Iron Absorption from the Whole Diet, Comparison of the Effect of Two Different Distributions of Daily Calcium Intake

Essay by todd bowenUniversity, Master'sB+, December 1996

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Hypothesis - If a woman distributes her daily intake of calcium by having less of it in her lunch and dinner meals and more in her breakfast and evening meals, then this would reduce the inhibitory effects calcium has on heme iron and nonheme iron absorption.

Background Information - This experiment is one of many that addresses calcium's inhibitory affects on iron absorption. In 1994, the Consensus Development Panel in Optimal Calcium Intake suggested an increase of the current Recommended Dietary Allowances of calcium(Whiting, p.77). This goal of this increase was to aid in the prevention of osteoporosis and other bone diseases. Unfortunately, this attempt at prevention could have an adverse affect on the human body's ability to absorb iron.

Recent studies have shown that eating a normal daily allowance of calcium cuts iron absorption by as much as 50-60%(Hallberg et al. p.118). Other studies examine the affect of iron bioavailability on menstruating, pre-menopausal, and post-menopausal women(Rossander-Hulten et al and Gleerup et al).

One of the fears of an increased amount of calcium intake is the increased possibility of anemia in women who are already susceptible to this condition. The iron inhibition by calcium is a classical example of how the correction of one nutritional problem can be the cause of another.

The physiological mechanism of this calcium-iron relationship remains a mystery, however there are two feasible theories. One states that calcium competes for an iron binding site on intestinal epithelial cells. It is believed calcium binds to the protein mobilferrin on the epithelial cells, which is the iron transport protein(Whiting, p.78). Another group of scientists theorizes that iron is able to be transported into the epithelial cells without problem, however the iron then has trouble getting into the blood stream. The presence of calcium inhibits iron's ability to leave...