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).
Conclusion: 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.