Effect of childhood obesity and obesity-related cardiovascular risk factors on glomerular and tubular protein excretion

Abstract

There is increasing evidence that obesity may damage the kidney in otherwise healthy individuals. Our study investigated the effect of childhood obesity on urinary albumin and beta-2-microglobulin excretion, and the association of these with obesity-related cardiovascular risk factors. Random morning spot urine samples were collected from clinically healthy obese (n = 86; median age 12.9 years, range 8.9-17.2 years; median weight 80.6 kg, range 46.1-136.8 kg; median body mass index 30.4 kg/m2, range 24.5-43.2 kg/m2) and normal weight children (n = 79; median age 13.5 years, range 10.7-14.9 years; median weight 51.0 kg, range 27.3-72.5 kg; median body mass index 18.2 kg/m2, range 13.2-23.9 kg/m2). The obese children were examined for the presence of common obesity-related cardiovascular risk factors including hyperinsulinaemia, impaired glucose tolerance (IGT), dyslipidaemia, hypercholesterolaemia, and hypertension. Obese children had a significantly higher urinary albumin/creatinine ratio (U-ACR) (median 11.7 mg/g, interquartile range 12.9 mg/g versus median 9.0 mg/g, interquartile range 5.1 mg/g; P = 0.003) and urinary beta-2-microglobulin/creatinine ratio (U-BMCR) (median 63.9 microg/g, interquartile range 34.7 microg/g versus median 34.6 microg/g, interquartile range 44.1 microg/g; P < 0.001) than normal weight children. Among the obese children, the U-ACR was associated with fasting hyperinsulinaemia, IGT, and hypercholesterolaemia (all P < 0.05), and significantly correlated with the fasting (r = 0.23, P < 0.05) and 2-h (r = 0.37, P < 0.001) plasma glucose levels measured during an oral glucose tolerance test. Obese children with no more than one of the features of the metabolic syndrome had significantly lower U-ACRs than obese children with two or more features (median 10.4 mg/g, interquartile range 5.8 mg/g versus median 15.3 mg/g, interquartile range 14.9 mg/g; P < 0.05). According to our results, clinically healthy obese children have a higher degree of albuminuria and beta-2-microglobulinuria than normal weight children, indicating early renal glomerular and tubular dysfunction as a consequence of childhood obesity. The urinary albumin/creatinine ratio in the obese children was associated with certain metabolic derangements linked to obesity, and also with the clustering of features of the metabolic syndrome.