Influence of dietary zinc and cadmium on iron bioavailability in mice and rats: oyster versus salt sources.

Two feeding studies with young mice and one in situ intestinal perfusion study with adult rats were conducted to evaluate the influences of intrinsic (oyster) and extrinsic sources of cadmium and zinc on iron metabolism. When oyster was included in the diets, less cadmium accumulated in small intestines whether the cadmium was supplied as cadmium chloride or cadmium intrinsic to oyster. Increasing the zinc concentration of diets containing 2 ppm cadmium reduced cadmium retention in the small intestine regardless of whether the zinc supplied was intrinsic to oyster or as zinc carbonate. Dietary cadmium (20 ppm) reduced iron retention in the small intestine. Increasing dietary intrinsic zinc from 290 to 450 ppm reduced iron retention in small intestine whereas zinc carbonate did not. Inclusion of oyster in low cadmium diets reduced iron retention in the liver. Short-term in situ studies indicated salt sources of cadmium and zinc reduce uptake of iron from the intestine. Iron concentrations in the blood peaked between 20 and 55 min after exposure whether the iron was supplied alone or in combination with cadmium or zinc. The results suggest foods containing high concentrations of cadmium and zinc may reduce the availability of iron.