Relative bioavailability of calcium-rich dietary sources in the elderly

Background: The recent increase in the dietary calcium recommendation from 800 to 1200 mg/d for persons aged > 51 y has made it important to identify alternative high-calcium dietary sources that the elderly can use in meeting their calcium requirement. Objective: We determined the bioavailability of calcium from 3 different sources: orange juice fortified with calcium-citrate malate, skim milk, and a calcium carbonate supplement. Design: Twelve subjects [9 women and 3 men with a mean (+/-SEM) age of 70 +/- 3 and 76 +/- 6 y, respectively] consumed low-calcium (300 mg/d) and high-calcium (1300 mg/d) diets for three 1-wk periods each during a 6-wk crossover study. The acute biochemical response to calcium from each of the 3 sources was assessed during a 4-h period after the initial breakfast meal of the high-calcium diet. Results: Postprandial suppression of serum parathyroid hormone did not differ significantly between the test meals containing calcium-fortified orange juice, the calcium carbonate supplement, and milk. This finding suggests that the calcium bioavailability from the 3 sources was equivalent. During the 1-wk high-calcium diet periods, fasting serum calcium increased by 3% (P < 0.0001), serum 1,25-dihydroxyvitamin D decreased by 20% (P < 0.0001), and a biomarker of bone resorption (serum N-telopeptide collagen crosslinks) decreased by 14% (P < 0.02) compared with the low-calcium diet period. However, no differences among the supplemental calcium sources were found in these calcium-responsive measures or fasting serum parathyroid hormone concentration. Conclusions: In elderly subjects, the calcium bioavailability of the 3 high-calcium dietary sources tested was equivalent, during both the acute postprandial and longer-term periods.