Effect of calcium supplements to a maize-soya diet on the bioavailability of minerals and trace elements and the accumulation of heavy metals in growing rats

Thirty-five (five groups with seven animals each) male albino rats (initial average weight = 44g) were fed phytate-rich diets (analysed phytic acid co ncentration = 6.9 g/kg) based on maize and soy bean meal (5 g Ca, 3 g P, 1. 2 g Mg, 23 mg Zn, 10 mg Pb, 5 mg Cd/kg diet). Experimental diets were suppl emented with 0, 2, 4, 6 and 8 g calcium from CaCO3 per kg. The supplementat ion of increasing amounts of calcium resulted in a dose-dependent decrease in the apparent absorption of phosphorus. Furthermore, apparent zinc absorp tion and femur zinc concentration were moderately decreased due to the calc ium supplementation. Kidney Cd concentration was significantly lower in rat s that were Zed the high calcium diets in comparison with the control anima ls. Femur lead concentration and hepatic 8-aminolevulinic acid dehydratase, which are known to be sensitive parameters of lead accumulation remained u nchanged by the different dietary treatments. Magnesium absorption as well as liver and plasma zinc concentration and activity of plasma alkaline phos phatase were also unaffected. Although calcium supplementation may lead to a decrease in the accumulation of certain heavy metals such as cadmium, the carry-over of lead was not affected under the given experimental condition s. Furthermore, calcium-phytate-zinc interactions may adversely affect zinc bioavailability in growing rats.