Effect of Phosphate Supplementation to Breast Fed Very Low Birthweight Infants on Urinary Calcium Excretion, Serum Immunoreactive Parathyroid Hormon and Plasma 1.25-Dihydroxy-vitamin D Concentration

. The effect of two doses of Phosphorus (P) supplementation to pooled breast milk (BM): 0.48 and 0.800 mmol/kg/24 h given during the second month of life was evaluated in 22 very low birthweight infants. The concentration of calcium and phosphorus in serum and urine, the serum concentration of immunoreactive parathyroid hormon (iPTH) and the plasma 1,25-dihydroxy-vitamin D concentration (1,25-OH-D) were compared to the values in 19 control infants. The mean ± SD concentrations in control infants and adults are 63 ±18 ulEq/ml for serum iPTH and 85±pmol/l for plasma 1,25-OH-D. With 0.48 P supplementation, urinary Ca (UCa) excretion (median and range) 0.238 mmol/kg/24 h (0.105-0.520) was lower than in the control group 0.288 (0.205-0.679) (p<0.05); the reduction of UCa was larger with 0.8 P supplementation: 0.047 (0.023-0.163) (p<0.01). P supplementation induced no change in serum Ca concentration but a slight and significant increase in serum iPTH was observed only with the 0.8 P supplementation: 55 μl Eq/ml (<25-80) (p<0.05). With 0.8 P supplementation there was no significant change of plasma 1,25-OH-D concentration: 173 μmol/l (106-271) vs. 255 (132-293) in the control group. These data show that with 0.8 P supplementation, the hypercalciuria in BM-fed infant disappears without secondary hyperparathyroidism, but without any change in plasma 1,25-OH-D concentration.