Calcium supplementation of mothers' mil for low birthweight infants: Problems related to absorption and excretion

Human milk is thought to be limited in calcium, phosphorous, sodium and possibly other minerals relative to estimated requirements for growing low birthweight infants. This study examined the efficacy of early supplementation of premature infants' mothers' milk (PTM) with calcium lactate (58 to 70 mg calcium/kg/24 hr) with respect to absorption of calcium, phosphorous, magnesium and dietary lipid and renal handling of major cations. Seventy-two hour metabolic balances were carried out in the first, second and fourth postnatal weeks in 14 infants born at 29.8±0.3 (mean±SEM) wk and 1286±35 g birthweight. Feeding of PTM with or without calcium supplementation (as calcium lactate) was associated with hypercalciuria in 83% of the infants studied. Supplementation with calcium resulted in greater calcium absorption but also greater urinary losses. Fecal lipid losses also increased with calcium supplementation. Absorption and excretion of phosphorous and magnesium did not appear to be altered by administration of calcium lactate. Supplementation of calcium as calcium lactate cannot be recommended for human milk fed infants. The hypercalciuria which occurred may place the developing kidney at risk of nephrocalcinosis, although this may be ameliorated by providing concurrent phosphorous therapy and conservative dietary sodium intakes. The amount and form(s) of calcium salt which can be maximally absorbed and retained with minimal interference with absorption of dietary lipid and/or other macro and trace elements from human milk has yet to be delineated.