Bioavailability of milk calcium prepared from rennet casein in rats

An investigation was conducted on the bioavailability of milk calcium prepared from rennet casein (milk Ca preparation), in comparison with soluble calcium mixed at the same ratio as that found in milk (calcium from Ca3 (C6H5O7) 2·4H2O, 56%; CaCl2, 30%; Ca3 (PO4) 2, 14%: soluble Ca preparation), and CaHPO4. Eight-week-old SD rats were randomly divided into three groups and given the milk Ca preparation, soluble Ca preparation, or CaHPO4. All the rats received the same amount of calcium (0.52%), phosphate (0.40%), and magnesium (0.05%). Calcium balance, plasma calcitonin level, and femur calcium gain (difference in femur calcium content between 14-week-old and 8-week-old rats) in each group were determined. No significant differences in serum calcium levels, food efficiency, or body weight gain were found among the three groups. However, the milk Ca group showed significantly higher levels of urinary calcium excretion and plasma calcitonin concentration than the CaHPO4 group. In the milk Ca group, femur calcium gain was larger than that in the other two groups. These results imply that the milk Ca preparation is absorbed well and increases bone calcium content efficiently, in comparison with the soluble Ca preparation and CaHPO4.