Iron: Functions, Food Sources, and More
By Lizzie Streit, MS, RDN, LD
Iron is an extremely important nutrient that plays several roles in the body and is found in many foods. It is a vital part of the proteins that transfer oxygen and is necessary for proper growth and cell functioning.
Despite the fact that iron is widespread in foods, iron deficiency is one of the most common nutrient deficiencies in the world (1, 2).
Knowing how iron works in the body and what foods contain this mineral is important for preventing and treating iron deficiency.
This post provides an overview of everything you need to know about iron: functions, food sources, and more!
Functions of Iron
Iron is necessary for the creation of hemoglobin, a protein in red blood cells that transfers oxygen from the lungs to the tissues. It is also a vital component of myoglobin, the protein that delivers oxygen to muscles (1, 3).
The functions of iron in the body highlight how important it is in maintaining energy. Inadequate levels or absorption of iron causes low energy levels and a number of negative consequences.
Types and Absorption of Iron
The two main types of dietary iron are heme and nonheme.
Nonheme iron is found in plant foods, such as legumes, whole grains, nuts and seeds, and some vegetables, as well as iron-fortified products. On the other hand, both nonheme and heme iron are found in animal products, such as meat, seafood, and eggs.
Heme iron is better absorbed than nonheme iron. Vitamin C, also known as ascorbic acid, enhances the absorption of iron. Some compounds, such as phytates found in grains and beans and polyphenols in tea and coffee, inhibit the absorption of iron (3, 4).
Eating a variety of foods that contain both heme and nonheme iron, as well as foods that are rich in vitamin C, can help you meet your iron needs. Fruits and vegetables with vitamin C include brussels sprouts, bell peppers, citrus fruits, broccoli, and more.
Iron Deficiency: Populations at Risk, Signs, and Symptoms
Iron deficiency occurs as the result of inadequate intake or absorption.
In the United States, most people consume enough iron from their diets, but iron deficiency is still common in certain population groups. Those at risk of iron deficiency include (1):
Pregnant women: iron needs increase during pregnancy as expecting mothers undergo increased red blood cell production
Women with heavy periods: heavy menstrual bleeding can cause significant iron loss
Infants and children: rapid growth in childhood increases the need for iron, especially in children who were born to iron-deficient mothers
Blood donors: giving blood on a regular basis can deplete iron stores
People with GI disorders or who have had surgeries that impact the GI tract: those with celiac disease, ulcerative colitis, or Crohn’s disease, as well as people who have had parts of their GI tract resected, may not absorb iron properly or suffer from blood loss
People with cancer: chemotherapy and the cancer disease process can lead to iron deficiency anemia
Iron deficiency is incredibly common in developing countries. This is mainly due to the high rate of parasite infections that affect the GI tract and result in blood loss, and the lack of access to iron-rich foods or foods that contain iron in a more absorbable form (heme).
Signs and symptoms of iron deficiency include:
Extreme fatigue
Fast heartbeat
Lightheadedness or dizziness
Having cold hands or feet
Brittle nails
Pale skin
If iron deficiency is not treated, it can lead to weakened immunity and cognitive delays, especially in infants and young children.
Iron Toxicity: Populations at Risk, Signs, and Symptoms
While there is a very low risk of getting too much iron from food sources, it is possible to consume excessive iron from supplements.
Severe overdoses of iron supplements can lead to coma and even death. Therefore, it is especially important to keep iron supplements out of reach of children who may accidentally ingest them.
The tolerable upper intake levels (ULs) for iron are 40 mg for infants and children up to 13 years of age, and 45 mg for those over 14 years of age (1).
People who have hemochromatosis may also be at risk of iron toxicity. Hemochromatosis is a genetic condition that leads to the buildup of iron in the body. It is treated with phlebotomy as well as a diet that avoids iron-rich foods and vitamin C supplements.
Signs and symptoms of iron toxicity include (5):
Nausea and vomiting
Diarrhea
Stomach pain
Recommended Intakes of Iron
The Recommended Dietary Allowances (RDAs) for iron are (1):
0 to 6 months: 0.27 mg
7-12 months: 11 mg
1-3 years: 7 mg
4-8 years: 10 mg
9-13 years: 8 mg
14-18 years: 11 mg (male), 15 mg (female)
19-50 years: 8 mg (male), 18 mg (female)
51+ years: 8 mg
Pregnancy: 27 mg
Lactation: 10 mg
Food Sources
The best way to maintain adequate iron levels is to consume iron-rich foods.
Keep in mind that animal foods contain both heme and nonheme iron, while plant foods only contain nonheme iron, which is not as well absorbed.
Below is a list of foods that are rich in iron and the amount of iron they contain (6):
Ground beef (3 ounces): 2.2 mg
Egg (1 large): 0.8 mg
Chicken breast (3 ounces): 0.5 mg
Salmon (3 ounces): 0.4 mg
Shrimp (3 ounces): 0.4 mg
Quinoa (1 cup): 2.8 mg
Black beans (1/4 cup): 2.7 mg
Sunflower seeds (1/4 cup): 1.8 mg
Almonds (1/4 cup): 1.3 mg
Garbanzo beans (1/4 cup): 1 mg
Brussels sprouts (1 cup, cooked): 1.9 mg
Spinach (2 cups, raw): 1.6 mg
Broccoli (1 cup, raw): 0.7 mg
As noted above, vitamin C enhances absorption of iron. Foods that are high in vitamin C include:
Citrus fruits: grapefruit, oranges, lemon, limes
Brussels sprouts
Bell peppers
Tomatoes
Sweet potatoes
Kale
Strawberries
Broccoli
Some people may need iron supplements, even if they consume a variety of iron-rich foods. If you think you are at risk of iron deficiency, check with your healthcare provider about taking a supplement.
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