Iron Deficiency Anemia: Who Is at Risk, and What Actually Helps

Iron deficiency anemia is the most common nutritional deficiency in the world. The World Health Organization estimates that roughly 30 percent of women of reproductive age and 40 percent of pregnant women are anemic, with iron deficiency responsible for at least half of those cases. In wealthier countries the numbers are lower but not trivial: the CDC reports that around 10 percent of teenage girls and women aged 12 to 49 are iron deficient. The condition is easy to miss because the symptoms, fatigue, brain fog, shortness of breath with exertion, and pale skin, are nonspecific and develop slowly. This guide covers who is at risk, what to eat, what tests to ask for, and how to supplement safely.

Why iron matters

Iron has two main jobs in the body. Most of it, about 70 percent, sits in hemoglobin inside red blood cells, where it carries oxygen from the lungs to tissues. Another 25 percent is stored as ferritin and hemosiderin, mostly in the liver, spleen, and bone marrow. The remaining 5 percent works in myoglobin (which stores oxygen in muscle), in cytochromes that power the electron transport chain, and in enzymes that synthesize DNA and neurotransmitters.

The body is remarkably stingy with iron. We absorb only what we need, and we lose very little. Men lose about 1 mg per day through skin cells, sweat, and minor gastrointestinal bleeding. Menstruating women lose an additional 0.5 mg per day on average. Because absorption is only 10 to 18 percent of intake from a typical Western diet, the RDA works out to 8 mg per day for men and 18 mg per day for premenopausal women. Pregnant women need 27 mg per day.

Who is most at risk?

Menstruating women

Heavy menstrual bleeding is the single most common cause of iron deficiency in women of reproductive age. The American College of Obstetricians and Gynecologists defines heavy bleeding as more than 80 mL per cycle, but in practice the diagnosis is clinical. If you are soaking through pads or tampons every two hours, passing clots larger than a quarter, or bleeding for more than seven days, your iron losses are likely substantial. Teenage girls are at particularly high risk because rapid growth and menstruation coincide.

Pregnant women

Pregnancy roughly triples iron requirements. The fetus takes iron, the placenta takes iron, and maternal blood volume expands by 40 to 50 percent. The CDC and the American College of Obstetricians and Gynecologists recommend universal low-dose iron supplementation (27 mg per day, the amount in most prenatal vitamins) during pregnancy. The WHO recommends 30 to 60 mg per day for pregnant women in regions where anemia prevalence exceeds 20 percent.

Infants and young children

Rapid growth demands iron. Exclusively breastfed infants are at particular risk after about 4 to 6 months, because breast milk is low in iron. The American Academy of Pediatrics recommends iron-fortified formula for formula-fed infants and iron supplements for exclusively breastfed infants starting at 4 months until iron-rich complementary foods are introduced.

Vegetarians and vegans

Plant iron (non-heme) is absorbed at about one-third the rate of animal iron (heme). The Institute of Medicine set the RDA for vegetarians at 1.8 times the standard RDA, which works out to 14 mg per day for vegetarian men and 32 mg per day for vegetarian premenopausal women. With careful planning this is achievable, but it requires intentional inclusion of legumes, fortified grains, and leafy greens.

People with GI blood loss or malabsorption

Ulcers, colorectal cancer, inflammatory bowel disease, hiatal hernia, and chronic NSAID use can all cause slow GI bleeding. Celiac disease and Helicobacter pylori infection impair absorption. Endurance athletes, especially distance runners, lose small amounts of iron through foot-strike hemolysis (red blood cells destroyed in the feet during running) and GI bleeding triggered by intense exercise.

People who donate blood regularly

Each whole blood donation removes about 200 to 250 mg of iron. Frequent donors, particularly women who are already menstruating, can become iron depleted. The American Red Cross recommends iron supplementation for frequent donors, a recommendation supported by a randomized trial published in JAMA in 2017 by Kiss and colleagues.

Heme versus non-heme iron

Iron in food comes in two forms. Heme iron, found only in animal flesh (meat, poultry, fish), is absorbed at 15 to 35 percent. Non-heme iron, found in plants, dairy, eggs, and supplements, is absorbed at 2 to 20 percent. The difference matters because most of the iron in a typical Western diet is non-heme, and the same meal can dramatically shift how much of it you actually absorb.

Heme iron sources (per 3-ounce serving)

• Beef liver: 5 mg
• Oysters: 8 mg (varies by type)
• Beef (chuck, lean): 3 mg
• Dark meat chicken: 1 mg
• Light meat chicken: 0.5 mg
• Tuna (canned light): 1 mg

Non-heme iron sources (per serving)

• Fortified breakfast cereal: 8 to 18 mg (varies)
• Lentils, cooked: 6.6 mg per cup
• Spinach, cooked: 6.4 mg per cup
• Tofu, firm: 3 mg per half cup
• White beans, cooked: 8 mg per cup
• Pumpkin seeds: 4 mg per ounce
• Dark chocolate (70 to 85 percent): 7 mg per ounce

Estimate your intake with the Iron Calculator.

How to actually absorb the iron you eat

Pair iron with vitamin C

Vitamin C reduces non-heme iron to a more absorbable form and binds it in a soluble complex. Adding 50 to 100 mg of vitamin C to a plant-based meal can increase non-heme iron absorption three- to fourfold. A bell pepper, a kiwi, half a cup of strawberries, or a small glass of citrus juice with your lentils or fortified cereal does the job. This is one of the most practical, evidence-based tricks for vegetarians.

Separate iron from calcium, coffee, and tea

Calcium inhibits both heme and non-heme iron absorption. A glass of milk with an iron-rich meal can cut absorption by half. Polyphenols in coffee and black tea (including iced tea and green tea) bind non-heme iron and reduce absorption by 60 to 90 percent. Phytates in whole grains and legumes also inhibit absorption. The practical advice: take your iron-rich meal or supplement away from coffee, tea, dairy, and calcium supplements by at least an hour, ideally two.

Use a cast-iron skillet

This sounds like folk wisdom, but it has been measured. Cooking acidic foods like tomato sauce in a cast-iron skillet significantly increases their iron content. A 1986 study in the Journal of the American Dietetic Association found that the iron content of spaghetti sauce increased from 0.6 mg to 5.7 mg per serving after cooking in cast iron.

Combine legumes with meat or fish

The so-called meat factor, an unidentified component of muscle tissue, enhances non-heme iron absorption from plant foods eaten at the same meal. Adding a small amount of meat or fish to a bean dish meaningfully improves absorption of the bean iron. This is partly why traditional combinations like rice and beans with a small amount of meat work well nutritionally.

Testing: serum ferritin is the key test

The standard panel for iron status includes hemoglobin, hematocrit, serum ferritin, transferrin saturation, and sometimes serum iron and total iron binding capacity (TIBC). Of these, ferritin is the most useful early marker, because it reflects iron stores and drops before hemoglobin does.

The catch: ferritin is an acute phase reactant, meaning it rises with inflammation, infection, liver disease, and alcohol intake. A ferritin of 50 ng/mL in a healthy person usually reflects decent iron stores, but the same value during an infection or with active inflammation can mask true deficiency. Inflammatory markers like CRP should be checked at the same time, and a ferritin below 30 ng/mL in an otherwise healthy adult is generally diagnostic of iron deficiency regardless of hemoglobin.

Hemoglobin is what defines anemia. The WHO defines anemia as hemoglobin below 13 g/dL in men, below 12 g/dL in non-pregnant women, and below 11 g/dL in pregnant women. But you can be iron deficient without being anemic. Iron deficiency without anemia still causes symptoms and should be treated. The Ferritin Interpreter and CBC Interpreter can help you read your own results.

Supplementation: form, dose, and side effects

Iron supplements come in several forms. Ferrous sulfate, ferrous gluconate, and ferrous fumarate are the cheapest and best studied. Each contains a different percentage of elemental iron: ferrous sulfate is 20 percent elemental iron, ferrous gluconate is 12 percent, and ferrous fumarate is 33 percent. A typical 325 mg ferrous sulfate tablet contains 65 mg of elemental iron.

The standard adult dose for treating iron deficiency anemia is 60 to 200 mg of elemental iron per day, often divided. Recent trial evidence suggests that alternate-day dosing may improve absorption and reduce side effects. A 2020 randomized trial by Stoffel and colleagues in JAMA found that giving iron on alternate days rather than daily increased fractional absorption by about 34 percent and reduced hepcidin-mediated absorption block. The practical implication: you may not need to take iron every day, and you may tolerate it better if you do not.

Common side effects include constipation, nausea, abdominal pain, and dark stools. Taking iron with food reduces side effects but also reduces absorption, so the trade-off depends on what you can tolerate. Extended-release formulations and polysaccharide iron complex are gentler on the gut but more expensive.

Iron overdose is dangerous, particularly in children. The FDA requires iron supplements to be packaged in child-resistant containers and warns that as little as 200 mg of elemental iron can be fatal in a young child. Keep iron supplements away from children.

How long does repletion take?

Hemoglobin typically starts to rise within 2 to 3 weeks of starting iron therapy and reaches normal in about 2 months. Ferritin takes much longer, often 3 to 6 months, because the body prioritizes making red blood cells before rebuilding stores. The standard advice is to continue iron for 3 to 6 months after hemoglobin normalizes to rebuild ferritin. Retest ferritin at 3 months to confirm the trend.

If iron stores do not improve despite supplementation, the most common reasons are ongoing blood loss (often GI), malabsorption (celiac disease, H. pylori, autoimmune gastritis), non-adherence, or taking iron with inhibitors. A failure to respond to oral iron is a reason to look harder, often starting with a GI workup.

Special populations

Endurance athletes

Distance runners, especially women, are at risk due to foot-strike hemolysis, sweat losses, and exercise-induced GI bleeding. The American College of Sports Medicine recommends periodic ferritin screening in endurance athletes and supplementation when ferritin falls below 30 ng/mL, even without anemia.

People with chronic kidney disease

CKD patients often need intravenous iron because oral absorption is impaired by chronic inflammation and elevated hepcidin. This is a clinical decision and not something to manage on your own.

Blood donors

The American Red Cross suggests that frequent donors take 18 to 38 mg of elemental iron per day for 60 days after each whole blood donation to restore stores.

The bottom line

Iron deficiency is common, especially in menstruating women, pregnant women, infants, vegetarians, and endurance athletes. The symptoms are easy to miss. Ask for ferritin, not just hemoglobin, if you are at risk or symptomatic. Treat with food first: combine plant iron with vitamin C, separate it from coffee, tea, and dairy, and use cast iron for acidic dishes. If you need a supplement, ferrous sulfate is cheap and effective, alternate-day dosing may improve tolerance, and repletion takes months, not weeks. If iron stores do not improve, look for blood loss or malabsorption rather than just increasing the dose.