Iron is a bit of a paradox. Iron deficiency is the most common nutrient deficiency in the world, and it leaves millions of people tired, pale and short of breath. Yet iron is also one of the few supplements that can do real harm when taken without a reason. That is why iron, more than almost any other supplement, is worth discussing with your doctor before you start.
What iron does
Iron is a key part of hemoglobin, the protein in red blood cells that carries oxygen from your lungs to the rest of your body. When you run low, your body makes fewer and smaller red blood cells. That is iron deficiency anemia. Before anemia shows up, your iron stores can drop for months, and some people feel tired even at that stage.
How much you need
The U.S. Office of Dietary Supplements lists these daily amounts on its iron fact sheet:
- Men 19 and older: 8 mg
- Women 19 to 50: 18 mg
- Women 51 and older: 8 mg
- During pregnancy: 27 mg
- Upper limit for adults: 45 mg a day from supplements, unless your doctor prescribes more
Vegetarians and vegans may need about 1.8 times more, because iron from plants is absorbed less well.
Who is most at risk
- Women with heavy periods. This is the most common cause of iron deficiency in adults.
- Pregnant women. Blood volume rises sharply, and so does iron need. Most prenatal vitamins include iron. See our prenatal vitamins guide.
- Babies, toddlers and teenagers, who are growing fast. Teen girls are especially at risk once periods begin. See do kids need supplements.
- Frequent blood donors.
- People with digestive conditions, such as celiac disease or inflammatory bowel disease, or after weight-loss surgery.
- People taking acid-reducing medicines long term. Stomach acid helps you absorb iron. See antacids, kidneys and bone health.
- Endurance athletes, especially women and runners.
Signs you might be low
Common signs include fatigue, weakness, pale skin, shortness of breath when climbing stairs, headaches, cold hands and feet, brittle nails, and a strange craving to chew ice. Many of these overlap with other conditions, which is why a blood test matters.
The tests that matter
A complete blood count shows whether you are anemic. Ferritin shows your iron stores, and it often drops well before anemia appears. Your doctor may also check iron, transferrin saturation and other markers. Ferritin can read falsely normal or high when you have inflammation or an infection, so your doctor will interpret it in context.
One important point for men and for women after menopause: iron deficiency in these groups is not something to just treat with a pill. It can be a sign of slow blood loss from the gut, such as an ulcer or a colon polyp, and your doctor will want to find the cause.
Why you should not take iron "just in case"
Your body has no good way to get rid of extra iron. It holds on to it. Over time, too much iron can build up in organs. Some people inherit a condition called hemochromatosis, which makes them absorb too much iron, and supplements make it worse.
Iron is also a serious poisoning risk for young children. Accidental overdose of iron pills has historically been a leading cause of poisoning deaths in children under 6, which is why iron products carry a warning label in the United States. Keep iron, including prenatal vitamins and adult multivitamins, locked away and out of reach. Our post on how to store supplements has practical tips.
Getting more iron from food
There are two kinds of iron in food:
- Heme iron, in red meat, poultry and seafood, is absorbed best.
- Non-heme iron, in beans, lentils, tofu, spinach, fortified cereals and pumpkin seeds, is absorbed less well, but you can boost it.
To absorb more plant iron, pair it with vitamin C. Beans with salsa, cereal with strawberries, or lentil soup with tomatoes all work. Tea, coffee and calcium can block iron absorption, so have them between meals rather than with your iron-rich food. Cooking in a cast iron pan can add a little iron, too.
How to take an iron supplement well
If your doctor recommends iron:
- Take it on an empty stomach if you can, with water or orange juice. If it upsets your stomach, take it with a small amount of food.
- Keep it apart from calcium, antacids, tea, coffee and dairy by about two hours.
- Ask about every-other-day dosing. Some studies suggest the body absorbs iron better when it is taken every other day, and it may cause fewer stomach problems. Ask your doctor whether this suits you.
- Expect dark stools. That is normal. Constipation and nausea are common, and a lower dose or a different form can help.
- Keep it away from certain medicines. Iron can reduce absorption of thyroid medicine, some antibiotics and a few other drugs. See supplement and drug interactions.
- Get rechecked. It often takes a few months to rebuild your stores. Your doctor will usually repeat blood tests.
Forms like ferrous sulfate, ferrous gluconate and ferrous fumarate all work. Ferrous sulfate is cheap and well studied. Some people tolerate other forms better. Check the label for elemental iron, which is the amount your body can actually use. See how to read a supplement label.
The bottom line
Iron supplements are a real help for people who are deficient, and a potential harm for people who are not. If you feel tired and suspect low iron, ask for a blood test, including ferritin, before you start. Keep iron away from children. For more, see our iron ingredient page and the minerals category.