Calcium does not inhibit iron absorption or alter iron status in infant piglets adapted to a high calcium diet

The purpose of this study was to investigate whether a dietary calcium:iron ratio similar to that often consumed by premature human infants inhibits i ron absorption in infant piglets adapted to a high calcium diet. Male Yorks hire piglets were randomized at 3 to 4 d of age to a high calcium diet (4.6 7 g/L = HC) or a normal calcium diet (2.0 g/L = NC) and fed for 2 to 2.5 wk . An iron dextran injection was administered in amounts to achieve a margin al state of iron repletion to simulate iron status of premature infants. In vivo iron absorption from the diet was determined using the radiotracers F e-55 and Fe-59 and whole body counting. Calcium:iron interactions at absorp tion sites in piglets fed HC and NC were investigated by measurements of ti me-dependent 59Fe uptake in response to different calcium:iron ratios in vi tro in brush border membrane vesicles (BBMV), In vivo iron absorption from the diet did not differ between NC and HC diet groups [57 +/- 8% versus 55 +/- 17% (mean +/- SD), respectively]. Iron status and iron contencentration s in spleen, liver, intestine, kidney and heart did not differ between diet groups. Iron uptake in BBMV was significantly reduced by calcium in both H C and NC (P < 0.001); but there were no significant differences in iron upt ake in response to different calcium:iron ratios between HC and NC. With fe eding a HC diet for 2 wk there may be an adaptive response to counteract th e inhibitory effects of calcium on iron absorption, thus resulting in simil ar in vivo iron absorption and iron status irrespective of the 1.3-fold dif ference in dietary calcium:iron ratio between piglet groups. However, futur e studies are needed to determine the specific sites of calcium:iron intera ctions and adaptation mechanisms. Since the calcium:iron ratios used in thi s study reflect the usual calcium:iron ratios in diets for premature infant s, it is unlikely that interactive effects of calcium with iron will compro mise iron status in this infant population when diets are supplemented with calcium.