.3 +/- 3.9 kg/m(2), respectively. Methods: Anthropometric data, 24h-UpH, and 24-h urinary excretion rates of net acid (NAE), creatinine, and urea were determined. After adjusting for urea (reflecting protein intake), renal creatinine output was used as a biochemical marker for muscularity. The BMI served as a marker of adiposity. Results: NAE, body weight, and BMI were significantly (P < 0.05) higher, and height and creatinine significantly lower in the elderly, whereas body-surface area (BSA) was not different. Step-wise multiple regression analysis using BSA-corrected urinary variables revealed NAE as the primary predictor of 24h-UpH (with R-2 values of 0.64 and 0.68 in young adults and elderly, respectively, P < 0.0001), followed by urea (P < 0.0001), creatinine (P < 0.05), and BMI (P < 0.05 for the young adults and P = 0.12 for the elderly). These associations were negative for NAE and BMI, and positive for urea and creatinine. Conclusions: Muscularity (i. e. creatinine adjusted for urea) and particularly in the group of young adults, adiposity (i. e. BMI) proved to be modest, but significant predictors of 24h-UpH. Future research should focus on more obese subjects in whom insulin resistance and particular kidney functions should also be examined to further substantiate the role of obesity in low-urine pH-associated conditions, for example, nephrolithiasis.

• 出版日期2007-5