Effects of different calcium sources on iron absorption in postmenopausal women

We measured the effect of calcium from food and supplement sources on whole-body retention of 59Fe in 19 normal postmenopausal women. Each woman received a placebo and 500 mg calcium from a mixed calcium citrate-malate salt (CCM), from orange juice plus CCM, and from milk after a test breakfast meal to which 59Fe had been added. The test meal contained 238 mg calcium. Whole-body countings of 59Fe were performed before and 30 min and 2 wk after each test meal. Retention of 59Fe was 8.3 +/- 1.1% (means +/- SEM) with placebo, 3.4 +/- 0.78% with milk, 6.0 +/- 0.97% with CCM, and 7.4 +/- 1.7% with CCM plus orange juice. When compared with placebo, milk and CCM significantly lowered iron retention (p less than 0.05) whereas CCM plus orange juice did not. The reduction with milk was greater than that with CCM (p less than 0.05) or CCM plus orange juice (p less than 0.05). The differences in the effects of these calcium sources on 59Fe retention may result from their varied contents of citric and ascorbic acids, known enhancers of iron absorption.