Histomorphometric effects of calcium or calcium plus 25‐hydroxyvitamin D₃ therapy in senile osteoporosis

To evaluate the effects of calcium and 25‐OHD in the therapy of senile osteoporosis, we studied a group of 39 women aged 69 + 7 (standard deviation, SD) years with severe osteoporosis. The group was characterized histomorphometrically by depressed bone remodeling rates without hyperosteoidosis. No subject had risk factors for osteopenia other than their age and postmenopausal status, and no subject was receiving therapy for bone disease at the onset of the study. Subjects were followed for 2 years after randomization to receive either 1200 mg/day of calcium (as calcium carbonate) and 40 μg/day of 25‐OHD (calcium‐25‐OHD group), or 1200 mg/day of calcium plus placebo (calcium‐placebo group). Calcium‐25‐OHD resulted in a clear increase in 25‐OHD levels (p < 0.001) and an increase in calcium absorption as indicated by urinary calcium excretion. Nevertheless, there was no significant change in fasting serum calcium, phosphorus, alkaline phosphatase, PTH, or 1,25‐(OH)₂D in either group. Radial and phalangeal bone mineral content and trabecular bone volume in the biopsied patients remained stable in both groups over the 2 year period. Unexpectedly, repeat bone biopsies revealed a clear improvement in the rate of mineralization in both groups, presumably as a result of the calcium supplementation alone. In summary, calcium‐placebo and calcium‐25‐OHD treatment were both associated with stable appendicular bone mineral content in women with senile osteopenia. The finding of an effect of calcium supplementation on the rate of mineralization indicates that relative calcium deficiency may impair the mineralization phase of remodeling. Calcium therapy may thus provide some benefit in the therapy of osteoporosis characterized by prolonged remodeling rates.