Recommended dietary intakes of iron, zinc, and other inorganic nutrients and their chemical form and bioavailability.

The bioavailability of a nutrient can, in some cases, be significantly influenced by the chemical form in which it appears in the diet and by the presence of other factors in food that may enhance or depress mineral absorption and utilization. With inorganic nutrients in particular, it is important to understand the physicochemical factors that underlie the differences in bioavailability of some trace elements from diets of differing composition, so that meaningful recommended dietary intakes (RDIs) may be set for these nutrients in relation to the dietary profiles of the countries in which they are to be used. Iron and zinc are especially noteworthy in this regard because their absorption can be greatly influenced by chemical form, ionic competition for uptake mechanisms, and the presence of favorable or unfavorable chelating and binding agents in the diet. Recognizing this variability, several national and international authorities recommending RDIs for these nutrients list a range of desirable intakes that relate to the estimated bioavailability of the mineral from various dietary regimens.