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Am J Clin Nutr. 2019 May 1;109(5):1279-1287. doi: 10.1093/ajcn/nqy379.

Increased body fatness adversely relates to 24-hour urine pH during childhood and adolescence: evidence of an adipo-renal axis.

Author information

1
DONALD Study Center, Department of Nutritional Epidemiology, Institute of Nutrition and Food Science, University of Bonn, Dortmund, Germany.

Abstract

BACKGROUND:

Reduced net acid excretion (NAE) capacity indicates a decrease in renal function. This reduction manifests as a disproportionally low 24-h urine pH in relation to the sum of actually excreted ammonium and titratable acidity by the kidney.

OBJECTIVE:

The aim of this study was to test the hypothesis that higher body fatness is one determinant of kidney function impairment with a lowered urine pH even at a young age.

METHODS:

NAE, pH, urea, and creatinine were measured in 24-h urine samples from 524 healthy children and adolescents (aged 6-17 y) participating in the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) Study. Body fatness was assessed anthropometrically by body mass index-standard deviation score (BMI-SDS), fat mass index (FMI), body fat % (BF%), and waist circumference (WC). Multivariable linear and mixed linear regressions were used to examine cross-sectionally (n = 524 urine samples; age groups: 6-8, 9-11, 12-14, 15-17 y) and longitudinally (n = 1999 urine samples) the associations of body fatness with 24-h urine pH as the outcome variable, respectively.

RESULTS:

After adjusting for the kidneys' total net acid load (24-h urinary NAE) and further relevant covariates, FMI showed significant inverse relations with urinary pH in all 4 age groups, and BMI-SDS, BF%, and WC each in 3 out of these 4 groups (P ≤ 0.02). Longitudinal results substantiated these interindividual relations and further showed intraindividual increases in body fatness to be paralleled by urine pH decreases (P ≤ 0.0002).

CONCLUSIONS:

Independent of underlying acid load, an early increase in body fatness is associated with increased free proton excretion, and thus with a decline in the kidney's acid excretion function, which could potentiate the risk of renal nephrolithiasis.

KEYWORDS:

24-h urine pH; adipo-renal axis; body fatness; healthy children; kidney function; renal net acid excretion

PMID:
30997510
DOI:
10.1093/ajcn/nqy379

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