Does the response of bone mass to calcium supplements depend on calcium absorption efficiency?

Abstract

OBJECTIVE: Calcium supplements can reduce bone resorption and slow bone loss after the menopause, but these effects may be limited by poor intestinal absorption. Since the increase in blood ionised calcium and decrease in serum parathyroid hormone after a calcium load are diminished in patients with poor calcium absorption, we aimed to see whether the response of bone mineral content (BMC) to calcium is related to initial calcium absorption. DESIGN: We retrospectively examined the changes in forearm BMC in 164 patients (139 women and 25 men) receiving calcium therapy alone for low bone density in a university hospital. METHODS:BMC was measured in a Molsgaard single energy absorptiometer and calcium absorption in a single blood sample 1 h after a dose of 5 muCi (45)Ca in 20 mg calcium carrier. Results were analysed by simple and multiple regression analysis. RESULTS: Mean forearm BMC did not change significantly over the mean 43 (s.D., 33) months of treatment (1.023 (0.247) to 1.017 (0.246) g/cm). The annual percentage of change was positively related to both body weight (r=0.180; P=0.020) and radiocalcium absorption (r=0.185; P=0.017). Multiple linear regression confirmed that both variables contributed to the change in BMC (P=0.023 and 0.019 respectively). The mean annual percentage of change in BMC on calcium therapy was not related to age, initial BMC, serum 1,25-dihydroxyvitamin D or fasting urinary calcium/creatinine ratio. CONCLUSIONS: These results support our earlier studies which suggest that poor calcium absorption limits the response of bone to calcium supplements.