682 PROSPECTIVE HIGH VS LOW CALCIUM AND PHOSPHORUS WITH FIXED LOW VITAMIN D CONTENT IN PARENTERAL NUTRITION (PN) IN INFANCY

Abstract

Vit D 50 to 1000 IU/d in PN has been suggested for infants but prospective studies are lacking. Effects of high or low Ca and P on Ca metabolism have not been examined. We hypothesized that high Ca and P with low vit D in PN results in normal Ca, P and vit D metabolism in infants. 12 wt appropriate for gestation infants (3M,9F; 11W,1B); 32-41 wks; 1780-3630g at birth with surgical indications for PN received fixed ‘low’ 25 IU vit D2/dl and were randomized to either high Ca 60mg and P 46.5mg/dl, or low Ca 20mg and P 15.5mg/dl content. Measures were made at start, 10d, 3wks and 6wks. There were no differences in serum Ca, Mg, P, alkaline phosphatase, parathyroid hormone, calcitonin, and values were normal. Mean serum 25 hydroxyvit D (25OHD, protein binding) was 16-39 for high and 15-31ng/ml for low Ca,P grp. Mean serum 1,25 dihydroxyvitamin D (1,25(OH)2D, HPLC--binding) and tubular reabsorption P (TRP) in high Ca,P grp were stable 72-47pg/ml, and, 88-80% resp; values in low Ca,P grp were higher 78-127pg/ml and 75-99% (p<0.05 covariance, high v low). Urine Ca and Mg/Creatinine were not different between grps. 5 infants on PN for 71-175d with same vit and low Ca,P had normal 250HD with high TRP and 1,25(OH)2D. Thus, PN with 1) low 25IU vit D/dl maintains normal serum 25OHD for up to 6mos 2) high Ca,P similar to that absorbed from human milk results in stable serum 1,25(OH)2D and TRP. We speculate that low Ca, P intake results in adaptive increase in 1,25(OH)2D and TRP reflecting insufficient Ca and P intake; and high Ca and P my benefit bone mineralization in long term PN.