Does calcium potentiate the bone-preserving effect of oestrogen treatment in early post-menopausal women by a change in vitamin D metabolism?

The effect of combined oestrogen/progestogen and calcium therapy on vitamin D metabolites was studied in a double-blind, controlled clinical study over a period of 12 mth. Seventeen healthy post-menopausal women were randomly allocated for treatment with either oestrogen/progestogen or placebo. All the participants received a daily calcium supplement of 0.5 g throughout the study. The oestrogen-treated group showed the well-known changes in calcium metabolic variables, i.e. decreases in serum phosphate (P less than 0.001), serum alkaline phosphatase (P less than 0.001) and 24-h urinary calcium excretion rate (P less than 0.01). However, the serum calcium and serum 1,25-dihydroxycholecalciferol concentrations were unchanged. In the placebo group all the measured values remained virtually unchanged throughout the study. The findings indicate that calcium seems to potentiate the bone-preserving effect of oestrogen treatment in early post-menopausal women by keeping the serum calcium level unchanged and thus maintaining an unchanged vitamin D metabolism.