Calcium supplementation has been shown to decrease bone loss by as much as 50% at nonvertebral sites. The effects are greatest in women whose baseline calcium intake is low, in older women, and in women with osteoporosis. Generally, it is recommended that women take 1000-2000 mg of calcium/ day. But which calcium is best?
Calcium salts differ in their content. Calcium carbonate contains 40% of calcium in elemental forms; calcium citrate, 24%; calcium phosphate 39%; calcium lactate, 13% and calcium gluconate, 9%. Data has been cited that shows calcium citrate is more bioavailable than calcium carbonate and may be more beneficial at the bone level. However it appears that the study was done in individuals who were fasting. In that environment, calcium citrate will be better absorbed due to the HCl production by the stomach during food digestion. When both calcium salts are taken with meals, there appears to be no difference between carbonate and citrate absorption.
However, as we age the production of HCl diminishes, and therefore calcium citrate may be a more appropriate form of supplementation.