MEASURING THE DIETARY BIOAVAILABILITY OF CALCIUM (Ca) IN PREMATURE INFANTS WITH THE STABLE ISOTOPE ⁴⁶Ca

Abstract

The dietary bioavailability of Ca was determined on 12 occasions in 10 AGA premature infants (GA 29.9±0.3 wks, BW 1198±28 gm mean ± SEM) with stable isotope techniques. A tracer dose of ⁴⁶Ca that provided a 5 to 7-fold enrichment of dietary ⁴⁶Ca was given during one scheduled intermittent gavage feeding for each determination. Five studies were performed in 4 infants (wt 1100-1500 gm, age 15-37 days) fed a whey-predominant premature formula; 3 in 2 infants (wt 1455-1560 gm, age 26-30 days) fed their own mother's preterm milk (PTHM); and 4 in 4 infants (wt 1500-1690 gm, age 20-25 days) fed fortified-PTHM, a 1:1 (V/V) mixture of the premature formula and their own mother's milk. A 72 hr stool collection, bracketed by carmine red, was initiated with the administration of ⁴⁶Ca. The stool contents of ⁴⁶Ca and ⁴⁸Ca were determined with neutron activation analysis on each stool from 3 studies and after pooling in 9. Pooling was found to slightly underestimate ⁴⁶Ca absorption because of reentry of about 0.5% of the absorbed ⁴⁶Ca into the GI tract/24 hr. The % ⁴⁶Ca absorption was 80±4% (range 65-87%) from formula, 89±4% (85-97%) from PTHM, and 81±6% (range 69-96%) from fortified-PTHM. Thus, assuming that preterm infants handle ⁴⁶Ca like dietary Ca, about 80% of dietary Ca is bioavailable. This value is comparable to data from standard Ca balances.

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