Effects of Aging and a High-Phosphorus Diet on Bone Metabolism in Mice

The effects were investigated of aging and a high-phosphorus (P) diet on bone metabolism in mice. C57BL/6J strain mice, aged 4, 12, 24 and 80 weeks, were randomly divided into two experimental groups (C and HP), each at the same age, one group being fed with a control diet (0.5% P) and the other with a high-P diet (1.0% P) for 28 days. The results with the control diet showed the 80-week-old mice to have a higher serum parathyroid hormone (PTH) concentration than the mice at the other ages. The serum osteocalcin concentration and urinary excretion of the C-terminal telopeptide of type I collagen (CTx) were significantly lower in the 12, 24 and 80-week-old mice than in the 4-week-old mice, the urinary CTx excretion being significantly higher in the 80-week-old mice than in the 24-week-old mice. The breaking force and stiffness of the femur were both significantly higher in the 12, 24 and 80-week-old mice than in the 4-week-old mice, the stiffness of the femur being significantly lower in the 80-week-old mice than in the 24-week-old mice. The high-P diet resulted in a higher serum PTH concentration in the 12, 244 and 80-week-old mice, and a higher serum osteocalcin concentration and urinary CTx excretion in the 4, 12, 24 and 80-week-old mice than in the same-age animals fed on the control diet. The breaking force of the femur was significantly decreased by the high-P diet in the 80-week-old mice, while the stiffness of the femur was significantly decreased by the high-P diet in the 24 and 80-week-old mice. These results suggest that the high-P diet increased the bone turnover at all stages of life. Furthermore, the high-P diet seemed to have a greater effect on bone metabolism in the old mice than in the young and adult mice from the different response in PTH secretion.