In vitro interactions between calcium, zinc, copper and iron in milk- and soy-based infant formulas

Interactions among calcium, zinc, copper and iron in milk- and soy-based in fant formulas were assessed in order to evaluate the influence of supplemen tation with one trace element on the bioavailability of the others. The cri terion used to estimate the bioavailability is the percentage of dialysis, estimated by applying an in vitro method. Infant formulas were supplemented with CaCl2, ZnO, CuCO3. Cu(OH)(2). 2H(2)O and FeSO4. 7H(2)O at two levels (maximum (+) and minimum (-) allowed by the European Union). A factorial de sign at two levels with three factors (Zn, Cu and Fe addition) was carried out. The main effects and the second-order interactions of the studied fact ors on the bioavailability of a given element were estimated. The results o btained for milk-based formulas clearly indicated the negative influence of iron at the high addition level (+) on the dialysis percentage of calcium, and of zinc at the high addition level (+) on its own dialysis percentage, whereas in the same type of formulas, the addition of zinc had a positive effect on the copper dialysis percentage. Tn soy-based formulas a negative effect of added copper (+) on its own dialysis percentage was observed. The most important second order interaction found to be significant was the ne gative effect of (zinc x iron) on copper dialysis in milk-based formulas.