Effect of phytic acid, tannic acid and pectin on fasting iron bioavailability both in the presence and absence of calcium.

OBJECTIVE

To determine the effect of phytic acid, tannic acid and pectin on fasting non-heme iron bioavailability in both the presence and absence of calcium.

RESEARCH METHODS

Twenty-eight apparently healthy adult females participated in two iron absorption studies using radioactive iron isotopes ((59)Fe and (55)Fe). One group received 5mg of iron (as FeSO4) alone (control), together with 10mg of phytic acid, 100mg of tannic acid and 250mg of pectin (study A), on different days. The second group received the same iron doses and compounds as the other group, plus 800mg of calcium (CaCl2) (study B). The compounds were administered after an overnight fast, and no food or beverages were consumed for the following 3h. Iron status and circulating radioactivity were measured in venous blood samples.

RESULTS

The geometric means of iron bioavailability (range±1SD) for iron alone, iron with phytic acid, iron with tannic acid, and iron with citrus pectin were 25.0% (11.9-52.0); 18.9% (9.9-35.8); 16.8% (8.7-32.3); and 21.1% (10.2-43.9), respectively (repeated-measures ANOVA, p<0.02 (Dunnett's post hoc: control vs tannic acid p<0.05). When 800mg of calcium was added (study B), iron bioavailability was 16.7% (10.1-27.5); 13.2% (7.1-24.6); 14.8% (8.8-25.1); and 12.6% (5.5-28.8), respectively (repeated-measures ANOVA, NS).

CONCLUSIONS

Tannic acid decreases the fasting bioavailability of non-heme iron, however this effect did not exist in the presence of calcium. No effect was observed by phytic acid or citrus pectin on fasting non-heme iron bioavailability in both the presence and absence of calcium.