Iron

• Treating iron-deficiency anemia (test ferritin and iron studies first)
• Correcting depleted iron stores before anemia develops
• Pregnancy and lactation, where requirements rise sharply
• Heavy menstrual bleeding
• Frequent blood donors
• Endurance athletes with confirmed low ferritin
• Plant-based eaters at documented risk, given lower non-heme absorption

Iron is an essential trace mineral with one of the broadest and most consequential biological roles of any nutrient. The total body iron content of approximately 3-4 grams is distributed primarily across three pools: functional iron (~70% of total, primarily as hemoglobin in red blood cells and myoglobin in skeletal and cardiac muscle), storage iron (~25%, primarily as ferritin in liver, spleen, and bone marrow), and transport iron (~0.1%, bound to transferrin in plasma). The functional role centers on oxygen transport, hemoglobin's four iron-containing heme groups bind oxygen in pulmonary capillaries and release it at peripheral tissues, with myoglobin providing oxygen storage in muscle tissue. Beyond oxygen transport, iron serves as cofactor for cytochrome P450 enzymes (drug metabolism), the mitochondrial electron transport chain (ATP production), ribonucleotide reductase (DNA synthesis), and numerous other iron-dependent enzymes. The breadth of iron-dependent biology means iron deficiency produces multisystem manifestations, fatigue, cognitive impairment, immune dysfunction, hair loss, restless leg syndrome, exercise intolerance, that often precede the classical anemia diagnostic threshold. Iron homeostasis is uniquely regulated among minerals because the body lacks efficient iron excretion. Daily iron loss is small (~1-2mg/day in non-menstruating adults; substantially more in menstruating women, pregnancy, blood donation, GI bleeding) and dietary absorption is tightly controlled through hepcidin, a hepatic peptide hormone that regulates iron entry into circulation. Hepcidin reduces iron absorption in iron-replete states and during inflammation; this elegant regulation produces the contradiction central to iron supplementation: routine excess is prevented at the gut level, but iron overload (genetic hemochromatosis, multiple transfusions) can produce severe organ damage when this regulatory system is bypassed or overwhelmed. The two dietary iron forms, heme iron (from animal sources, 25-30% absorbed) and non-heme iron (from plant sources and supplements, 5-10% absorbed), have substantially different bioavailability and interact with different absorption inhibitors (calcium, phytates, tannins reduce non-heme absorption; heme iron is relatively unaffected). This bioavailability difference has substantial implications for vegetarian and vegan iron supplementation strategies. The clinical iron deficiency epidemic is the most common nutrient deficiency globally, affecting an estimated 2 billion people including reproductive-age women in both developed and developing countries, and remains among the most consequential nutritional public health challenges.

Iron dosing has undergone substantial evolution following the Stoffel 2017 Lancet Haematology trial demonstrating that alternate-day dosing produces superior cumulative absorption versus daily dosing in iron-deficient women. The mechanism: each iron dose triggers hepcidin elevation that suppresses iron absorption for ~24-48 hours; daily dosing essentially fights against hepcidin response, while alternate-day dosing allows hepcidin to fall between doses. Modern recommendations increasingly favor 80-150mg elemental iron every other day (or 3 times weekly) over the traditional 65mg three times daily. Take with vitamin C (orange juice, ascorbic acid 250mg) to enhance non-heme iron absorption substantially. Avoid concurrent calcium, dairy, coffee, tea, and high-phytate foods (all reduce non-heme iron absorption). Iron should be taken on an empty stomach when tolerated; food reduces absorption ~50% but may improve GI tolerability. For mild iron deficiency (sub-anemic), 18-36mg elemental iron daily-alternate days is often adequate; clinical iron deficiency anemia typically requires 65-200mg elemental iron daily or alternate-day for 3-6 months with hemoglobin and ferritin monitoring. Iron repletion proceeds through hemoglobin normalization (4-8 weeks) followed by storage iron repletion (additional 3-6 months). Premature discontinuation before storage repletion is a common cause of recurrent iron deficiency anemia. The Upper Limit (45mg/day adults; 40mg/day children) reflects GI tolerance more than systemic toxicity in users with normal iron status; users with hereditary hemochromatosis should not exceed dietary iron levels.

RDA adult men

8mg/day

RDA adult women (reproductive age)

18mg/day

RDA pregnancy

27mg/day

Upper Limit (UL) adults

45mg/day

IDA treatment dose

65-200mg elemental iron daily-alternate days

Modern protocol (post-Stoffel 2017)

80-150mg elemental iron every other day

Sub-anemic deficiency

18-36mg/day or alternate days

Treatment duration

3-6 months past hemoglobin normalization

• Ferrous Sulfate

  Rating: good

  The standard pharmaceutical iron form, used in essentially every major iron deficiency anemia trial. Delivers 65mg elemental iron per 325mg tablet (20% elemental iron content). Substantially superior absorption versus ferric forms; substantial GI side effects in many users (nausea, constipation, dark stools, metallic taste). Cheap, effective, and well-evidenced, but tolerability is the main limitation.

• Ferrous Fumarate

  Rating: good

  Alternative ferrous salt with similar elemental iron content (33%) and absorption versus sulfate. Slightly different GI side effect profile; some users tolerate fumarate better than sulfate. Acceptable alternative for clinical iron repletion.

• Ferrous Gluconate

  Rating: good

  Lower elemental iron content (12%) than sulfate or fumarate; often better-tolerated GI profile. Reasonable for users requiring iron supplementation but unable to tolerate higher-elemental forms. Slower hemoglobin response due to lower elemental dose.

• Iron Bisglycinate (Chelate)

  Rating: gold

  Amino acid chelate form (Albion/Balchem Ferrochel brand or generic equivalents) with substantially reduced GI side effects versus ferrous salts. Absorption equivalent or superior to ferrous sulfate at typical doses. Increasingly preferred for daily supplementation in users requiring iron but seeking better tolerability. Premium pricing but generally justified by tolerability advantage.

• Heme Iron Polypeptide (Proferrin)

  Rating: gold

  Bovine-source heme iron preparation with absorption profile similar to dietary heme iron (~30%, not affected by typical absorption inhibitors). Substantially better-tolerated than ferrous salts. Higher cost; not suitable for vegan/vegetarian users.

• Polysaccharide-Iron Complex (Niferex, Nu-Iron)

  Rating: good

  Iron complexed to a polysaccharide carrier. Generally well-tolerated; absorption acceptable. Available in higher elemental iron doses per pill (150mg) supporting once-daily dosing. Common prescription iron formulation.

• IV Iron (Venofer, Injectafer, Monoferric)

  Rating: gold

  Intravenous iron formulations for users unable to tolerate or absorb oral iron, with significant ongoing blood loss, or with severe iron deficiency requiring rapid repletion. Modern IV iron formulations (Injectafer, Monoferric) allow single high-dose administration. Specialist coordination required; rare anaphylaxis history (older dextran formulations).

• Carbonyl Iron (Feosol Caplet)

  Rating: good

  Elemental iron powder form. Acid-dependent absorption produces somewhat slower release with reduced acute GI toxicity. Substantial overdose safety advantage (much higher LD50 than ferrous salts), relevant for households with children.

• Iron deficiency anemia (men and post-menopausal women)

  Strength of evidence for this group: strong

  Workup is critical, iron deficiency in this cohort warrants GI bleeding evaluation. Supplementation is straightforward (ferrous sulfate or alternative), 3-6 months treatment, follow-up with hemoglobin and ferritin. Etiology investigation often more important than the supplementation itself.

• Reproductive-age women (menstruating)

  Strength of evidence for this group: strong

  The most common iron-deficient cohort globally. Menstrual blood loss exceeds dietary iron replacement in many women; iron deficiency without anemia is widespread. Stoffel 2017 alternate-day dosing produces superior cumulative absorption in this cohort. Reasonable to assess ferritin and supplement at sub-anemic deficiency thresholds (ferritin <30 ng/mL).

• Pregnancy

  Strength of evidence for this group: strong

  WHO recommends routine iron supplementation in pregnancy globally (30-60mg daily based on local anemia prevalence). Pregnancy iron requirements increase substantially (RDA 27mg vs 18mg non-pregnant). The challenge is GI tolerability, pregnancy nausea + iron GI effects compound. Alternate-day dosing, bisglycinate forms, or food-based strategies often more tolerable than standard prescription daily iron.

• Athletes (endurance, female athletes especially)

  Strength of evidence for this group: modest

  Sub-anemic iron deficiency reduces endurance performance and cognitive function. Pasricha 2014 and subsequent work support exercise performance improvements with iron supplementation in iron-deficient (non-anemic) women. Assess ferritin in symptomatic athletes; supplement at ferritin <30 ng/mL. Excessive supplementation in iron-replete athletes is not warranted.

• Children (especially 6-24 months)

  Strength of evidence for this group: strong

  McCann 2007 and substantial subsequent evidence establishes cognitive and developmental consequences of iron deficiency in children. WHO and pediatric guidance support routine iron supplementation in at-risk populations and iron-fortified foods. Pediatric coordination for dosing; iron overdose in children is a real clinical concern (carbonyl iron has safety advantage).

• Restless legs syndrome (low ferritin)

  Strength of evidence for this group: modest

  Iron deficiency (ferritin <75 ng/mL) is associated with restless legs syndrome; supplementation in this cohort can reduce symptoms substantially. Neurology coordination for established RLS; ferritin assessment in symptomatic users without other identified iron deficiency.

• Hereditary hemochromatosis

  Strength of evidence for this group: cautious

  Genetic iron overload disorder (HFE C282Y homozygotes most common). CONTRAINDICATED for iron supplementation; standard treatment is therapeutic phlebotomy. Family screening warranted. Specialist coordination through hematology.

• Healthy adults with normal iron status

  Strength of evidence for this group: cautious

  Routine iron supplementation in iron-replete adults without specific indication is not warranted and may be harmful (oxidative stress, theoretical chronic disease associations at elevated ferritin levels). Multivitamins with iron are reasonable for at-risk groups; targeted iron supplementation requires ferritin assessment.

• Inflammatory conditions / anemia of chronic disease

  Strength of evidence for this group: cautious

  Hepcidin elevation in chronic inflammation impairs iron absorption and utilization. Oral iron is often ineffective in this context; IV iron or treatment of underlying inflammation may be needed. Coordinate with treating clinician (gastroenterology, rheumatology, nephrology depending on context).

• Vitamin C (Ascorbic Acid)

  Interaction: synergy

  The signature iron pairing. Vitamin C reduces ferric (Fe3+) to ferrous (Fe2+) iron at the intestinal brush border, substantially enhancing non-heme iron absorption. 250mg ascorbic acid with iron dose, or take iron with orange juice. Effect more pronounced for plant-source iron and supplemental iron than for heme iron.

• Calcium

  Interaction: caution

  Calcium substantially reduces non-heme iron absorption when taken concurrently. Separate iron and calcium supplements by 2-4 hours; avoid taking iron with dairy or calcium-fortified beverages. Clinically relevant interaction in users requiring both supplements.

• Zinc

  Interaction: caution

  Iron and zinc compete for absorption at the intestinal level. Take iron and zinc at separate meals when both are supplemented. Clinical interaction is modest at typical doses but supplementation timing matters.

• Coffee / Tea (Tannins)

  Interaction: caution

  Tannins in coffee and tea reduce non-heme iron absorption by 50-90% when consumed concurrently. Substantial clinical relevance for tea-drinking populations with marginal iron status. Take iron supplements 1-2 hours away from coffee or tea.

• Phytates (Whole Grains, Legumes)

  Interaction: caution

  Phytic acid in whole grains, legumes, nuts, and seeds reduces non-heme iron absorption. Fermentation, sprouting, and soaking reduce phytate content. Relevant for vegetarian and vegan iron strategies.

• Proton Pump Inhibitors / H2 Blockers

  Interaction: caution

  Reduced gastric acid impairs iron absorption (particularly non-heme forms). Chronic PPI/H2 use is associated with iron deficiency; supplementation may be needed with absorption enhancers (vitamin C) or alternative routes (IV iron, heme iron polypeptide).

• Levothyroxine

  Interaction: caution

  Iron substantially reduces levothyroxine absorption. Separate doses by 4 hours; clinically important interaction in users on thyroid replacement therapy.

• Quinolone and Tetracycline Antibiotics

  Interaction: caution

  Iron chelates with these antibiotics reducing absorption substantially. Separate dosing by 2-6 hours.

• Hereditary Hemochromatosis

  Interaction: avoid

  CONTRAINDICATED. Iron supplementation in HFE C282Y homozygotes and other iron overload conditions can accelerate organ damage. Specialist coordination through hematology essential.

Look for: explicit elemental iron content (not just compound weight) on label; specific iron compound disclosed (ferrous sulfate, fumarate, gluconate, bisglycinate); USP verification for clinical-grade products; child-resistant packaging (essential for households with children); vitamin C inclusion or recommendation for absorption enhancement; reasonable price per mg elemental iron. Avoid: products without elemental iron disclosure; products combining iron with calcium or zinc in single dose (absorption interference); products marketed primarily for general "energy" without iron deficiency indication; high-dose iron in households with children without secure storage. For users prioritizing GI tolerability, bisglycinate forms generally justify modest premium pricing; for cost-conscious users with normal GI tolerance, ferrous sulfate remains the most cost-effective evidence-based option.

Iron's biological essentiality was established through stepwise discovery across 250 years of medical and chemical research. Vincenzo Menghini's 1747 demonstration of iron in dried blood ash at the University of Bologna provided the first analytical confirmation that blood contained iron. Felix Hoppe-Seyler's 1862 crystallization of hemoglobin and characterization of its iron-containing structure established the molecular basis. The clinical era of iron supplementation for "chlorosis" (the classical description of iron deficiency anemia in young women) developed through the 19th century, with iron preparations widely used in Victorian medical practice. The modern epidemiologic understanding of global iron deficiency developed through 20th century population studies. The WHO global assessment work consolidating ~2 billion people affected globally established iron deficiency as the most common nutrient deficiency in human nutrition. Public health interventions developed substantial scope, iron-fortified flour and cereal in many countries, iron-folic acid supplementation in pregnancy programs globally, iron supplementation in pediatric infectious disease programs (particularly in malaria-endemic regions where iron supplementation has complex risk-benefit considerations). The cognitive and developmental iron evidence base developed substantially through the 2000s. McCann 2007 and subsequent meta-analyses established cognitive and behavioral consequences of iron deficiency particularly in children. The behavioral consequences (irritability, attention deficits, reduced learning capacity) were as important as the physical consequences (fatigue, exercise intolerance) for public health prioritization. The Pasricha 2014 Lancet trial established sub-anemic iron deficiency as a clinically meaningful entity warranting supplementation, challenging the traditional view that only anemic iron deficiency required treatment. This evidence supported the modern practice of ferritin-guided supplementation at thresholds below hemoglobin-defined anemia. The Stoffel 2017 alternate-day dosing finding was a substantial shift in clinical practice. The traditional daily-dose paradigm was based on absorption studies that did not account for hepcidin dynamics; Stoffel demonstrated that alternate-day dosing produces superior cumulative absorption by allowing hepcidin to fall between doses. Implementation has been gradual; many clinicians still use daily dosing while research continues to support alternate-day approaches. IV iron has undergone substantial evolution. Older iron dextran formulations had concerning anaphylaxis rates; modern formulations (Venofer iron sucrose, Injectafer ferric carboxymaltose, Monoferric ferric derisomaltose) have substantially improved safety profiles and allow single-dose high-dose administration for users unable to tolerate or absorb oral iron. The story of iron in human nutrition remains substantially unresolved, the global burden of iron deficiency persists despite mature understanding of pathophysiology, accessible interventions, and clear public health rationale for intervention. Implementation challenges (tolerability, cost in low-income settings, complex risk-benefit in infectious disease contexts) continue to limit progress.

1. 1747Menghini demonstrates iron in dried blood ash (Bologna)
2. 1862Hoppe-Seyler crystallizes hemoglobin; iron-oxygen role established
3. 1932Heath establishes oral iron supplementation in iron deficiency anemia
4. 1950s-70sIron deficiency global epidemiology characterized; food fortification programs
5. 1998US folic acid fortification (with continued iron fortification)
6. 2001AREDS macular degeneration formulation (not primarily iron but related antioxidant context)
7. 2007McCann iron-cognition meta-analysis
8. 2009McLean WHO global iron deficiency assessment
9. 2014Pasricha sub-anemic iron deficiency exercise trial
10. 2015Stoltzfus pregnancy Cochrane review; Camaschella NEJM clinical review
11. 2017Stoffel alternate-day dosing paradigm shift
12. 2020sModern IV iron formulations widespread (Injectafer, Monoferric)

• Whether alternate-day dosing (Stoffel 2017) will fully replace traditional daily dosing in clinical practice, implementation has been gradual, and patient adherence to alternate-day schedules has its own challenges.
• Whether iron supplementation should be guided by serum ferritin alone or by additional markers (transferrin saturation, hepcidin, soluble transferrin receptor) in complex cases.
• Whether sub-anemic iron deficiency thresholds (ferritin <30 ng/mL vs <50 ng/mL vs <75 ng/mL) should be standardized across guidelines, current variability creates clinical practice variation.
• Whether routine population-level iron screening should be expanded, current US screening is limited; broader screening might identify many sub-anemic deficiency cases warranting intervention.
• How best to manage iron in inflammatory bowel disease, oral iron may exacerbate intestinal inflammation; IV iron is often preferred but adds cost and complexity.
• Whether emerging iron formulations (Sucrosomial Iron, Maltol Iron, etc.) produce clinically meaningful advantages versus established bisglycinate and ferrous salt options.
• The cognitive and behavioral implications of iron deficiency in older adults, much research has focused on children, less on geriatric cognitive iron biology.
• Whether male iron supplementation guidance should be more conservative given lower physiological requirements and theoretical chronic disease associations with elevated iron stores.

Universally available globally as dietary supplement, over-the-counter pharmaceutical, prescription pharmaceutical, and food fortification. Legal under DSHEA in the United States and equivalent regulations globally. Not on WADA prohibited list. Pharmaceutical iron formulations (ferrous sulfate, ferrous fumarate, polysaccharide-iron) are available OTC and by prescription depending on dose. IV iron formulations (Venofer, Injectafer, Monoferric) require specialist administration. Major retail brands include Slow Fe (controlled release ferrous sulfate), Feosol (ferrous sulfate, carbonyl iron variant), Nature Made, Vitron-C, Niferex (polysaccharide-iron), and chelated bisglycinate from multiple manufacturers (Solgar, Pure Encapsulations, Thorne, Designs for Health). Food fortification programs (cereal, flour) in the United States and many other countries provide substantial public health iron at population level. The iron supplementation category is mature commercially with established product differentiation around tolerability and absorption.

Status current as of July 2026. Regulatory positions change, sometimes quickly.

Status

Essential trace mineral

Total body content

3-4 grams

Functional iron

~70% (hemoglobin, myoglobin)

Storage iron

~25% (ferritin)

Heme iron absorption

25-30% (animal sources)

Non-heme iron absorption

5-10% (plant sources, supplements)

What follows is unfinished work on our side, not a finding about Iron. A short entry is not a safe entry.

• Cost and market. We have not documented what it sells for or who sells it.
• Supply chain. We have not mapped where it is made.
• Who uses it. We have not documented the user groups.
• What could change. No forward-looking summary yet.
• How it compares. We have not set it against the alternatives.
• Children and teenagers. We have not checked what is known about younger people.
• Where we land. We have not taken a position on this yet.