Calcium metabolism in postmenopausal and osteoporotic women consuming two levels of dietary protein.

Eight postmenopausal women, four with osteoporosis diagnosed by their physician and four without, participated in a metabolic study to investigate the effects of level of protein intake on calcium metabolism; renal acid excretion; plasma total and ultrafiltrable calcium; 1,25-dihydroxyvitamin D; and serum immunoreactive parathyroid hormone. Radial bone mineral content was evaluated. Protein intake was 50 g/day during the 1st 15-day experimental period and 110 g during the 2nd period. Calcium, magnesium, and phosphorus intakes were held constant at 713, 323, and 1078 mg/day. The increase in protein intake significantly increased net calcium absorption and urinary calcium. A calcium intake of 713 mg was not sufficient for calcium balance for most of the women studied. The calciuretic effect of increased protein intake was associated with increased renal acid excretion. None of the plasma and serum measurements mentioned above was significantly affected by the level of protein intake except for a slight increase in plasma total calcium. No significant differences in radial bone mineral content or in any of the other measurements were observed between the osteoporotic and the normal group of women.