Iron: Benefits, Side Effects, Dosage, and Interactions (2023)

Iron has many benefits and is one of the most important minerals for your body. Iron is needed for your body to produce hemoglobin, which helps red blood cells (RBCs) carry oxygen throughout the body, and myoglobin, which is a protein that helps provide oxygen to the cells in your muscles.

While all human cells contain iron, it is mostly found in RBCs.

Iron supplements play a vital role in treating anemia (low levels of healthy RBCs), particularly iron deficiency anemia (IDA). Most people get all the iron they need from their diets. However, some may be prone to iron deficiency. Iron deficiency is the most common cause of anemia, occurring in 5% of women and 2% of men.

This article explains what iron does for your body and when iron supplementation might be appropriate.

Dietary supplements are not regulated in the United States, meaning the Food and Drug Administration (FDA) does not approve them for safety and effectiveness before products are marketed. When possible, choose a supplement that has been tested by a trusted third party, such as USP, ConsumerLabs, or NSF. However, even if supplements are third-party tested, that doesn't mean they are necessarily safe for all or effective in general. It is important to talk to your healthcare provider about any supplements you plan to take and to check in about any potential interactions with other supplements or medications.

Supplement Facts

  • Active ingredient: Iron
  • Alternate name(s): Ferrous sulfate, ferrous gluconate, ferric citrate, ferric sulfate
  • Recommended Dose: Recommended dietary allowance ranges 7-27 milligrams per day depending on age and gender, tolerable upper limit ranges are 40-45 milligrams per day, treatment for iron deficiency anemia is 50-100 milligrams per day divided into separate doses
  • Safety Considerations: Discuss with a healthcare provider regarding proper dose before taking. Avoid exceeding the tolerable upper limit for iron unless recommended to treat iron deficiency, accidental iron poisoning has occurred in young children. Keep adult supplements and medications out of children's reach.

Uses of Iron

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or doctor. No supplement is intended to treat, cure, or prevent a disease.

Iron supplementation primarily works to restore low iron levels. Treating iron deficiency alleviates the symptoms you could experience with low iron and anemia. It also helps to prevent complications down the road as iron deficiency progresses to anemia.

Iron supplementation has no benefit in people who do not have an iron deficiency.


Iron supplementation is helpful for anemia caused by iron deficiency. There are several different causes of anemia, but iron deficiency is the most common. Anemia results when iron deficiency progresses to the point that hemoglobin (a protein in red blood cells) levels drop to below normal levels.

Iron deficiency can lead to arrhythmias, heart murmur, enlarged heart, and heart failure if left untreated. Iron deficiency may also be associated with an increased risk of fibromyalgia.

Iron supplementation can improve iron levels and treat IDA. Daily iron supplementation has been shown to reduce the prevalence of anemia and low iron status in menstruating individuals.

Iron deficiency is the most common nutrient deficiency. Left untreated, it can lead to numerous health issues. If you suspect you may be deficient, discuss with your healthcare provider so that a deficiency can be appropriately confirmed and treated.


Iron may help manage unexplained fatigue, even in someone who isn’t anemic but has a low ferritin level (an indicator of iron stores). This is especially common in women during their reproductive years. Daily iron supplementation may reduce fatigue in menstruating women.

A randomized trial studied women aged 18 to 53 years who reported experiencing fatigue. Women with a ferritin less than 50 micrograms per liter (mcg/L) and hemoglobin greater than 12 grams per deciliter were randomized to receive either 80 milligrams (mg) of elemental iron or placebo. The group receiving iron reported greater improvement in fatigue but no improvement in overall quality of life.

Iron supplementation may improve fatigue in women with low ferritin levels.

Athletic Performance

Iron is needed to make myoglobin, the protein that provides oxygen to the muscles. Many athletes may have inadequate iron intake from their diet to support performance.

However, athletes involved in endurance training like marathon running or endurance cycling events can lose more iron. Additionally, being female or vegetarian can put an athlete at a higher risk for iron deficiency and anemia. Athletes should make sure their diet includes enough iron to support peak performance.

Daily iron supplementation in menstruating people helped improve exercise performance in one study. It has also been shown to improve maximal and submaximal exercise performance in females of reproductive age.

Female athletes of reproductive age are at risk of iron deficiency, Iron supplementation has shown improved athletic performance in this group.

Restless Leg Syndrome

Restless leg syndrome is a health condition in which people have an uncontrollable urge to move their legs. This usually occurs at night and can disrupt sleep.

A systematic review and meta-analysis published in 2019 concluded that iron supplementation is associated with improvement in the International Restless Leg Syndrome score (IRLSS) after four weeks.


Research shows that cognitive levels drop with iron deficiency. In fact, when iron levels in the blood drop, concentration and attentiveness are affected almost immediately. Getting iron levels restored to a normal range can improve concentration and boost cognitive performance.

A double-blind, placebo-controlled study in adolescent girls who were not anemic but had low levels of iron found that iron supplementation improved verbal learning and memory. A total of 81 participants were enrolled in the trial and randomly given either 650 milligrams of oral iron supplementation twice daily or a placebo for eight weeks. Additionally, a review of 26 randomized controlled trials showed that iron supplementation in children with IDA improved hemoglobin levels and reduced deficits in cognitive and motor skills.

Iron: Benefits, Side Effects, Dosage, and Interactions (1)

Iron Deficiency

Iron deficiency is one of the most common nutrient deficiencies. Iron deficiency progresses through phases, ultimately resulting in IDA:

The phases of iron deficiency are as follows:

  1. Storage of iron in the body is depleted, resulting in low serum ferritin levels,
  2. The iron supply available for erythrocyte production is low, but blood hemoglobin levels are still normal,
  3. Iron stores are depleted, resulting in anemia with small RBCs and low blood hemoglobin levels.

What Causes Iron Deficiency?

Iron deficiency results from either excessive losses of iron or too little iron in the diet.

Losses may occur through blood loss, reduced absorption, or prolonged exercise (e.g., athletes who compete in marathon running or cycling endurance events). For example, people who menstruate are at a greater risk of iron deficiency and IDA due to blood loss. And iron deficiency is often more prevalent during pregnancy due to the increased demands of a growing fetus.

People with conditions affecting the gastrointestinal (GI) tract or a history of surgeries on the GI tract are at risk of IDA. For example, those with Crohn's disease or who had a gastric bypass (a type of weight-loss surgery) for obesity may be more likely to be iron deficient. This is because they may not be able to absorb adequate amounts of iron. Iron is absorbed in the duodenum and proximal jejunum (the first part of the small intestine that digested food travels through). Also, stomach surgeries may reduce the production of acid in the stomach which is needed for iron absorption.

Sticking to a vegetarian diet can cause an iron deficiency as plant-based sources of iron do not absorb as well as animal sources.

Groups At Risk of Iron Deficiency

Some people may be more likely to develop an iron deficiency than others.

The risk of developing an iron deficiency is greater in:

  • People who menstruate
  • People who are pregnant
  • Children
  • People who donate blood frequently
  • People who have undergone gastric bypass surgery
  • Premature infants born before 37 weeks of pregnancy
  • Vegetarians and other who lack heme iron (the iron found in meat and seafood) in their diets

The incidence of iron deficiency is almost 25% in people who underwent a Roux-en-Y gastric bypass and about 12% in people who had a gastric sleeve procedure.

Iron deficiency also occurs in many health conditions, such as:

  • Cancer
  • Gastrointestinal disorders (e.g., ulcerative colitis, Crohn's disease)
  • Heart failure
  • Kidney disease while undergoing hemodialysis

Additionally, long-term use of antacids may also put you at a greater risk.

How Do I Know If I Have an Iron Deficiency?

Symptoms of iron deficiency include:

  • Fatigue
  • Shortness of breath
  • Dizziness
  • Headaches
  • Palor (pale skin)
  • Weak and brittle nails
  • Difficulty concentrating
  • Poor memory

If you suspect you have an iron deficiency, you should discuss your symptoms with your healthcare provider. A complete blood count (CBC) will include a hematocrit and hemoglobin level. Low levels of hemoglobin suggest anemia. Your healthcare provider may perform additional tests to determine if an iron deficiency is causing the anemia.

A serum ferritin test is the preferred blood test for diagnosing iron deficiency. It can identify low levels of iron before it progresses to IDA. Generally, a serum ferritin of less than 30 micrograms per liter (mcg/L) suggests iron deficiency, and a level less than 10 micrograms per liter suggests IDA.

The World Health Organization (WHO) recently updated the recommended cut-off values to indicate iron deficiency:

  • Children under the age of 5: Less than 12 micrograms per liter
  • Children 5 years and older and adults: Less than 15 micrograms per liter
  • Children under 5 with infection or inflammation: Less than 30 micrograms per liter
  • Children 5 years and older and adults with infection or inflammation: Less than 70 micrograms per liter

What Are the Side Effects of Iron?

Iron supplements can cause nausea, vomiting, and stomach pain.

Constipation is another very common side effect of iron supplementation. If you are experiencing constipation due to iron supplementation, be sure to get enough fiber and water in your diet. If it continues to be problematic, discuss with your healthcare provider if adding a stool softener is appropriate for you.

The risk of iron overload from diet alone is minimal in most healthy adults. Most of the time, if there is more iron in the body than necessary, the body will save it for future use.

However, people with certain genetic disorders are at risk for iron overload if their conditions cause them to absorb more iron from food.Hemochromatosis is a genetic disorder in which iron builds up in the body. Iron supplementation is not recommended if you have hemochromatosis.

There are very rare cases of iron overdoses leading to internal bleeding, seizure, coma, and even death.

The most common side effect of iron supplementation is stomach upset and constipation. Adequate fiber and water in the diet may help constipation. Discuss with your healthcare provider if adding a stool softener is a good idea.


People with hemochromatosis should avoid iron supplementation. With this condition, iron can build up to dangerous levels in the body.

Keep iron supplements out of reach of children. There are several cases of accidental iron overdoses in children resulting in death. Iron supplements now come with a warning label to make parents aware of this danger.

Dosage: How Much Iron Should I Take?

The recommended dietary allowance (RDA) for iron varies by age and gender:

  • Infants aged 7 to 12 months old; 11 milligrams/day
  • Children aged 1 to 13 years: 7 to 10 milligrams/day
  • Males aged 14 to 18 years: 11 milligrams/day
  • Females aged 14 to 18 years: 15 milligrams/day
  • Male ages 19 and older: 8 milligrams/day
  • Females aged 19 to 50 years: 18 milligrams/day
  • Females aged 51 years and older (or when menopause is reached): 8 milligrams/day

During pregnancy, the requirement increases to 27 milligrams/day. For breastfeeding people, the requirement is 9 to 10 milligrams/day.

The tolerable upper limit (TUL) for iron is:

  • Children under 13 years: 40 milligrams/day
  • Adolescents and adults: 45 milligrams/day

People who are generally healthy and not iron deficient should avoid supplements providing more than the TUL for iron.

For treating iron deficiency, 50 to 100 milligrams/day of iron divided into two to three doses is frequently recommended. Follow a healthcare provider's guidance for iron supplementation for the treatment of a deficiency.

Iron supplements should be taken with food. Some claims suggest that taking iron with vitamin C can help with absorption. However, a recent trial suggests this may not be the case. The trial, which included people with an iron deficiency, found no difference in laboratory indices (hemoglobin and serum ferritin) between those who took iron with vitamin C or iron alone.

Unless you are deficient in iron, you should limit your total iron intake to no more than 45 milligrams daily. Those who are iron deficient should discuss iron supplementation with their healthcare provider.

The 9 Best Iron Supplements of 2023

What Happens if I Take Too Much Iron?

There is minimal risk of developing iron overload from your diet alone.

Taking too much iron from supplements can lead to stomach upset and constipation. Excess iron can cause toxicity, inflammation of the stomach lining, and ulcers. The buildup of iron levels in the body can eventually lead to cirrhosis, liver cancer, and heart disease. Taking iron supplements may also reduce zinc absorption.

In severe cases, iron overdoses (taking 60 mg/kilograms body weight) resulted in organ failure, coma, and death.

It is important to know that iron poisoning can occur in children, potentially causing severe injury or death. Iron poisoning can occur if young children accidentally ingest adult iron capsules or pills. To prevent this, keep supplements out of children's reach and keep them in child-proof containers. Seek medical attention if you think your child may have taken adult iron pills.


Iron supplements may interact with several medications including:

  • Angiotensin-converting enzyme (ACE) inhibitors
  • Carbamazepine, an anticonvulsant drug
  • Levodopa, a medication used to treat Parkinson's disease
  • Levothyroxine, a thyroid medication
  • Penicillamine, a treatment for Wilson's disease and cystinuria
  • Quinolone antibiotics
  • Tetracycline antibiotics

Antacids reduce the acidity in the stomach that is needed for iron absorption. Those taking antacids long-term are at risk of developing iron deficiency.

Certain foods can reduce how well iron is absorbed in the body, including:

  • Black or green teas
  • Coffee
  • eggs
  • Cereal
  • Bread
  • Soy protein

Iron supplements may reduce the absorption of other key micronutrients including zinc, copper, magnesium, and manganese. Calcium may interfere with iron absorption so you should take iron and calcium supplements at different times of the day.

How to Store Iron

It is best to read the labels for how to store iron as there are many different forms of iron in supplements. Keep all iron supplements out of reach of children and pets.

Frequently Asked Questions

  • What is the best way to achieve optimal levels of iron?

    Diet. This minimizes the risk of overdose and ensures you get other important nutrients as well. What you pair iron with also matters. For example, calcium limits absorption. Chemical compounds called tannins, such as those found in tea and coffee, limit absorption too.

  • Is it dangerous to take iron supplements if I am not anemic?

    It can be. Iron supplements are only recommended in cases of diagnosed deficiency or when someone is at high risk for it. Talk to your healthcare provider to confirm the true cause of your symptoms and get advice on proper treatment.

Sources of Iron & What to Look For

Iron is readily available in the diet. Iron in foods comes in two different forms: heme and nonheme. Meat, poultry, and fish provide both heme and nonheme iron, whereas plant-based foods provide only nonheme sources of iron. Heme iron tends to be better absorbed.

Common sources of heme iron in the diet include lean meats and seafood. Oysters, mussels, clams, and sardines are also great sources of iron. Good sources of nonheme iron include beans, lentils, tofu, and leafy green vegetables (e.g., spinach).

In the United States, wheat and some other flours are fortified with iron. Breakfast cereals are also fortified with iron and may be able to meet iron requirements alone.

For infants, breastmilk has enough iron until they reach 6 months of age. After that, the introduction of foods provides additional iron. Infant formulas are often fortified with 12 milligrams per liter of iron.

Additionally, cooking on cast iron can also help you add more iron to your diet.

Iron Supplements

Iron supplements come in many different forms, such as pills, gummies, chews, and liquids. There are also intravenous forms of iron that can be provided under medical supervision.

It is important to note that most iron supplements provide iron as a compound, such as ferrous sulfate, ferrous gluconate, or ferrous succinate. The amount of the compound in the supplement is not the same as the amount of iron in the supplement. For example, ferrous sulfate is only 20% iron. Therefore, 250 milligrams of ferrous sulfate provides 50 milligrams of elemental iron. The supplement facts on the label should indicate the amount of elemental iron so that you don't have to do any calculations.

A medical professional can also give iron intravenously (in the vein). A one-time dose was more effective than oral supplementation for patients who underwent a Roux-en-Y gastric bypass.


Iron is one of the most important minerals your body needs to remain healthy. If left untreated, iron deficiency can progress to anemia. Iron supplements are used to treat iron deficiency and IDA under medical supervision. There is almost no need to supplement iron if you are not iron deficient or anemic.

If you do start iron supplementation on your own, avoid taking more than 45 milligrams daily (the TUL for iron) unless you are treating a deficiency or IDA.

The ideal iron supplement is one that provides the needed dose for you with minimal side effects. It should also be high quality, absorbed well, and a good value for the cost. Talk to your healthcare provider before starting any new supplements.

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