Health Library Explorer
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z Listings Contact Us


Other name(s):

carbonyl iron, desiccated ferrous sulfate, ferrous fumarate, ferrous gluconate, ferrous sulfate

General description

Iron is an essential mineral. It’s needed for red blood cells to form. Red blood cells carry oxygen to all parts of the body. But iron is toxic in large doses. Iron overdose is the number one cause of poisoning in children in the U.S.

Iron works as the oxygen-carrying part of hemoglobin. This is the red pigment inside red blood cells that gives blood its color. Iron is stored by the body in the liver, spleen, and bone marrow. Iron is also needed for myoglobin to form. Myoglobin is found in muscle tissue. It supplies oxygen to working muscle cells. It also helps with muscle contraction.

Iron helps to maintain the health of red blood cells and muscle tissue. It also helps make collagen and plays an important role in how the immune system functions.

Medically valid uses

Iron supplements are mainly used to treat iron-deficiency anemia.

Pica can sometimes be treated with iron supplements. This condition causes a craving for nonfood items, such as mud, clay, laundry starch, chalk, paint chips, or ashes. Pica often occurs due to an iron deficiency. It’s also seen in pregnant women and small children with developmental issues, such as autism.

If you have depressed immune function due to an iron deficiency, supplements can help.

Unsubstantiated claims

There may be benefits that have not yet been proven through research.

Iron may stimulate the immune system. It may also treat alcoholism. It’s been claimed to boost athletic performance. Always work with a healthcare provider before supplementing with iron because of its toxic effects when too much is taken.

Recommended intake

Iron is in many foods naturally. It is also added to some foods and is available as a supplement. Many health issues and procedures increase the need for iron. These include:

  • Recently lost or donated a lot of blood

  • Very heavy menstrual flow

  • Hemodialysis

  • Burns

  • Decreased acid production (achlorhydria)

  • Surgery to remove part or all of your stomach (gastrectomy)

  • Issues that cause ongoing blood loss, such as hemorrhoids, peptic ulcer, or hookworms

  • Intestinal bleeding due to aspirin and arthritis medicines

Athletes may also need more iron. This is due to larger losses of iron in sweat. Athletes also make more hemoglobin.

Women who are pregnant or breastfeeding may need to take supplements. But you should always talk to your healthcare provider before doing so. Low iron levels during pregnancy increase the chance of premature and low-birth-weight babies.

Iron is measured in milligrams (mg). The Recommended Dietary Allowance (RDA) is:



Infants (0 to 6 months)

0.27 mg*

Infants (7 months to 1 year)

11 mg

Children (1 to 3 years)

7 mg

Children (4 to 8 years)

10 mg

Children (9 to 13 years)

8 mg

Males (14 to 18 years)

11 mg

Females (14 to 18 years)

15 mg

Males (19 years and older)

8 mg

Females (19 to 50 years)

18 mg

Females (51 years and older)

8 mg

Pregnant women

27 mg

Breastfeeding women (14 to 18 years)

10 mg

Breastfeeding women (19 years and older)

9 mg

*Adequate intake

Iron supplements come in different forms. Some forms have been made to decrease the gastrointestinal side effects, such as constipation. Each form has a different amount of iron. Ferrous fumarate and ferrous sulfate contain the highest amounts of iron. Ferrous gluconate has the lowest.

Dosage is noted either as the amount of iron or the percentage of iron. Read the label closely. For example, 325 mg of ferrous sulfate contains only 65 mg of elemental iron.

Carbonyl iron is a form of elemental iron. It’s been very finely ground. This improves how well it’s absorbed. It’s one of the safer forms of iron.

Heme iron is absorbed the best. This is found in red meat and poultry. Taking vitamin C with foods high in iron helps your body absorb iron better, especially from nonheme sources.

For the gastrointestinal system to absorb iron, the stomach needs to be acidic. Certain antacids, such as calcium bicarbonate, can change the pH level of the stomach. It can make it very alkaline. This means that too much use of antacids may interfere with iron uptake.


Nutrient Content per 100 grams

Brewer's yeast

17.3 mg


11.8 mg

Wheat germ

9.4 mg


8.6 mg

Pistachio nuts

7.3 mg

Egg yolks

7.2 mg

Beef liver

6.5 mg


6.2 mg

Kidney beans

6.1 mg


5.5 mg

Baker's yeast

4.9 mg


3.2 mg

Pork and ham (varies with cut, doesn’t include organs)

2.5 mg

White enriched bread

0.5 mg


1.8 mg

Not having enough iron in your body can lead to anemia. It’s most likely to cause microcytic hypochromic anemia. This condition causes red blood cells to be smaller than normal. They also don’t contain a normal amount of hemoglobin. This type of anemia may cause symptoms. These can include weakness, pale-colored skin and fingernails, cold hands and feet, severe tiredness (fatigue), dizziness, shortness of breath, and headache.

Mild iron deficiency may lead to pica. This tends to cause a hunger for ice and, in some areas of the country, clay. It’s often seen in pregnant women. Note that pica in young children isn’t due to iron deficiency in most cases.

Side effects, toxicity, and interactions

Iron is very toxic in large amounts. In just 3 to 4 days, toxic levels of iron can cause death. In a severe overdose, iron quickly destroys the lining of the intestinal tract. It may lead to holes in the intestine. Free iron ions in the bloodstream destroy the lining of the blood vessels (endothelium). This leads to irreversible shock. Too much iron can also cause severe liver damage.

Iron supplements, including prenatal and children's vitamins, often come as brightly colored tablets. Young children find these attractive. They may attempt to eat an entire bottle. Because iron is very toxic and large overdoses can be fatal, it’s important to store iron supplements out of the reach of children. Close to 100% of iron poisonings happen in children. Iron is the leading cause of fatal poisoning in children.

Iron can also cause side effects at normal doses. These can include constipation or black stool. Taking a stool softener may help.

Taking daily doses of iron above the recommended amount may cause iron to build up in your body. This can lead to iron overload. This harms the liver and causes cirrhosis. It can also damage the heart, pancreas, pituitary gland, and other organs. This condition is called acquired hemochromatosis.

Taking in too much iron is also linked with heart disease. Studies are also looking at whether too much iron plays a role in some types of cancer.

Many blood diseases can cause anemia. Taking iron supplements can mask these issues. This can cause them to go undiagnosed. Some blood diseases, if treated with iron, may cause iron overload. They include:

  • Sickle cell anemia

  • Glucose-6-phosphate dehydrogenase deficiency

  • Hereditary spherocytosis

  • Hereditary elliptocytosis

  • Pyruvate kinase deficiency

  • Acquired or genetic hemochromatosis

  • Thalassemia

Iron supplements often contain tartrazine or sulfites. People who are allergic to aspirin have a higher sensitivity to tartrazine. People who have asthma are more likely to be allergic to sulfites. People with these conditions should talk to their healthcare providers before taking an iron supplement.

Iron interacts with many medicines. Antacids can decrease how much iron your body absorbs. So can cimetidine, a medicine that blocks the production of stomach acid. This means iron supplements won’t work as well. Ascorbic acid (vitamin C) increases how much iron is absorbed. The antibiotic chloramphenicol increases the levels of iron in your body.

Any medicine in the tetracycline family will bind with iron. This will decrease the absorption of both the medicine and iron. Iron also interferes with levodopa, methyldopa, etidronate, levothyroxine, penicillamine, and quinolone antibiotics. Iron decreases how well these medicines work.

Eggs, dairy foods, and drinks, such as coffee and tea, can decrease iron absorption. You shouldn’t take iron within 2 hours of eating these foods. Calcium, fiber, tannin (found in tea), soy protein, and oxalic acid (found in some vegetables) can keep your body from absorbing iron.

Additional information

Genetic hemochromatosis is a common issue where the body absorbs and stores extra iron. Over time, this buildup may lead to organ damage, especially in the liver. In most cases, symptoms don’t show up until after age 40. This disease is seen almost 10 times as often in men (about 1.5 per 1,000) than women. This is because women tend to lose iron through menstruation. Men should be careful about taking iron supplements. A healthy diet will often supply a man with enough iron.

Online Medical Reviewer: Bianca Garilli MD
Online Medical Reviewer: Chris Southard RN
Online Medical Reviewer: Stacey Wojcik MBA BSN RN
Date Last Reviewed: 8/1/2023
The health content and information on this site is made possible through the generous support of the Haspel Education Fund.
StayWell Disclaimer