Mineral metabolism in obese children

Blood levels of glucose, insulin (IRI), Calcium (Ca), phosphorus (P), alkaline phosphatase (AP), osteocalcin (OC), parathyroid hormone (PTH), calcitonin (CT), 25-hydroxyvitamin D3 (25OHD3), 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and urinary excretion of Ca (Ca/Cr), P (TmP/GFR), hydroxyproline (OH-P/Cr) and cyclic AMP (cAMP/GFR) were determined in 16 obese children, aged 8 to 11 years, on a diet rich in calories and carbohydrates and in 15 controls of the same age. Blood glucose, IRI, Ca, P, PTH and CT were also determined in both groups of subjects, during an oral glucose tolerance test (OGTT). In basal conditions glucose, IRI, AP, OC, PTH, CT and 1,25(OH)2D3 levels were significantly higher, and 25OHD3 levels lower, in obese children than in controls. Urinary Ca/Cr, TmP/GFR were lower in obese than in non obese children, while OH-P/Cr and cAMP/GFR were higher. Bone mineral content (BMC), measured by photon absorptiometry, and BMC/bone width ratio were lower in obese than in non obese children. During OGTT serum Ca and P decreased and serum PTH and CT increased less in obese than in non obese children. In obese children receiving a diet with high carbohydrate content, an alteration of mineral metabolism occurred, characterized by secondary increase of PTH and 1,25(OH)2D3. Ca decreased and PTH and CT increased less markedly during OGTT.