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Iron-Deficiency Anemia

The most common nutritional deficiency worldwide. Reduced hemoglobin causes fatigue, brain fog, breathlessness and cold intolerance. Often a sign of blood loss (menstrual or gastrointestinal) or poor absorption (such as celiac disease or H. pylori), not just inadequate intake.

Kidney & Blood Evidence-Based

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Definition

What Is Iron-Deficiency Anemia?

Iron-deficiency anemia (IDA) is reduced red blood cell mass and hemoglobin due to insufficient iron stores. Iron is essential for hemoglobin synthesis; without adequate iron, the body cannot produce enough functional red blood cells, leading to inadequate oxygen delivery throughout the body. It is the most common nutritional deficiency worldwide.

Iron deficiency progresses through stages: depleted iron stores (low ferritin, normal hemoglobin) โ†’ iron-deficient erythropoiesis (low ferritin and low transferrin saturation, hemoglobin still normal) โ†’ frank anemia (low hemoglobin). Symptoms can develop at any stage; low ferritin alone causes significant symptoms even before anemia develops.

Key point: iron-deficiency anemia is a sign, not just a diagnosis. The question is always why. Common causes include menstruation (women), GI bleeding (men and postmenopausal women, must rule out cancer), inadequate intake (vegetarians/​vegans), malabsorption (celiac, hypochlorhydria, H. pylori, PPIs, gastric bypass) and chronic disease. Giving iron supplements without addressing the cause is incomplete care.

โš ๏ธ Always Investigate Cause: Iron-deficiency anemia in adult men, postmenopausal women or patients with risk factors requires GI evaluation (upper endoscopy + colonoscopy) to rule out occult malignancy. Don't just supplement; find and treat the cause. Premenopausal women: menstrual loss is usually the cause, but evaluate if heavy bleeding or other risk factors.
A tired woman with pale skin, three small faces for pale skin, headache and shortness of breath, a close-up of fewer red blood cells, and a normal red cell beside a pale anemic one

Three Ways Iron Runs Low

Blood Loss

Menstruation (heavy or normal over years), occult GI bleeding (ulcers, cancer, polyps, hemorrhoids), frequent blood donation, hemorrhagic conditions.

Malabsorption

Celiac disease, H. pylori gastritis, hypochlorhydria (low stomach acid), PPIs, autoimmune gastritis, gastric bypass, inflammatory bowel disease.

Inadequate Intake

Vegetarians/​vegans (plant iron less bioavailable), restrictive diets, pregnancy/​lactation (increased needs), infants and toddlers (high needs).

By the Numbers

Iron-Deficiency Anemia by the Numbers

~30%
of women of reproductive age worldwide have anemia, with iron deficiency the leading cause1
~9%
of nonpregnant US women aged 20 to 45 had iron-deficiency anemia in 2021 to 2023, up from about 4% in 1999 to 2000 2
2 to 5%
of adult men and postmenopausal women in high-income countries have IDA, which always needs a GI workup133
36.5%
of pregnant women worldwide have anemia, most commonly from iron deficiency1
~1 in 3
men and postmenopausal women with iron-deficiency anemia have an underlying disease, most often in the gut13
3 to 5%
of people with iron-deficiency anemia turn out to have celiac disease, so it is screened for routinely13
Signs & Symptoms

Symptoms of Iron-Deficiency Anemia

Many people are surprised that low ferritin without anemia can cause significant symptoms. Iron is needed for energy production, cognition, thyroid function and more.

SymptomWhat happens
Energy & Cognitive
Profound FatigueDisproportionate to activity. Often the dominant symptom. May develop gradually so patients don't notice. Usually improves with iron repletion.
Brain Fog & Poor ConcentrationDifficulty concentrating, poor memory, "fuzzy thinking." Iron is essential for neurotransmitter synthesis. Impacts work performance, learning.
Shortness of Breath / Exercise IntoleranceWith exertion (climbing stairs, walking). Worse than expected for fitness level. Reduced oxygen delivery to tissues.
Rapid Heart Rate / PalpitationsCompensatory tachycardia. Heart pumps faster to compensate for reduced oxygen-carrying capacity. May feel like "racing heart" at rest.
Specific Iron Deficiency Signs
Restless Legs SyndromeStrong urge to move legs, especially at night. Highly responsive to iron repletion. Always check iron status in RLS patients (iron is offered when ferritin is 75 ng/mL or below).6
Pica (Ice / Unusual Cravings)Compulsive ice eating (pagophagia) is characteristic. Also dirt, clay, paper, raw starch. Strongly associated with iron deficiency. Usually resolves with treatment.
Nail & Hair ChangesSpoon-shaped nails (koilonychia), brittle nails, hair thinning/loss. Hair loss may be diffuse. May be sole presenting symptom.
Pale Skin, Mucous Membranes, Cracked LipsPallor (especially inside lower eyelids, palms). Angular cheilitis (cracking at corners of mouth). Glossitis (smooth, sore tongue). Cold hands and feet.
Causes

Causes of Iron-Deficiency Anemia

Iron-deficiency anemia develops when the body loses more iron, or needs more, than it absorbs. It is often caused by more than one thing at once, and a cause should be looked for in everyone13.

CauseHow It Contributes to Iron-Deficiency AnemiaWhat Helps
Menstrual blood lossPeriods are a major contributor in young women, alongside pregnancy and low intake13A clinician's assessment of heavy periods, iron repletion and plant iron paired with vitamin C
Bleeding in the gutUlcers, polyps and cancers can bleed slowly without specific symptoms; about a third of men and postmenopausal women with iron-deficiency anemia have an underlying disease, most often in the gut13Upper endoscopy and colonoscopy to find and treat the source
Poor absorptionCeliac disease, H. pylori infection, atrophic gastritis, gastric surgery or bypass, and long-term use of a proton pump inhibitor all reduce how much iron is absorbed13Celiac screening, H. pylori testing and treatment, a review of acid-suppressing medicine with the prescriber, and intravenous iron when tablets cannot be absorbed
Low dietary intakePoor dietary intake is a recognized cause on its own and often adds to another one13Heme iron foods and plant iron paired with vitamin C, with tea, coffee and calcium kept apart from iron-rich meals
PregnancyPregnancy raises iron needs and is one of the major contributors to iron deficiency in young women13Iron checks in prenatal care, with extra iron when a deficiency is found
Blood donation and regular NSAID useFrequent blood donation and long-term NSAID use are recognized risk factors a clinician should ask about13Telling your clinician about donations and regular NSAID use, so iron can be checked and alternatives considered
Diagnosis

How Iron-Deficiency Anemia Is Diagnosed

TestWhat it shows
Iron Studies
Ferritin (Most Specific)Reflects iron stores. <30 ng/mL = iron deficiency; <15 to 20 = definitive. Target for repletion: >50 ng/mL (or >75 for symptoms). Caution: falsely elevated in inflammation.5
CBC (Complete Blood Count)Microcytic (low MCV), hypochromic (low MCH) anemia. RDW elevated (variable size). Mild anemia: hemoglobin 10 to 12 g/dL; moderate: 8 to 10 g/dL; severe: below 8 g/dL.
Iron, TIBC, Transferrin SaturationSerum iron low, TIBC high, transferrin saturation <20% in IDA. Less reliable than ferritin. Levels vary throughout the day.
Reticulocyte CountLow in iron deficiency. Distinguishes from hemolysis. Rises rapidly after iron repletion (sign treatment is working).
Cause Investigation
Upper Endoscopy + ColonoscopyRequired in adult men, postmenopausal women, premenopausal women with risk factors. Rules out occult GI malignancy, ulcers, celiac.
Celiac Disease ScreenTissue transglutaminase IgA + total IgA. Celiac disease is found in 3 to 5% of people with iron-deficiency anemia. It should be screened for in all unexplained IDA.7
H. pylori TestingCauses occult bleeding and reduced iron absorption. Stool antigen, urea breath, biopsy testing. Treat if positive.
Menstrual History (Women)Heavy menstrual bleeding (HMB) screen, >80 mL blood loss/cycle. Common but underdiagnosed cause. May need gynecology evaluation.
Treatment Comparison

Conventional and Holistic Treatment for Iron-Deficiency Anemia

๐ŸŒฟ HOLISTIC
๐Ÿ’Š CONVENTIONAL
๐ŸŒฟ

Holistic / Functional Approach

Address the cause while supplementing. Often gut function (absorption) matters more than intake.

Finding the Cause
Find why (bleeding, malabsorption or low intake) and treat it
Absorption Optimization
Address H. pylori, treat celiac, pair iron with vitamin C, away from coffee/tea/calcium
Form Matters
Heme iron from food best absorbed. Iron bisglycinate causes fewer side effects than ferrous sulfate.
Monitoring
Check hemoglobin within the first 4 weeks of iron treatment, and continue the iron for about 3 months after hemoglobin normalizes to refill iron stores.10

Full Holistic Approach Includes

  • Identify and treat the underlying cause: heavy menses (gyn workup, hormone management), GI bleeding (endoscopy/​colonoscopy), malabsorption (celiac testing, H. pylori, address hypochlorhydria)
  • Cooking in cast iron: adds iron to food (especially acidic foods like tomato sauce)
  • Iron bisglycinate: chelated form, fewer GI side effects, possibly better absorbed than ferrous sulfate. 25 to 50 mg elemental iron daily. The top of this range is above the 45 mg/day upper intake level; take it only to correct a confirmed deficiency, at a dose your clinician sets.
  • Alternate-day dosing: emerging evidence that it improves absorption (less hepcidin block) and reduces side effects
  • Avoid these with iron: coffee, tea, calcium supplements, dairy, antacids, calcium-rich foods (separate by 2+ hours)
  • If low stomach acid is suspected (for example autoimmune gastritis), ask for it to be investigated; acid supplements are not proven to improve iron absorption
  • Treat H. pylori if positive; it is a recognized cause of poor iron absorption13
  • Ask about PPI use: PPIs reduce iron absorption, so ask your prescriber whether you still need one; do not stop it on your own
  • Vegetarians/​vegans: heavier reliance on supplementation; pair non-heme iron with vitamin C; consider B12 too
  • Pregnancy: prenatal vitamins typically have iron; may need additional supplementation if deficient
  • Adolescent girls: especially vulnerable; check ferritin during heavy menses or athletic activity
โœ… Key Insight: Iron-deficiency anemia is often a sign of blood loss or poor absorption, not just inadequate intake.
Supplement Protocol

Evidence-Based Supplements for Iron-Deficiency Anemia

Iron form, dose and timing matter. Iron bisglycinate is often better tolerated. Alternate-day dosing may improve absorption.

SupplementWhat it is forTypical rangeTimingNotes & cautions
Iron Bisglycinate (Chelated)Better tolerated than ferrous sulfate. Less constipation, nausea. Possibly better absorbed.25 to 50 mg elemental iron daily OR every other dayEmpty stomach with vitamin CBest first-line for sensitive stomachs. The top of this range sits above the 45 mg/day tolerable upper intake level for adults. That is appropriate only when correcting a confirmed deficiency under clinical supervision, not as general supplementation. Test ferritin first, and retest rather than staying on it indefinitely.
Ferrous Sulfate (Traditional)Most studied form. Inexpensive. Effective but causes GI side effects. Alternate-day dosing absorbs better than daily. A dose of iron raises hepcidin, which reduces absorption of the next dose; in iron-depleted women, alternate-day dosing raised cumulative absorption from 16.3% to 21.8%.4325 mg (65 mg elemental iron) daily, or on alternate daysEmpty stomach if toleratedSide effects: nausea, constipation, dark stools. Start with food if needed. This sits above the 45 mg/day tolerable upper intake level for adults. That is appropriate only when correcting a confirmed deficiency under clinical supervision, not as general supplementation. Test ferritin first, and retest rather than staying on it indefinitely.
Heme Iron PolypeptideFrom animal source. Heme iron is absorbed more readily than non-heme iron.10 to 15 mg elemental iron 2 to 3x/dayWith or without foodMore expensive but well-tolerated.
Vitamin CStrongly enhances non-heme iron absorption8.250 to 500 mg with iron doseWith ironFood sources work too (orange juice, lemon water).
LactoferrinIron-binding protein. May increase iron absorption and improve symptoms even without raising hemoglobin much.100 to 300 mg/dayEmpty stomachNot a substitute for iron when iron is needed.
Vitamin B12Required for RBC maturation. Often a coexisting deficiency.1,000 mcg/day sublingualMorningTest level.
Folate (B9)Required for RBC production. Often combined with iron in prenatals.400 to 800 mcg folate/day (folic acid or methylfolate)With foodHigher doses in pregnancy. Check B12 before taking folate: folate can correct the blood count while B12 nerve damage carries on.
CopperRequired for iron mobilization from stores. Deficiency causes anemia.1 to 2 mg/day (rarely needed if eating varied diet)With food, away from zincWatch if taking high-dose zinc, which can deplete copper.
What to Expect

What to Expect Over Time

Iron treatment and the search for the cause usually run side by side.

Treatment and supportive care, together
First Weeks

Oral iron usually starts as soon as the deficiency is confirmed. Hemoglobin usually starts to rise within 2 weeks and is rechecked within the first 4 weeks. Constipation and dark stools are common; iron every other day or a different preparation is an option if daily tablets are not tolerated10.

Months 1 to 3

Hemoglobin returns to normal with iron treatment in most people. If it does not rise, a clinician considers intravenous iron and looks further for the cause.

Months 3 to 12

Treatment usually continues for about 3 months after hemoglobin is normal, to refill iron stores10. Whatever the investigations found, such as heavy periods, celiac disease or a bleeding source, is treated in its own right.

Long Term

Once stores are refilled, a blood count every 6 months or so at first helps catch a return of the deficiency, which happens in a minority. Anemia that comes back or does not respond calls for further tests, including of the small bowel.

When to Seek Care

Call 911 or go to the emergency department for vomiting blood, black tarry stools, chest pain, fainting or severe breathlessness. Iron tablets often turn stools dark green or black. Stools that are black, sticky and tar-like, or dark stools with dizziness, weakness or fainting, are an emergency. See a doctor promptly for blood in the stool. Men and postmenopausal women with new iron-deficiency anemia need their gut investigated even without other symptoms, because gut cancers can first show up this way3. Also go back if hemoglobin has not risen after 2 to 4 weeks of iron, or if symptoms return.

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Next Steps

Find the Cause, Then Replete

Iron-deficiency anemia is rarely "just diet." Always identify the cause: bleeding, malabsorption or intake. Treatment requires both addressing the cause and adequate iron repletion (often 3 to 6 months). Don't accept ongoing iron supplementation without finding and treating the underlying problem.

Explore Celiac Disease โ†’ Explore Gastritis โ†’

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed October 20, 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.9 This page is nutrition education, not medical advice, and it does not replace your doctor. The most important thing on this page is not a supplement. Iron-deficiency anemia in an adult man, a postmenopausal woman or a premenopausal woman with red flags requires endoscopy and colonoscopy to rule out a bleeding cancer. Colon and gastric cancers can present first as iron deficiency, and treating the anemia without finding the cause can delay that diagnosis. Iron supplements above the 45 mg/day tolerable upper intake level belong under clinical supervision, with ferritin tested first and retested rather than staying on them indefinitely.

  1. Global Burden of Disease Study anemia estimates and WHO global anemia data. PMC12338041 and PAHO/WHO. Anemia affects roughly 29.9% of women of reproductive age worldwide, 29.6% of nonpregnant women and 36.5% of pregnant women. Note that these figures count anemia from all causes; iron deficiency is the leading cause but not the only one, so anemia prevalence and IDA prevalence are not interchangeable. Anemia across the whole global population is lower, around 24%. ↩
  2. On iron deficiency in US women: an analysis of NHANES surveys of 8,200 nonpregnant women aged 20 to 45 found iron-deficiency anemia in 9.1% in 2021 to 2023, up from 4.3% in 1999 to 2000, and iron deficiency in 17.3% across the whole period, PubMed 41926767. Iron deficiency without anemia is considerably more common than IDA itself, which is why ferritin is worth checking before hemoglobin falls. ↩
  3. On the obligation to investigate: UK gastroenterology guidance reports that about a third of men and postmenopausal women with iron-deficiency anemia have an underlying disease, most often in the gut, that gut cancers can present this way, often without specific symptoms, and that examining both the upper and lower gut by endoscopy is the standard approach, PubMed 34497146. ↩
  4. Stoffel NU, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. Lancet Haematol. 2017;4(11):e524-⁠e533. PubMed 29032957, and Moretti D, et al. Blood. 2015;126(17):1981-⁠1989, ashpublications.org. A dose of oral iron raises serum hepcidin, which suppresses absorption of doses given over the following day. In iron-depleted women, cumulative fractional absorption was 21.8% on alternate-day dosing against 16.3% on consecutive days. The trial studied iron-depleted rather than anemic women, and its authors state plainly that the findings should be confirmed in iron-deficient anemic patients. ↩
  5. On ferritin thresholds: UK gastroenterology guidance explains that serum ferritin is the most specific test for iron deficiency when there is no inflammation, that a ferritin below 15 ยตg/L (15 ng/mL) indicates absent iron stores and below 30 ยตg/L generally indicates low stores, and that a cut-off of 45 ยตg/L has been suggested as the best balance in practice. Because ferritin rises with inflammation, a normal result can occur with iron deficiency in an inflammatory illness, and transferrin saturation can help when a falsely normal ferritin is suspected, PubMed 34497146. ↩
  6. On restless legs syndrome: current guidance recommends checking iron status in all RLS patients and offering iron when ferritin is at or below 75 µg/L, since RLS symptoms often respond to repletion even without anemia. The American Academy of Sleep Medicine's guideline advises testing ferritin and transferrin saturation in everyone with clinically significant RLS, and giving oral or intravenous iron when ferritin is 75 ng/mL or below or transferrin saturation is below 20%, a consensus threshold not yet tested in trials, PubMed 39324694. ↩
  7. On celiac screening: UK gastroenterology guidance reports celiac disease in 3 to 5% of people investigated for unexplained iron-deficiency anemia and recommends routine screening, serologically or by small bowel biopsy at gastroscopy, PubMed 34497146. ↩
  8. On absorption and inhibitors: Linus Pauling Institute Micronutrient Information Center, iron. lpi.oregonstate.edu. Heme iron makes up only 10 to 15% of dietary iron but may provide up to a third of the iron absorbed, and its absorption is less influenced by other foods, while non-heme iron absorption is strongly influenced by what it is eaten with. Polyphenols in coffee, black tea and herbal tea can markedly inhibit non-heme iron absorption, and vitamin C strongly enhances it. ↩
  9. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic. ↩
  10. On oral iron, monitoring and duration: UK gastroenterology guidance advises starting with one tablet a day of ferrous sulfate, fumarate or gluconate, moving to one tablet every other day or another preparation if that is not tolerated, checking for a hemoglobin response within the first 4 weeks, and continuing treatment for around 3 months after hemoglobin returns to normal to refill iron stores; where transfusion is needed for symptomatic anemia, iron treatment is still needed afterward, BSG guideline, 2021. ↩
  11. On the iron content of ferrous sulfate: a 325 mg ferrous sulfate tablet contains 65 mg of elemental iron, as stated on the product label, DailyMed product label. ↩
  12. On blood transfusion thresholds: international guidelines, based on 45 randomized trials in 20,599 adults, recommend considering transfusion in hospitalized adults who are hemodynamically stable when hemoglobin is below 7 g/dL, and allow a threshold of 8 g/dL for people with pre-existing cardiovascular disease, PubMed 37824153. ↩
  13. On finding the cause: UK gastroenterology guidance for adults reports that about a third of men and postmenopausal women with iron-deficiency anemia have an underlying disease, most often in the gastrointestinal tract, that celiac disease is found in 3 to 5% of cases, and that menstrual losses, pregnancy, poor intake, blood donation, long-term NSAID use and poor absorption are the other main contributors. It puts iron-deficiency anemia at 2 to 5% of adult men and postmenopausal women in the developed world, lists Helicobacter pylori infection among the causes of poor absorption, and notes that long-term proton pump inhibitor use may add to the risk, PubMed 34497146. ↩
  14. On liver in pregnancy: NHS guidance lists liver and liver products among the foods to avoid in pregnancy, because liver and foods containing it have high levels of vitamin A, which can be harmful to the baby, NHS, foods to avoid in pregnancy. ↩