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

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 ¼ 117) and elderly (55-75years; n ¼ 85) having a mean body mass index (BMI) of 22.8073.4 and 25.373.9 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 (Po0.05) 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, Po0.0001), followed by urea (Po0.0001), creatinine (Po0.05), and BMI (Po0.05 for the young adults and P ¼ 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.

Influence of lean and fat mass on bone mineral density and on urinary stone risk factors in healthy women

“…On the other hand, if we consider urinary factors of lithogenic risk, an inverse correlation between pH and BMI and between pH and fat mass has been reported [7]. Moreover, the excretion of oxalate has been linked to body weight, body surface area and to lean mass [8].…”

Acid Base Considerations in Stone-Age Farming Sweet Potato Eaters, Modern-Day Sweet Potato Eaters, and High-Protein Consumers

“…In recent papers, we studied total OA excretion rates in children and adolescents [3] as well as associations between anthropometry and acid-base parameters in young adults and elderly [18]. Based on the available OA measurements in adolescents [3] and complementary OA analyses in a group of elderly [18], we additionally examined whether higher protein intakes may have significant associations with urinary total OA excretion rates.…”

“…Based on the available OA measurements in adolescents [3] and complementary OA analyses in a group of elderly [18], we additionally examined whether higher protein intakes may have significant associations with urinary total OA excretion rates. In all subjects, protein intake was estimated from urinary total nitrogen excretion after allowing for potential correlated measurement errors as described elsewhere [19].…”

Nutritional psychiatry research: an emerging discipline and its intersection with global urbanization, environmental challenges and the evolutionary mismatch

“…Notwithstanding the pseudoscientific extrapolation of the low-grade acidosis proposal into so-called alkaline diets by lay writers, intriguing prospective research has shown that dietary acid load increases subsequent risk of type 2 diabetes [244]. Acid load has also been linked to cardiovascular health [245], elevated body weight, increased waist circumference and a lower percentage of lean body mass [246-248]. …”