Iron: Overview, Supplement Side Effects, and More
Key takeaways:
Symptoms of low iron levels (iron deficiency) can improve with iron supplements and a diet rich in iron.
Animal sources of iron (heme iron) are easier to absorb than plant-based sources (non-heme iron). If you do not eat meat or fish products, you’ll need about twice as much iron as is normally recommended.
For people with normal iron levels, iron supplements likely won’t help with memory, exercise performance, or fatigue.
Table of contents
What is iron?
Iron is an essential mineral found in plants and proteins. Our bodies need iron to make hemoglobin. Hemoglobin is the part of red blood cells that helps carry and deliver oxygen around the body.
Iron: Sources and supplements
Iron from food comes in two forms: heme and non-heme.
Heme iron is absorbed better by the body than non-heme iron. You can get heme iron only from eating meat and fish.
Non-heme iron is not absorbed as well by the body. You need to eat more of it to get the same amount. You can get non-heme iron from plant foods and in meat and fish, too, since animals consume plant foods.
Most people who eat a healthy and balanced diet get enough iron from their food and do not need supplements. You will absorb more iron if you eat it with foods rich in vitamin C, such as citrus fruits, strawberries, sweet peppers, and tomatoes.
Natural sources of iron include:
Meat, fish, and seafood
Vegetables like dark, leafy greens (spinach), lentils, beans, peas, and potatoes
Nuts, seeds, and some dried fruits
Grains and cereals enriched with iron
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Most multivitamins contain iron. Iron is also found in supplements like:
Ferrous sulfate
Ferrous gluconate
Ferric citrate
Ferric sulfate
Iron supplement dosing
Here’s how much iron people need per day (the recommended daily allowance, or RDA). It varies based on a person’s sex, age, and situation:
11 mg for non-menstruating teens, 18 mg for menstruating teens
8 mg for non-menstruating adults
15 to 18 mg for menstruating adults
27 mg for pregnant adults
9 to 10 mg for lactating adults
Unless you are prescribed more by your provider, teens and adults should not take more than 45 mg of iron per day from all sources (or 40 mg for infants and children).
Common uses for iron supplements
If you have an iron deficiency, an iron-rich diet will not be enough to improve your iron levels. This is where iron supplements come in.
Iron supplements work to treat:
Low iron levels
Anemia caused by low iron levels
Symptoms caused by low iron levels or iron-deficiency anemia
Iron supplements for people with normal iron levels do not help with:
Exercise performance
Concentration
Mental alertness
Fatigue
Any other symptoms
The science behind iron supplements
People with normal iron levels should not take iron supplements. There’s no evidence that taking iron supplements with normal iron levels will have any purported benefits (like those mentioned above).
Treating iron deficiency with iron supplements — whether you have anemia or not — can help improve symptoms of iron deficiency or iron-deficiency anemia. These symptoms may include:
Weakness
Headache
Low exercise tolerance
Fatigue
Irritability
Iron supplement interactions
Iron supplements can cause these medications to not work as well:
Levothyroxine (Synthroid)
Levodopa, found in Sinemet (carbidopa/levodopa)
Tetracycline antibiotics, like doxycycline (Vibramycin)
Penicillamine (Depen)
Ciprofloxacin (Cipro)
Some medications, supplements, and foods can prevent iron from being absorbed. It’s important to know this, since these interactions can impact iron levels. They can lead to iron deficiency or iron supplements not working well.
These medications and foods can prevent iron from being absorbed:
Proton pump inhibitors, like omeprazole (Prilosec) and lansoprazole (Prevacid)
Foods and drinks high in calcium, like milk
High-fiber foods like whole grains
Foods or drinks with caffeine, like coffee and tea
You should take your iron supplements at least 2 hours before or after any of these medications or foods.
Side effects of iron supplements
Serious side effects from iron supplements are rare. For most people, it’s not common to absorb too much iron. When the body recognizes that it has enough iron, it will absorb less from your supplements.
Common side effects of iron supplements include:
Upset stomach and cramps
Tips and tricks for avoiding side effects include:
For nausea:
Take with a little food: Iron is best absorbed on an empty stomach. But if you are getting nausea with your supplement, try taking it with a little food.
Take in smaller doses: Some people get more severe nausea and vomiting with higher doses of iron. It can help to take smaller doses throughout the day.
For teeth staining:
Mix liquids with water: Liquid formulations may stain your teeth. Mixing the liquid with water and drinking it with a straw may help prevent stains.
Use baking soda: If your teeth do become stained, you can brush your teeth with baking soda to remove them.
Know that iron supplements can make your stools look black. This is normal. But if your stool has blood in it, or you’re having stomach cramps, talk to your healthcare provider.
Safety of iron supplements
Most people with iron deficiency can safely take iron supplements.
Iron supplements may not be safe for the following people:
People who don’t have an iron deficiency: Taking high amounts of iron supplements when you have normal iron levels can cause side effects.
People with hemochromatosis: People with hemochromatosis (iron overload) should avoid iron and vitamin C supplements.
Children: The dose of iron in adult supplements is much too high for children. Iron poisoning can easily happen in children if they accidentally ingest adult doses of iron.
High doses of iron can cause complications such as:
Lowering the amount of zinc absorbed in the body
Very high doses of iron (hundreds or thousands of mg) can cause severe poisoning and even death
All multivitamins and iron supplements should be kept out of reach of children.
FAQs
No. Folic acid and iron are not the same. Folic acid is a B vitamin also known as B9. It comes from plants, where it’s called folate, and is in fortified foods (as folic acid).
Like iron, our body needs folic acid to make red blood cells. But both have different roles in making and maintaining healthy red blood cells.
Low levels of folic acid and iron can both cause anemia, but these are different types of anemia with different treatments.
It’s best not to. Here’s why:
Iron doses of greater than 25 mg may lower the amount of zinc that your body can absorb. But it’s not clear if this effect is significant enough to make it worrisome.
Taking zinc may lower iron levels.
It depends on what you’re treating:
Iron supplements are better for treating low iron levels and anemia.
Zinc is better for treating low zinc levels.
When it comes to healthy eating, both iron and zinc are important minerals that the body needs and cannot make by itself. Luckily, the nutrients share some common sources, like red meat, poultry, seafood (oysters, crab, lobster), beans, and nuts.
Disclaimer: The FDA does not test supplements for safety and effectiveness. Supplements can contain harmful substances. They can also affect how your medications work. Always speak with your healthcare provider before taking any supplement.
Why trust our experts?
References
American Society of Hematology. (n.d.). Iron-deficiency anemia.
Campbell, N. R. C., et al. (1991). Iron supplements: A common cause of drug interactions. British Journal of Clinical Pharmacology.
de Oliveira, K. D. J. F., et al. (2009). Effect of zinc supplementation on the antioxidant, copper, and iron status of physically active adolescents. Cell Biochemistry & Function.
MedlinePlus. (2021). Taking iron supplements.
Mekonnen, S. (n.d.). Iron poisoning. National Capital Poison Center.
Mount Sinai. (n.d.). Zinc.
National Heart, Lung, and Blood Institute. (n.d.). Iron-deficiency anemia.
National Institutes of Health. (2021). Folate fact sheet for health professionals.
National Institutes of Health. (2021). Iron fact sheet for consumers.
The Nutrition Source. (n.d.). Iron. Harvard T.H. Chan School of Public Health.
U.S. Food and Drug Administration. (2022). What you need to know about dietary supplements.
Walker, C. F., et al. (2005). Interactive effects of iron and zinc on biochemical and functional outcomes in supplementation trials. The American Journal of Clinical Nutrition.
Whittaker, P. (1998). Iron and zinc interactions in humans. The American Journal of Clinical Nutrition.
