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12.7: Iron

There are two 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.

Figure 12.71 Structure of heme iron1

Approximately 40% of iron in meat, fish, and poultry is heme-iron, and the other 60% is non-heme iron2Non-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. 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 are absorbed4.


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.

Figure 12.72 Elemental iron in different iron supplements3

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 proven5. 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. 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.
  5. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.