Calcium supplements increase bone mineral density in women with low serum calcium levels during long-term estrogen therapy.

In order to clarify whether the long-term effect of estrogen on bone mineral density (BMD) is reinforced by low dose calcium supplements, 600-800 mg of calcium lactate was administered to postmenopausal or oophorectomized women who had been undergoing unopposed estrogen therapy for at least 2 years and whose serum calcium level was suppressed to below the normal range. To patients whose serum calcium levels had been within the normal range, the same dose of estrogen alone was continued. Changes in lumbar spine BMD before and after calcium supplementation was measured by dual-energy X-ray absorptiometry. Lumbar spine BMD decreased by -0.37% for 2 years in women treated with estrogen alone, while that of women treated with estrogen and calcium increased by 2.78% (P = 0.003). These results indicate that low dose calcium supplements potentiate the effect of estrogen in women with decreased serum calcium during long-term hormone replacement therapy.