Reduced serum calcium and inorganic phosphate levels in normal elderly women.

Because published data on the effect of normal aging on serum calcium and phosphate levels are scanty and contradictory, we measured these parameters in 36 normal women over the age of 65 and compared these values with those obtained previously and concurrently in younger women. We found a significant decline in both serum calcium and phosphate levels after the age of 65. We also measured corrected total serum calcium, serum ultrafiltrable calcium, and serum ionized calcium levels in all of the elderly women and in 29 of the younger women and concluded that the decline in total serum calcium levels seen with aging was attributable in part to decreased levels of protein bound calcium but that there was also a slight reduction of ionic calcium levels. Data obtained in elderly women with proven parathyroid adenomas are included to illustrate how the recognition of these age related changes in total serum calcium levels may aid in the identification of slight but clinically important hypercalcemia in elderly adults.