Calcium and phosphorus homeostasis in very-low-birth-weight infants appropriate for gestational age fed human milk.

The concentrations of calcium and phosphorus and the activity of alkaline phosphatase in serum were evaluated in 42 very-low-birth-weight (VLBW) and 83 low-birth-weight (LBW) infants on the 7th, 21st, and 42nd day of life. 9 VLBW and 16 LBW infants were randomized for measurement of the renal excretion of calcium and phosphorus on the 3rd, 5th, 7th, 21st, and 42nd day of life during human milk feeding and 14 VLBW-infants fed human milk supplemented with 1 mmol NaH2PO4 per 100 ml. All serum parameters were found to be normal. Supplementation of human milk with NaH2PO4 leads to a tendency of higher concentrations of phosphorus than found in VLBW-infants exclusively fed with native human milk, but all differences between the two groups were not significant. VLBW-infants appeared more than LBW-infants to be conserving phosphorus and wasting calcium during human milk feeding. Supplementation of human milk with NaH2PO4 results in higher phosphorus lower calcium excretion in urine of VLBW-infants, but they do not reach the values of LBW-infants. Because the activity of alkaline phosphatase was not different between the feeding groups and in all cases within the normal range a delayed bone mineralisation cannot be assumed in the infants studied. Thus, the phosphorus deficiency which is shown by the renal excretion of calcium and phosphorus in the VLBW-infants can be considered to be latent. In the light of our data the concentration of phosphorus in human milk seems to be too low and the calcium/phosphorus ratio too high for the optimal mineral metabolism in VLBW-infants. The supplementation used improves the situation, but the phosphorus intake seems still too low. Further investigations are needed to detect the optimal phosphorus intake for these infants. The calcium/phosphorus ratio in the urine is a good marker to estimate a latent phosphorus deficiency in VLBW-infants.