The human body has an amazing ability to take the vitamins and minerals it needs from a variety of sources. When you eat iron-rich foods, your body absorbs the iron it needs during the digestion process.
The percentage of iron absorbed from food (known as iron bioavailability) varies, but it can range from 1% to 50%.1 Usually, the factor that has the greatest effect on absorption is the amount of iron your body already has stored.2 However, absorption can also be affected by the type of iron you ingest, and what other foods you eat at the same time.3,4
For more information about iron and the absorption process, read:
1 Finch CA, Cook JD. Iron deficiency. Am J Clin Nutr. 1984;39(3):471-477.
2 Centers for Disease Control and Prevention. Recommendations to prevent and control iron deficiency in the United States. MMWR Recomm Rep. 1998;47(RR-3):1-36. http://www.cdc.gov/MMWR/preview/mmwrhtml/00051880.htm. Accessed November 2, 2012.
3 Barton JC. Iron deficiency. In: Rakel RE, Bope ET, eds. Conn’s Current Therapy. Amsterdam, the Netherlands: Saunders/Elsevier; 2008:385-389.
4 Lynch SR, Stoltzfus RJ. Iron and ascorbic Acid: proposed fortification levels and recommended iron compounds. J Nutr. 2003;133(9):2978S-2984S.