Mineral metabolism of aging female rats fed various commercially available calcium supplements or yogurt

The utilization of calcium from commercially available calcium supplements and yogurt and the effects of these calcium supplements on the utilization of other minerals were evaluated. Moderate and high levels (4 and 8 mg Ca/g diet) of calcium from four different sources of dietary calcium (yogurt, calcium phosphate dibasic, calcium magnesium chelate, and oyster shells) were fed to retired female breeder rats. Rats absorbed calcium equally efficiently from all four sources but ingestion of calcium phosphate dibasic tended to cause abnormal accumulation of calcium in kidneys. Ingestion of the calcium magnesium chelate improved calcium retention in bone but depressed the digestibility of the total diet. The elevation of dietary calcium did not affect tissue calcium levels or fecal beta-glucuronidase activity but depressed the apparent absorption of phosphorus, increased kidney phosphorus levels, decreased tibia iron levels, and decreased the digestibility of the total diet.