Original Article

European Journal of Clinical Nutrition (2007) 61, 605–609. doi:10.1038/sj.ejcn.1602560; published online 22 November 2006

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

Contributions: TR and SB were basically involved in the development of study design, did basic interpretation of results, and prepared the manuscript. SB was responsible for the analysis of the urine samples to a great extent. JV and RR initiated the study and coordinated parts of the assembly of data and analysis. All authors contributed to the preparation of the manuscript.

T Remer1, S Berkemeyer1, R Rylander2 and J Vormann3

  1. 1Research Institute of Child Nutrition, Dortmund, Germany
  2. 2Biofact Environmental Health Research Center, Lerum, Sweden
  3. 3Institute for Prevention and Nutrition, Ismaning/Munich, Germany

Correspondence: Professor T Remer, Department of Nutrition and Health, Research Institute of Child Nutrition, Heinstueck 11, Dortmund D-44225, Germany. E-mail: remer@fke-do.de

Received 31 January 2006; Revised 9 August 2006; Accepted 12 September 2006; Published online 22 November 2006.

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Abstract

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 22.80plusminus3.4 and 25.3plusminus3.9 kg/m2, 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.

Keywords:

urinary pH, acid–base, NAE, 24-h urine, adiposity, muscularity

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