Effect of oral and intravenous calcium load on glucose-induced insulin secretion in obese children.

The effect of intravenous (IV) (10 ml of 10% calcium gluconate) and oral (3 g calcium) calcium on plasma immunoreactive insulin (IRI) and blood glucose levels was investigated during intravenous (0.5 g/kg bwt. glucose) and oral (1.75 g/kg bwt. glucose) glucose tolerance test in 21 control (body fat 14.0 +/- 0.5%) and 34 obese (body fat 36.1 +/- 0.7%) children. Calcium given before IV glucose tolerance test and IV or oral calcium by itself did not alter blood glucose and plasma IRI concentrations in either group. Oral calcium load significantly increased the glucose-induced IRI response and decreased the blood glucose levels in obese children with impaired glucose tolerance (n = 7) compared to the levels without calcium. Since IV calcium did not alter the plasma IRI concentration, it has been assumed that oral calcium exerts its effect by influencing the secretion of an insulin secretogogue gastrointestinal factor (gastric inhibitory polypeptide ?). This effect, however, was observed only in obese children with impaired glucose tolerance.