Effects of calcium carbonate and hydroxyapatite on zinc and iron retention in postmenopausal women

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Abstract
We measured the effect of calcium carbonate and hydroxyapatite on whole-body retention of zinc-65 in 11 and iron-59 in 13 healthy, postmenopausal women. In a single-blind, controlled, crossover study, each subject, on three occasions, ingested a standard test meal supplemented with iron-59 or zinc-65 and capsules containing placebo or 500 mg elemental calcium as calcium carbonate or hydroxyapatite. Whole-body countings were performed prior to, 30 min after, and 2 wk after each meal. Mean (SEM) zinc retention was 18.1 ± 1.0% with placebo (control) and did not vary significantly with calcium carbonate (110.0 ± 8.6% of control) or hydroxyapatite (106.0 ± 7.9% of control). Iron retention, 6.3 ± 2.0% with placebo, was significantly reduced with both calcium carbonate (43.3 ± 8.8% of control, p = 0.002) and hydroxyapatite (45.9 ± 10.0% of control, p = 0.003). Iron absorption may be significantly reduced when calcium supplements are taken with meals.

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