Iron, Fe

Iron is a trace mineral the body needs to build hemoglobin, the oxygen-carrying protein in red blood cells, and myoglobin, which stores oxygen in muscle. Without enough iron, cells throughout the body are starved of the oxygen they need to function, which is why deficiency causes fatigue and impaired concentration long before it becomes visible as anemia.

What Is Iron

Iron exists in food in two chemically distinct forms. Heme iron comes from the hemoglobin and myoglobin in animal tissue — meat, poultry, and seafood — and is absorbed relatively efficiently. Non-heme iron comes from plant foods such as whole grains, nuts, seeds, legumes, and leafy greens, and is absorbed less efficiently on its own. Per Harvard T.H. Chan School of Public Health, The Nutrition Source, pairing non-heme iron with vitamin C or with heme iron at the same meal improves how much non-heme iron the body absorbs, while bran fiber, large amounts of calcium, phytates (found in legumes and grains), and tannins (found in tea) can reduce absorption. In this dataset, concentrated non-heme sources include dried herbs and spices such as thyme, cumin, and turmeric, along with iron-fortified infant cereals, while lentils and iron-fortified breakfast cereals are more realistic everyday contributors at typical serving sizes.

Health Benefits of Iron

Per Harvard's Nutrition Source, iron's central, well-established function is enabling the formation of hemoglobin so blood can transport oxygen from the lungs to the rest of the body; the same source also credits iron with supporting muscle oxygen storage through myoglobin and notes that adequate iron is important for healthy brain development and growth in children.

MedlinePlus adds that iron supports healthy muscle, bone marrow, and organ function, and plays a role in hormone production — benefits that follow directly from iron's role as a component of numerous enzymes and oxygen-carrying proteins throughout the body, rather than a claim of treating any specific condition.

How Much Iron You Need

Established RDA figures (as reported via NIH Office of Dietary Supplements, Iron — Health Professional Fact Sheet; this fact sheet blocked direct automated fetch and its core figures were corroborated by Harvard's Nutrition Source, which independently reports the same values) include: adult men 19–50 years, 8 mg/day; adult women 19–50 years, 18 mg/day (reflecting menstrual iron losses); and pregnancy, 27 mg/day. Needs are generally lower after menopause, converging toward the male adult figure.

The Tolerable Upper Intake Level (UL) for iron is 45 mg/day for adults ages 14 and older, per the same corroborated sourcing. This UL applies to iron from food and supplements combined and does not apply to iron given under medical supervision for treating deficiency.

Signs of Deficiency and Excess

Iron deficiency progresses in stages. MedlinePlus notes that early iron deficiency may cause no noticeable symptoms, but as it progresses to iron-deficiency anemia it causes tiredness, shortness of breath, and difficulty concentrating or remembering. Harvard's Nutrition Source adds that people who are iron deficient are less able to fight infections, exercise, and regulate their body temperature.

Excess iron is a different concern. Taking high-dose iron supplements, especially on an empty stomach, commonly causes stomach upset, nausea, constipation, and abdominal pain, per MedlinePlus. At extremely high doses — hundreds to thousands of milligrams, generally from accidental overdose rather than normal diet or standard supplementation — iron can cause organ failure, coma, convulsions, and death. Separately, a subset of people have hereditary hemochromatosis, a genetic condition in which the body absorbs too much iron regardless of intake; over time this can damage the liver, heart, and pancreas, and can progress to liver cirrhosis, liver cancer, or heart disease if untreated.

Warnings & Interactions

People with hereditary hemochromatosis or other iron-overload conditions should avoid iron supplements (and, per MedlinePlus, vitamin C supplements, which increase iron absorption) unless a clinician directs otherwise, since their bodies already retain excess iron.

Iron supplements can interfere with certain medications. MedlinePlus notes that iron can reduce how much levodopa — used to treat Parkinson's disease and restless leg syndrome, found in drugs such as Sinemet and Stalevo — the body absorbs, making the medication less effective; iron supplements are generally advised to be taken several hours apart from levodopa and from certain antibiotics for the same reason.

Beyond the 45 mg/day UL described above, there is no documented benefit to iron intake beyond what corrects or prevents deficiency; taking iron supplements without a diagnosed need or medical reason is not supported by the sourcing reviewed here and carries the gastrointestinal and, at high doses, more serious risks described above.

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