iron

Iron is an essential mineral the body needs for growth and development. The NIH Office of Dietary Supplements explains that the body uses iron to make hemoglobin (the red-blood-cell protein that carries oxygen from the lungs to the rest of the body) and myoglobin (which delivers oxygen to muscles), and that iron is also needed to make some hormones. In supplements it is commonly supplied as a ferrous or ferric iron salt, such as ferrous sulfate, ferrous gluconate, ferric citrate, or ferric sulfate.

According to the NIH, iron is an essential nutrient, and supplements or iron-fortified foods can help groups with higher needs, such as infants, young children, and people who are pregnant, avoid iron deficiency. The evidence is strongest for correcting a diagnosed deficiency or iron-deficiency anemia. Most people in the United States get enough iron from food, and the NIH notes that healthy people who already meet their needs generally do not need a supplement. Taking iron without a demonstrated need is not supported by the evidence and can be harmful.

Recommended intakes vary by age, sex, and life stage. The NIH lists about 8 mg/day for adult men, 18 mg/day for women age 19 to 50, and 27 mg/day during pregnancy; people who follow vegetarian diets are advised to aim for almost twice the listed amount because nonheme plant iron is absorbed less efficiently. The Tolerable Upper Intake Level from all sources is 45 mg/day for everyone age 14 and older (40 mg/day for children 13 and younger), though a clinician may prescribe more for a limited time to treat a deficiency. Because iron should be taken only when there is a genuine need and the right dose depends on your iron status, talk to a clinician and get tested before starting an iron supplement.

Iron can be harmful in excess. The NIH warns that accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6, so iron supplements must be kept out of children's reach. Extremely high doses (in the hundreds to thousands of mg) can cause organ failure, convulsions, coma, and death. People with hemochromatosis or other iron-overload conditions should avoid iron supplements unless a doctor directs otherwise, and no one should exceed the 45 mg/day upper limit without medical supervision.

In healthy people, high doses of iron supplements—particularly on an empty stomach—can cause an upset stomach, constipation, nausea, abdominal pain, vomiting, and diarrhea. The NIH notes that larger amounts may lead to more serious effects, including inflammation of the stomach lining and ulcers, and can also reduce zinc absorption.

Iron can interfere with several medications. The NIH notes that iron supplements can reduce the absorption and effectiveness of levodopa (used for Parkinson's disease and restless legs) and of levothyroxine (a thyroid medication). Proton pump inhibitors such as omeprazole and lansoprazole lower stomach acid and may reduce how much nonheme iron the body absorbs from food, and calcium may also interfere with iron absorption, so taking calcium and iron at different times of day may help. Because spacing matters for some of these drugs (levothyroxine labels, for example, commonly advise separating doses from iron), tell your doctor and pharmacist about all supplements and medicines you take.