Iron deficiency anemia is the world's most common nutritional deficiency disease and is most prevalent among children and women of childbearing age.
This type of anemia develops due to an inadequate amount of iron in the diet, impaired iron absorption, acute blood loss caused by hemorrhage or injury, or gradual blood loss such as from menstruation or gastrointestinal bleeding.
Inadequate intake of vitamin C can also contribute to iron deficiency as vitamin C is needed to absorb iron found in plant foods (non-heme iron).
Iron-deficiency anemia should not be confused with megaloblastic anemia which results from inadequate intake and/or utilization of folate and vitamin B12. Pernicious anemia is a form of megaloblastic anemia caused by a lack of a substance called intrinsic factor in the stomach that results in poor absorption of vitamin B12.
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 iron.
Contents of this article:
The Recommended Daily Allowance (RDA) for iron depends on a person's age and sex.
Inadequate intake of folate, protein and vitamin C can contribute to iron deficiency.
- 0-6 months: 0.27 milligrams (adequate intake, or AI)
- 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
- 19 years and older: 8 mg.
- 9-13 years: 8 mg
- 14-18 years: 15 mg
- 19-50 years: 18 mg
- 51 years and older: 8 mg.
- Pregnancy: 27 mg
- Lactation 14-18 years: 10 mg
- Lactation 19 years and older: 9 mg.
An estimated 8 million women of childbearing age in the US suffer from iron deficiency severe enough to cause anemia. Iron deficiency during pregnancy may raise the risk for preterm delivery.
Iron supplements can be helpful where people find it difficult to achieve adequate iron status through diet alone. It is, however, preferable to try to achieve optimal iron status by including iron-rich foods in the diet and by removing or reducing factors that may hinder iron absorption. This is because many of the foods that are rich in iron also contain a range of other beneficial nutrients that work together to support overall health.
Possible health benefits of consuming iron
Iron deficiency can cause many health problems, including impaired cognitive function, gastrointestinal disturbances, poor exercise and work performance, lowered immune function and poor body temperature regulation.
Iron deficiency anemia and iron dysregulation are associated with conditions such as rheumatoid arthritis (RA) and Lupus Erythematosus.7
In children, iron deficiency anemia can cause psychomotor and cognitive abnormalities resulting in future learning difficulties.
Blood volume and red blood cell production increases dramatically during pregnancy in order to supply the growing fetus with oxygen and nutrients. As such, the demand for iron also increases. While the body typically upregulates iron absorption during pregnancy, insufficient iron intake or other factors affecting iron absorption or utilization can lead to iron deficiency.
Low iron status 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.
Not getting enough iron in your diet can affect how efficiently your 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 sedentary individuals. Iron deficiency in athletes decreases athletic performance and weakens immune system activity. A lack of hemoglobin can greatly reduce physical work performance as it decreases the body's ability to transport oxygen to the muscles.
Foods high in iron
Iron has a low bioavailability, meaning that it has poor absorption within the small intestine and low retention in the body, decreasing its availability for use. The efficiency of absorption depends on the source of iron, other components of the diet, gastrointestinal health, use of medications or supplements, and a person's overall iron status. In many countries, wheat products and infant formulas are fortified with iron.
There are two types of dietary iron - heme and non-heme. Most animal products, including seafood, contain both non-heme and heme iron, with the latter easier to absorb as it is bound to protoporphyrin IX. Non-heme iron sources include beans, nuts, vegetables and fortified grains.
The recommended iron intake for vegetarians is 1.8 times higher than for those who eat meat in order to make up for the lower absorption level from plant-based foods. The bioavailability of iron from omnivorous diets that include meat, seafood, and vitamin C is around 14-18%, while iron bioavailability from a vegetarian diet is around 5-12%.4,5 Consuming vitamin C-rich foods alongside non-heme sources of iron can dramatically increase iron absorption.
Non-heme iron absorption is inhibited by:
- Proton pump inhibitors (lansoprazole [Prevacid®] and omeprazole [Prilosec®]) 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.
Both heme and non-heme iron absorption may be impaired by calcium. Typically, a varied western-style diet is considered balanced in terms of enhancers and inhibitors of iron absorption.
Clams contain a significant 24 mg of iron per 3 oz.
Some of the best sources of iron include:
- Clams, canned, 3 oz: 24 milligrams
- Cereal, fortified, one serving: 1-22 milligrams
- White beans, canned, 1 cup: 8 milligrams
- Chocolate, dark, 45-69% cacao, 3 oz: 7 milligrams
- Oysters, cooked, 3 oz: 6 milligrams
- Spinach, cooked, 1 cup: 6 milligrams
- Beef liver, 3 oz: 5 milligrams
- Blueberries, frozen, ½ cup: 5 milligrams
- Lentils, boiled and drained, ½ cup: 3 milligrams
- Tofu, firm, ½ cup: 3 milligrams
- Chickpeas, boiled and drained, ½ cup: 2 milligrams
- Tomatoes, canned, stewed, ½ cup: 2 milligrams
- Ground beef, lean, 3 oz: 2 milligrams
- Potato, baked, medium: 2 milligrams
- Cashew nuts, roasted, 1 oz: 2 milligrams
- Egg, 1 large: 1 milligram.1,2
Potential health risks of consuming iron
The tolerable upper intake level for iron is between 40-45 milligrams. Adults with a healthy functional gastrointestinal system have a very low risk of iron overload from dietary sources.
People with a genetic disorder called hemochromatosis are at a high risk of iron overload as they absorb three to four times more iron from food compared to people without the condition.8 This can lead to a build-up of iron in the liver and other organs, and the creation of free radicals that damage cells and tissues including the liver, heart and pancreas, in addition to increasing the risk of cancer.8
Around 10% of white people of Northern European ancestry carry the most common hemochromatosis gene (HFE) mutation (C282Y), but only around 0.044% of white people carry two copies of the mutated gene, resulting in hemochromatosis.8 People of other ethnicities are much less likely to have hemochromatosis.
Taking iron supplements of 20 milligrams or more on a frequent basis 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, coma, seizure, and even death. It is important to keep iron supplements out of reach of children so as to reduce the risk of fatal overdose.
Accidental ingestion of iron supplements were responsible for about a third of poisoning deaths among children in the US between 1983 and 1991, and some 43 deaths between 1983 and 2000.
Changes in the manufacture and distribution of iron supplements, such as replacing sugar coatings on iron tablets with film coatings, using child-proof bottle caps, and individually packaging high doses of iron have all helped to reduce accidental iron overdoses in children. Just one death from iron overdose was reported between 1998 and 2002.
Some studies have suggested that excessive iron intake can increase the risk of coronary heart disease and cancer. More recently, scientists have begun investigating the possible role of excess iron in the development and progression of diseases such as multiple sclerosis and arthritis.6
Preliminary research indicates that adequate iron is needed to help protect the nervous system and joints in these conditions, while abnormalities in iron metabolism may lead to an increase in oxidative damage and inflammation that damages tissues.9
Iron plays a key role in oxidative stress and photo-induced skin damage due to the generation of reactive oxygen species (ROS) by ultraviolet (UVA) and iron.7
Iron overload can lead to the formation of iron deposits in the skin and to complications of venous disease and hereditary hemochromatosis.7
Iron supplements can interact with several medications, including levodopa (used to treat restless leg syndrome and Parkinson's disease) and levothyroxine (used to treat hypothyroidism, goiter, and thyroid cancer).
Anyone considering taking an iron supplement should first discuss this with their physician or health care practitioner as some of the signs of iron overload can look quite similar to those of iron deficiency. An excess of iron can be dangerous, and iron supplements are not recommended except in cases of diagnosed deficiency or where a person is at risk of developing iron deficiency.
Attempting to achieve optimal iron intake and status through dietary means is preferable in order to minimize the risk of iron overdose and ensure a good intake of other beneficial nutrients found alongside iron in foods.