An average adult in the U.S. on a 2,500 calorie diet ( 6 mg of iron/1,000 kcal) ingests 15 mg of iron daily. Only 5-10 % or about 1.0 mg of dietary iron is absorbed as ferrous iron (Fe++), mainly in the duodenum and upper jejunum where the pH is low. The mucosal cells oxidize the ferrous iron to ferric iron , which is then complexed with apoferritin to form ferritin. Some of the ferritin is transported out of the mucosal cell into the plasma bound to transferrin. Thus bound, iron can be transported to the bone marrow or iron storage sites where it is stored as either ferritin or hemosiderin.
Iron bioavailability is currently defined as the proportion of iron ingested that is absorbed by the intestine and used through normal metabolic pathways or stored. It is expressed as a percentage of intake and is known to be influenced by dietary and host factors (Aggett, 2010)
The pathway for intestinal haem absorption is independent from those of non-haem iron, and haem iron is almost unaffected by interactions with other food components. However, the haem form only constitutes about 10–15% of total dietary iron, thus non-haem is the main iron source.
First of all, the amount of iron ingested is a prerequisite for having bioavailable iron.
The concept of bioavailability as the “proportion” of the iron ingested that is utilized or stored for body functions has to take into account the amount of iron ingested, the meal composition and the time between meals. Haem iron is almost unaffected by interactions with other food components.
-Ascorbic acid (AA) is recognized as the most powerful iron enhancer. AA acts by forming a chelate with iron at the low pH of the stomach, which is maintained in the intestine. This prevents interaction of iron with other ligands, such as phytates, that bind iron at a higher pH .
-Cooking temperature does not affect the enhancing effect of animal tissue (Bæch et al., 2003b), although it may decrease the amount of haem iron by degradation into non-haem.
-Phytates, myo-inositol phosphates, present in whole-grain cereals and legumes, inhibit non-haem iron absorption.
-Polyphenols:black tea, green tea, coffee,chocolate, wine, herbs and spices, and seeds.
-Calcium and other divalent metals interact with iron for DMT-1 transport.
Iron bioavailability from food fortification to precision nutrition.A review