Bioavailability of Different Iron Compounds Used to Fortify Formulas and Cereals: Technological Problems

Bioavailability of a single iron source is difficult to predict. It can vary considerably due to the enhancing or inhibitory effects of other food components on iron absorption and, especially for the less-available sources, it is strongly influenced by the physical characteristics of the iron compound itself. It is sometimes difficult for the food manufacturer or food scientist to interpret the many apparent contradictions in the literature, further complicated by the different methodologies used by different research groups and the difficulties in extrapolating from rats to humans. Table 1 shows an advisory list of iron sources that may be used in foods for infants and young children (1). It includes the most frequent uses of these salts and an estimate of their relative bioavailability when compared to ferrous sulphate in both rats and humans. In rat studies, iron compounds have been compared to ferrous sulphate by evaluating the regeneration of hemoglobin in iron-depleted rats. In human studies, differences in iron absorption in iron-replete healthy men have been measured using radioactive isotopes. It should be remembered that the studies of Brise and Hallberg (6), which were used to calculate most of the reported values, were made by giving fasting subjects iron sources containing 30 mg elemental iron. The relative properties of different iron compounds may change when given with food. Nevertheless, it is readily noticeable from the information available that both rat and human assays give the same ranking to the bioavailability of the different salts and that, in general, iron sources added to infant formulas are more highly available than those commonly added to infant cereals.