Iron Functions
Hemoglobin: green portion represents heme.
Iron is a mineral and an essential nutrient. Iron is a part of hemoglobin, the protein in our red blood cells that carries oxygen from our lungs to our cells. Without iron, hemoglobin cannot be made. Without enough hemoglobin, the amount of oxygen being carried to the cells is limited. Our cells cannot function efficiently without oxygen.
In the illustration to the right of hemoglobin, the red and blue ribbon-like structures represent protein sub-units. The green portion represents the iron containing portion of hemoglobin, called heme. Iron is a key component of heme and heme is the portion of hemoglobin that binds oxygen. Heme is the oxygen carrying portion of hemoglobin.
In the illustration to the right of hemoglobin, the red and blue ribbon-like structures represent protein sub-units. The green portion represents the iron containing portion of hemoglobin, called heme. Iron is a key component of heme and heme is the portion of hemoglobin that binds oxygen. Heme is the oxygen carrying portion of hemoglobin.
Iron Deficiency
This results from low dietary intake. Iron deficiency is “low iron stores” and can progress to iron deficiency anemia. Low iron levels cause fatigue and anemia. Blood loss can cause iron deficiency anemia Iron deficiency anemia is not the only type of anemia. The anemia associated with B12 deficiency (pernicious anemia) has no association with iron deficiency anemia. It is not recommended to take supplements unless recommended by a physician, it is possible to take in too much iron.
Iron Intake Recommendations
Age/Gender |
Amount of Iron |
infants 0-6 months |
0.27 mg |
infants 6-12 months |
11 mg |
children 1-3 |
7 mg |
children 4-8 |
10 mg |
males 9-13 years |
8 mg |
males 14-18 years |
11 mg |
males 19 and up |
8 mg |
females 9-13 years |
8 mg |
females 14-18 years |
15 mg |
females 19-50 years |
18 mg |
females 50 and up |
8 mg |
Dietary Sources of Iron
Very Good Sources of Heme Iron
- beef
- clams
- beef or chicken liver
- turkey
- chicken
- fish: halibut, tuna
- ham
- cooked beans
- tofu
- sesame or pumpkin seeds
- enriched cereal
- spinach
- swiss chard
- dried fruit
- baked potato
Iron Absorption
We only absorb about 10-20% of iron, on average, but this depends on the type of iron. Iron absorption may be as low as 2% or as high as 35% depending on the type of iron and food source. There is heme iron and non-heme iron. Look at the diagram above. You can see the iron surrounded by a circle, this is heme, the iron containing part of hemoglobin. Hemoglobin (and myoglobin) are the oxygen carrying proteins in animals. Therefore, when you eat an animal, you are eating hemoglobin, hence heme-iron. Iron also occurs in plants. But, plants don’t have hemoglobin, which means, the iron in plants is not bound to heme. We call plant iron non-heme iron.
Heme iron – animal iron
Some plant iron (non-heme) is poorly absorbed because of factors in the plant which inhibit iron absorption. I have a list of factors which increase iron absorption or decrease iron absorption on the next page. MFP factor, an enhancer, should be easy to remember, as it is an abbreviation for meat, fish and poultry.
Heme iron – animal iron
- Healthy people absorb heme iron at a rate of ≈23%
- Healthy people absorb non-heme iron at rates of 2%-20% (depending on the plant source)
Some plant iron (non-heme) is poorly absorbed because of factors in the plant which inhibit iron absorption. I have a list of factors which increase iron absorption or decrease iron absorption on the next page. MFP factor, an enhancer, should be easy to remember, as it is an abbreviation for meat, fish and poultry.
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When consuming a meal there will be many things that impact the bioavailability of iron. Bioavailability refers to the amount of iron in food that ends up being available in the body for use. To assess bioavailability you need to think about the type of iron (heme or non heme) and the factors that either inhibit or enhance iron absorption.
Vitamin C is a powerful enhancer of non-heme iron absorption and can even reverse the impact of phytates, tannins, calcium and phosphorus/phosphate. In your eTextbook, vitamin C is not in the list of enhancers, but stomach acid is. Stomach acid (hydrochloric acid) will free nutrients from food allowing them to be absorbed. This means that stomach acid will enhance both heme and non-heme iron absorption. |
Enhance Non-Heme Iron Absorption vitamin C (powerful!) meat, fish, poultry (MFP) factor Inhibit Non-Heme Iron Absorption tannins in tea, coffee & wine calcium and phosphorus phytates & fiber in grain phosvitin in eggs |
References
- Sizer, F. Whitney E. Water and Minerals. In: Nutrition Concepts and Controversies. 13 ed. Belmont, CA: Wadsworth. 2014.
- Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes, Elements. Food and Nutrition Board, Institute of Medicine, National Academies. United States Department of Agricultural. Last accessed March 23, 2016. https://fnic.nal.usda.gov/sites/fnic.nal.usda.gov/files/uploads/recommended_intakes_individuals.pdf
- Food Sources. Iron. Minerals. Linus Pauling Institute Micronutrient Information Center. http://lpi.oregonstate.edu/mic/minerals/iron Last updated August, 2009. Last accessed April 13, 2016.
- Hemoglobin image by Zephyris on Wikipedia, CC BY-SA 3.0.
- Raw meat header by Fried C on Wikipedia, CC0 1.0.
Last updated April 2nd, 2016