Effect of calcium intake on nonheme-iron absorption from a complete diet

Recent studies based on radioiron measurements from single meals have suggested that calcium has a strongly inhibitory influence on nonheme-iron absorption. In view of evidence that the importance of various dietary enhancers and inhibitors of absorption is greatly diminished when assessed by labeling a complete diet, the present study evaluated the effect of variations in calcium intake on total dietary nonheme-iron absorption. Nonheme-iron absorption was measured in 14 healthy volunteers during three periods in which the diet was freely chosen or modified to decrease or increase dietary calcium intake maximally. The diet was labeled during each 5-d period by including with each of the two main meals of the day a small bread roll tagged extrinsically with radioiron. Carefully maintained dietary records indicated that 69-78% of the daily iron intake was labeled by this method. The basal calcium intake of 684 mg/d varied from 280 to 1281 mg/d when calcium intake was reduced or increased, respectively. Geometric mean iron-absorption values of 5.01%, 4.71%, and 5.83% for the three dietary periods were not significantly different from one another. No significant relation was observed between nonheme-iron absorption and dietary factors known to influence iron absorption. We conclude that calcium intake had no significant influence on nonheme-iron absorption from a varied diet.