Iron is a mineral vital to the proper function of hemoglobin, a protein needed to transport oxygen in the blood. Iron also has a role in a variety of other important processes in the body.
A shortage of iron in the blood can lead to a range of serious health problems, including iron deficiency anemia. Around 10 million people in the United States have low iron levels, and roughly 5 million of these have been diagnosed with iron deficiency anemia.
This MNT Knowledge Center feature is part of a collection of articles on the health benefits of popular vitamins and minerals. It provides an in-depth look at recommended intake of iron, its possible health benefits, foods high in iron, and any potential health risks of consuming too much iron.
Fast facts on iron
- The Recommended Daily Allowance (RDA) varies between ages, but women who are pregnant require the most.
- Iron promotes healthy pregnancy, increased energy, and better athletic performance. Iron deficiency is most common in female athletes.
- Canned clams, fortified cereals, and white beans are the best sources of dietary iron.
- Too much iron can increase the risk of liver cancer and diabetes.
The Recommended Daily Allowance (RDA) for elemental iron depends on a person’s age and sex. Vegetarians also have different iron requirements.
- 0 to 6 months: 0.27 milligrams (mg)
- 7 to 12 months: 11 mg
- 1 to 3 years: 7 mg
- 4 to 8 years: 10 mg
- 9 to 13 years: 8 mg
- 14 to 18 years: 11 mg
- 19 years and older: 8 mg
- 9 to 13 years: 8 mg
- 14 to 18 years: 15 mg
- 19 to 50 years: 18 mg
- 51 years and older: 8 mg
- During pregnancy: 27 mg
- When lactating between 14 and 18 years of age: 10 mg
- When lactating at older than 19 years: 9 mg
Iron supplements can be helpful when people find it difficult to take in enough iron through only dietary measures, such as in a plant-based diet. It is better to try to consume enough in the diet alone by removing or reducing factors that may hinder iron absorption and consuming iron-rich foods.
This is because many iron-rich foods also contain a range of other beneficial nutrients that work together to support overall health.
Iron helps to preserve many vital functions in the body, including general energy and focus, gastrointestinal processes, the immune system, and the regulation of body temperature.
The benefits of iron often go unnoticed until a person is not getting enough. Iron deficiency anemia can cause fatigue, heart palpitations, pale skin, and breathlessness.
Blood volume and red blood cell production increase dramatically during pregnancy to supply the growing fetus with oxygen and nutrients. As a result, the demand for iron also increases. While the body typically maximizes iron absorption during pregnancy, insufficient iron intake or other factors affecting the way iron is absorbed can lead to iron deficiency.
Low iron intake during pregnancy increases the risk of premature birth and low birth weight, as well as low iron stores and impaired cognitive or behavioral development in infants. Pregnant women with low iron may be more prone to infection because iron also supports the immune system.
It is clear that iron supplements are needed for women who are both pregnant and iron-deficient. However, research is ongoing as to the possibility of recommending additional iron to all pregnant women, even those with normal iron levels. It is argued that all pregnant women should take 30 to 60 milligrams (mg) of iron supplements on every day of their pregnancy, regardless of their iron levels.
Insufficient iron in the diet can affect the efficiency with which the body uses energy. Iron carries oxygen to the muscles and brain and is crucial for both mental and physical performance. Low iron levels may result in a lack of focus, increased irritability, and reduced stamina.
Better athletic performance
Iron deficiency is more common among athletes, especially young female athletes, than in individuals who do not lead an active lifestyle.
This appears to be particularly true in female endurance athletes, such as long-distance runners. Some experts suggest that female endurance athletes should add an additional 10 mg of elemental iron per day to the current RDA for iron intake.
Iron deficiency in athletes decreases athletic performance and weakens immune system activity. A lack of hemoglobin can greatly reduce performance during physical exertion, as it decreases the body’s ability to transport oxygen to the muscles.
Iron has a low bioavailability, meaning that the small intestine does not readily absorb large amounts. This decreases its availability for use and increases the likelihood of deficiency.
The efficiency of absorption depends on a range of factors, including:
- the source of iron
- other components of the diet
- gastrointestinal health
- use of medications or supplements
- a person’s overall iron status
- presence of iron promoters, such as vitamin C
In many countries, wheat products and infant formulas are fortified with iron.
There are two types of dietary iron, known as heme and non-heme. Animal sources of food, including meat and seafood, contain heme iron. Heme iron is more easily absorbed by the body.
Non-heme iron, the type found in plants, requires that the body take multiple steps to absorb it. Plant-based sources of iron include beans, nuts, soy, vegetables, and fortified grains.
The bioavailability of heme iron from animal sources can be up to 40 percent. Non-heme iron from plant-based sources, however, has a bioavailability of between 2 and 20 percent. For this reason, the RDA for vegetarians is 1.8 times higher than for those who eat meat to make up for the lower absorption level from plant-based foods.
Consuming vitamin-C-rich foods alongside non-heme sources of iron can dramatically increase iron absorption.
When following a vegetarian diet, it is also important to consider components of food and medications that block or reduce iron absorption, such as:
- proton pump inhibitors and omeprazole, used to reduce the acidity of stomach contents
- polyphenols in cereals and legumes, as well as in spinach
- tannins in coffee, tea, some wine, and certain berries
- phosphates in carbonated beverages, such as soda
- phytates in beans and grains
Some of the best sources of iron include:
- Canned clams: 3 ounces (oz) provides 26 milligrams (mg) of iron.
- Fortified, plain, dry cereal oats: 100 g provides 24.72 mg.
- White beans: One cup provides 21.09.
- Dark chocolate (45 to 69 percent cacao): One bar provides 12.99 mg.
- Cooked Pacific oysters: 3 oz provides 7.82 mg.
- Cooked spinach: One cup provides 6.43 mg.
- Beef liver: 3 oz provides 4.17 mg.
- Boiled and drained lentils: Half a cup provides 3.3 mg.
- Firm tofu: Half a cup provides 2.03 mg.
- Boiled and drained chickpeas: Half a cup provides 2.37 mg.
- Canned, stewed tomatoes: Half a cup provides 1.7 mg.
- Lean, ground beef: 3 oz provides 2.07 mg.
- Medium baked potato: This provides 1.87 mg.
- Roasted cashew nuts: 3 oz provides 2 mg.
Calcium can slow both heme and non-heme iron absorption. In most cases, a typical varied, Western-style diet is considered balanced in terms of enhancers and inhibitors of iron absorption.
In adults, doses for oral iron supplementation can be as high as 60 to 120 mg of elemental iron per day. These doses typically apply to women who are pregnant and severely iron-deficient. An upset stomach is a common side effect of iron supplementation, so dividing doses throughout the day may help.
Adults with a healthy digestive system have a very low risk of iron overload from dietary sources.
This can lead to a buildup of iron in the liver and other organs. It can also cause the creation of free radicals that damage cells and tissues, including the liver, heart, and pancreas, as well increasing the risk of certain cancers.
Frequently taking iron supplements that contain more than 20 mg of elemental iron at a time can cause nausea, vomiting, and stomach pain, especially if the supplement is not taken with food. In severe cases, iron overdoses can lead to organ failure, internal bleeding, coma, seizure, and even death.
It is important to keep iron supplements out of reach of children to reduce the risk of fatal overdose.
According to Poison Control, accidental ingestion of iron supplements was the most common cause of death from an overdose of medication in children less than 6 years old until the 1990s.
Changes in the manufacture and distribution of iron supplements have helped reduce accidental iron overdoses in children, such as replacing sugar coatings on iron tablets with film coatings, using child-proof bottle caps, and individually packaging high doses of iron. Only one death from an iron overdose was reported between 1998 and 2002.
More recently, scientists have begun investigating the possible role of excess iron in the development and progression of neurological diseases, such as Alzheimer’s disease, and Parkinson’s disease. Iron may also have a direct damaging role in brain injury that results from bleeding within the brain. Research in mice has shown that high iron states increase the risk of osteoarthritis.
Iron supplements can decrease the availability of several medications, including levodopa, which is used to treat restless leg syndrome and Parkinson’s disease and levothyroxine, which is used to treat a low-functioning thyroid.
Proton pump inhibitors (PPIs) used to treat reflux disease can reduce the amount of iron that can be absorbed by the body from both food and supplements.
Discuss taking an iron supplement with a physician or healthcare practitioner, as some of the signs of iron overload can resemble those of iron deficiency. Excess iron can be dangerous, and iron supplements are not recommended except in cases of diagnosed deficiency, or where a person is at high risk of developing iron deficiency.
It is preferable to achieve optimal iron intake and status through the diet rather than supplements. This can help minimize the risk of iron overdose and ensure a good intake of the other nutrients found alongside iron in foods.