CALCIUM AND PHOSPHORUS ECONOMY OF THE PRETERM INFANT AND ITS INTERACTION WITH VITAMIN D AND ITS METABOLITES

Senterre, J. and Salle, B. (Departments of Neonatology, University hospital, Liege, Belgium and Lyon, France). Calcium and phosphorus economy of the preterm infant and its interaction with vitamin D and its metabolites. Acta Paediatr Scand, Suppl. 296: 85, 1982.—One hundred and seventeen 3-day metabolic balance studies were carried out in 69 preterm infants. Matched groups of infants were fed either banked human milk, an infant formula or a low birthweight infant formula with medium-chain triglycerides. In addition groups were constituted according to the vitamin D intake or the administration of 1,25–dihydroxyvitamin D. In infants fed human milk, mean fat absorption was 77%. Calcium absorption was 49±11% with no vitamin D supplementation and it reached 70±11% with a daily oral dose of 30 g of vitamin D. However in this latter group urinary excretion of calcium was very high because of the low phosphorus intake. With infant formula, mean fat absorption was 73%. Calcium absorption was 20±11% with no vitamin D supplementation, 32±13% with 25 g of vitamin D per day and 49±10% with daily administration of 0.5 g of 1,25-dihydroxyvitamin D. With low birthweight infant formula, mean fat absorption was 90%. Calcium absorption was 32±15% with no vitamin D supplementation, 45±13% with 25 g of vitamin D, 59±10% with 50 g of vitamin D and 58±6% with 0.5 g of 1,25-dihydroxyvitamin D per day. However with this active metabolite of vitamin D, serum level and urinary excretion of calcium were significantly higher. Whatever the milk or the vitamin D intake, phosphorus absorption was about 90%. Phosphorus retention was related to nitrogen plus calcium retentions. This study indicates that vitamin D status is the major factor regulating intestinal absorption of calcium. Activation pathways of vitamin D and gut response to 1,25-dihydroxyvitamin D are operative in preterm infant. However in populations where relative vitamin D deficiency is common as in the present study, it seems necessary to give preterm infants a daily oral dose of 30 to 50 g (1200–2000 IU) of vitamin D for achieving maximal calcium absorption. Preferably, plasma 25-hydroxyvitamin D level should guide the clinician in estimating the sufficiency of vitamin D intake.