There are 2 major dietary forms of iron: heme iron and non-heme iron. Heme iron is only found in foods of animal origin, within hemoglobin and myoglobin. The structure of heme iron is shown below.
Approximately 40% of iron in meat, fish, and poultry is heme-iron, and the other 60% is non-heme iron2.
Non-heme iron is the mineral alone, in either its oxidized or reduced form. The 2 forms of iron are:
Ferric (Fe3+, oxidized)
Ferrous (Fe2+, reduced)
It is estimated that 25% of heme iron and 17% of non-heme iron are absorbed2. Approximately 85-90% of the iron we consume is non-heme iron2,3.
In addition to getting iron from food sources, if food is cooked in cast iron cookware, a small amount of iron can be transferred to the food. The story below is an iron fish that is being used in Cambodia to increase iron intake in an area with prevalent iron deficiency. However, they found that the iron fish was not effective in reducing anemia4.
Many breakfast cereals are fortified with reduced iron, which looks like iron filings, as the following video shows.
While the iron bioavailability of this reduced iron is low, some is absorbed5.
Most iron supplements use ferrous (Fe2+) iron, because this form is better absorbed, as discussed in the next section. The figure below shows the percent of elemental iron in different supplements. This is the percentage of elemental iron that is in each compound.
Vitamin C does not increase absorption of ferrous supplements because they are already in reduced form, as discussed in the following subsection2. Iron chelates are marketed as being better absorbed than other forms of iron supplements, but this has not been proven6. It is recommended that supplements are not taken with meals, because they are better absorbed when not consumed with food2.
References & Links
2. Whitney E, Rolfes SR. (2011) Understanding nutrition. Belmont, CA: Wadsworth Cengage Learning.
4. Rappaport AI, Whitfield KC, Chapman GE, Yada RY, Kheang KM, Louise J, Summerlee AJ, Armstrong GR, Green TJ. Randomized controlled trial assessing the efficacy of a reusable fish-shaped iron ingot to increase hemoglobin concentration in anemic, rural Cambodian women. (2017) Am J Clin Nutr 106 (2): 667-674.
5. Garcia-Casal M, Layrisse M, Pena-Rosas J, Ramirez J, Leets I, et al. (2003) Iron absorption from elemental iron-fortified corn flakes in humans. role of vitamins A and C1-3. Nutr Res 23(4): 451-463.
6. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
Canadian’s lucky iron fish saves lives in Cambodia – http://www.therecord.com/news/local/article/624229–canadian-s-lucky-iron-fish-saves-lives-in-cambodia
Iron for breakfast – https://www.youtube.com/watch?v=pRK15XSqtAw