Mineral ·Strong evidence ·Reviewed May 2026
Essential for oxygen transport via hemoglobin, energy production, and immune function. Most common nutritional deficiency worldwide, especially in women.
The bottom line
Evidence rating strong. Most-documented uses: oxygen transport, energy production, immune function. 21 sources indexed (2003–2025), with 57 interaction records on file.
Core mechanism
Central atom in heme groups of hemoglobin (carries oxygen in red blood cells) and myoglobin (stores oxygen in muscle). Component of cytochrome enzymes in the electron transport chain for ATP production. Required for DNA synthesis and immune cell proliferation.1,6
Take on empty stomach with 50-100mg vitamin C for best absorption; avoid with calcium, tea, or coffee. Alternate-day morning dosing may provide 33% higher cumulative absorption due to hepcidin cycling.1,3
Dosing protocol
Use for a defined repletion period and then reassess ferritin rather than taking indefinitely. Doses above 45 mg/day should be clinician-supervised.1
Ranked by evidence and value.
Real-world pricing across three quality tiers. Assumes Ferrous Sulfate.
Assumes about 18-45 mg elemental iron/day unless a clinician directs higher dosing. Ferrous sulfate is usually cheapest, but GI side effects can make it a false economy if adherence drops. Updated 2026-04-02.
How much you'd eat to match a supplemental dose.
Heme iron from animal foods is absorbed much better than non-heme iron from plants.
Food-first approaches work best when deficiency is mild or prevention is the goal.
Dose: 18-45 mg elemental iron daily1,7
Timing: Empty stomach if tolerated; otherwise with a light meal
Take away from calcium, magnesium, zinc, coffee, tea, and fiber. Doses above 45 mg/day should be clinician-supervised with labs.
What to test, the optimal window inside the conventional range, and how long a response takes.
Effective iron repletion should raise ferritin gradually without overshooting into overload.6,8
Interpret with CBC and transferrin saturation; inflammation can raise ferritin independent of iron status.
Serum iron should rise as deficiency improves, but it is a volatile marker.1,7
A fasting morning sample is preferred for trend comparisons.
TIBC often trends down as iron deficiency is corrected.1,2
Best interpreted with serum iron and transferrin saturation.
Transferrin saturation should rise as available iron improves.
Fasting sampling improves consistency for follow-up.
Iron supplementation raises hemoglobin specifically when low iron stores are limiting red blood cell production, as in iron-deficiency anemia, because iron is the core component of the hemoglobin molecule that carries oxygen. In people who are not iron deficient, adding iron does not push hemoglobin higher and can cause harm, so the benefit applies only to correcting a documented deficiency.1,6
Hemoglobin does not require fasting and can be drawn at any time of day. Do not judge iron's effect by hemoglobin alone: pair it with ferritin and a transferrin saturation or iron panel to confirm that low iron is the actual cause before and during treatment. Oral iron is best absorbed on an empty stomach and is helped by vitamin C, while calcium, coffee, tea, and antacids reduce absorption, so separate them by a couple of hours. Anemia is a medical condition: have a clinician confirm the diagnosis, identify why iron is low (which can signal blood loss or other issues), set the dose, and decide how long to continue, rather than self-treating.
Where this appears in the symptom-to-supplement map, ranked by relevance.
Untreated celiac damages the duodenum where iron is absorbed, so iron deficiency anemia is the most common deficiency at diagnosis and replacing iron corrects it.8,9
Adjunct to gluten-free diet, not a substitute; dose against ferritin and CBC ordered by your clinician, and recheck after mucosal healing since needs often fall.
Iron supports oxygen transport and mitochondrial energy production, making it one of the first nutrients to check in fatigue.16,17
Check ferritin before supplementing.
Low ferritin is a classic contributor to restless legs syndrome.6,16
Check ferritin before supplementing; many clinicians target a ferritin well above the deficiency cutoff.
Low ferritin is a common reversible contributor to diffuse hair shedding.6,16
Check ferritin before supplementing.
Iron is required for hemoglobin and oxidative enzymes, so deficiency directly impairs oxygen delivery and aerobic endurance, especially in menstruating and endurance athletes.12,1
Only supplement after confirming low ferritin via blood test; iron overload is harmful, so do not take blindly.
Low iron and ferritin are a common reversible driver of hair shedding and poor hair quality, especially in menstruating women.6,16
Check ferritin before supplementing, since iron mainly helps when stores are low.
Low iron or ferritin reduces oxygen delivery and can impair focus and mental stamina.6,16
Ferritin is usually the most useful first lab.
Iron deficiency and anemia reduce oxygen-carrying capacity and can drive lightheadedness on standing, so repletion addresses a common underlying cause.1,7
Only supplement after a ferritin and CBC confirm deficiency, since unnecessary iron can cause overload and GI side effects.
Low iron or ferritin can produce a pale, sallow periorbital area that makes underlying vessels look darker.6,16
Check ferritin first and only supplement if it is low, since excess iron is harmful; see a clinician for unexplained fatigue or anemia.
Iron is required for the hypoxia-driven rise in red blood cell production at altitude, so adequate stores may support acclimatization, especially in those who are iron deficient.1,2
Test iron status first and supplement only if stores are low, since excess iron is harmful; a clinician can guide this.
Iron deficiency can cause angular cheilitis and mucosal changes by impairing epithelial cell turnover, so correcting deficiency often improves symptoms.1,2
Only supplement iron if testing confirms deficiency; excess iron is harmful, so get bloodwork through a clinician first.
Iron deficiency can cause brittle, ridged, or spoon-shaped (koilonychia) nails and slow growth.1,2
Check ferritin first; spoon-shaped nails are a flag to see a clinician.
Evidence-based stacks that include it, with the exact dose and timing each one uses.
Low iron stores (ferritin) are associated with telogen hair shedding, especially in menstruating women, and repletion can help in that specific case; iron should be guided by ferritin testing and not taken blindly, since excess iron is harmful.6,16
Iron is required for thyroid peroxidase, the enzyme that catalyzes thyroid hormone synthesis, so low iron can blunt hormone output and contribute to fatigue. Supplement only when bloodwork shows low or borderline iron, since unneeded iron carries an overload risk.1,2
Iron is essential for hemoglobin and myoglobin and for mitochondrial oxidative enzymes, so deficiency directly limits oxygen transport and aerobic capacity. Supplementation reliably improves endurance only when iron deficiency is confirmed by testing, and unnecessary use carries a risk of iron overload, so it should not be taken empirically.1,6
Adequate iron status supports building reserves ahead of pregnancy, and low intake of nonheme iron has been linked to ovulatory concerns in observational work. Iron should not be supplemented routinely without confirming need, since excess can cause harm, so testing and clinician guidance are advised.4,7
HFE variants increase the risk of iron loading, so routine iron supplementation can overshoot ferritin or transferrin saturation in susceptible people.
Recommendation: Avoid empiric iron unless CBC, ferritin, and transferrin saturation support deficiency; monitor iron studies if an HFE variant is known.
Vitamin C dramatically increases non-heme iron absorption by reducing ferric iron (Fe3+) to ferrous iron (Fe2+) and forming a soluble chelate.
Recommendation: Take 50-100mg+ vitamin C with iron supplements to maximize absorption (higher doses showed no further benefit). Especially important for plant-based iron sources.
Calcium significantly inhibits both heme and non-heme iron absorption when taken simultaneously.
Recommendation: Separate iron and calcium by at least 2 hours. Take iron in the morning on an empty stomach, calcium with a different meal.
Iron and zinc compete for the same absorption pathways when taken together in supplement form.
Recommendation: Take iron and zinc at different times of day, separated by at least 2 hours.
Both iron and B12 are essential for red blood cell production. Deficiency in either causes anemia.
Recommendation: If anemic, check both iron and B12 status. Supplementing only one may not resolve anemia if both are deficient.
Iron is a cofactor for tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis.
Recommendation: Ensure adequate iron status when using L-tyrosine for cognitive support. Iron deficiency impairs catecholamine synthesis.
ALA chelates metals including iron. May reduce iron absorption or redistribute iron stores.
Recommendation: Separate by 2+ hours. Avoid high-dose ALA if you have iron deficiency.
Iron supplements can disrupt gut microbiome composition. However, certain probiotic strains may actually enhance iron absorption.
Recommendation: Separate by 2 hours. Some Lactobacillus strains can increase iron absorption, so probiotics may be beneficial for iron-supplementing individuals.
Vitamin A improves iron mobilization from stores and enhances erythropoiesis. Combined supplementation is more effective than either alone for anemia.
Recommendation: Supplementing both is more effective for iron-deficiency anemia than iron alone, especially in developing countries.
Magnesium and iron can compete for absorption when taken together. Separate for optimal absorption of both.
Recommendation: Take iron in the morning on an empty stomach. Take magnesium glycinate in the evening.
Iron deficiency impairs thyroid hormone synthesis because thyroid peroxidase (TPO) is a heme-containing enzyme.
Recommendation: Address iron deficiency when treating thyroid issues. Iron-deficient individuals may not respond well to iodine supplementation alone.
Ashwagandha root contains natural iron and has been shown to support healthy iron levels and hemoglobin formation in traditional use.
Recommendation: Ashwagandha may complement iron supplementation for mild iron deficiency, but is not a substitute for iron therapy in significant deficiency.
Vitamin C Liposomal dramatically increases non-heme iron absorption by reducing ferric iron (Fe3+) to ferrous iron (Fe2+) and forming a soluble chelate.
Recommendation: Take 50-100mg+ vitamin C with iron supplements to maximize absorption (higher doses showed no further benefit). Especially important for plant-based iron sources.
Numbered references. Citations throughout the page link here.
In 28 studies with 8,829 participants, pooled Hb improvement was 2.01 g/dL (95% CI 1.48-2.54). Low-dose iron (<5 mg/kg/day) with treatment durations <3 months or >6 months was optimal for improving hemoglobin levels.
Chan B, Varghese A, Badve SV et al.. Systematic Review of the Effects of Iron on Cardiovascular, Kidney, and Safety Outcomes in Patients With CKD. Kidney international reports. 2025
Fiani D, Chahine S, Zaboube M et al.. Psychiatric and cognitive outcomes of iron supplementation in non-anemic children, adolescents, and menstruating adults: A meta-analysis and systematic review. Neuroscience and biobehavioral reviews. 2025
Fauzan R, Defrin, Susmiati et al.. Impact of TMPRSS6 Genetic Variants on Maternal Iron Status in Pregnancy: A Systematic Review. Birth defects research. 2025
Iron supplementation significantly improved intelligence, attention and concentration, and memory in school-age children across 13 studies
In 17 RCTs, ferrous bisglycinate resulted in higher hemoglobin in pregnant women (SMD 0.54 g/dL, P<0.01) and fewer GI adverse events (IRR 0.36, P<0.01) compared to other iron supplements.
In 8 RCTs with 2,822 women, daily oral iron supplementation in pregnancy reduced iron deficiency anemia at term (RR 0.51, 95% CI 0.38-0.70) and low birthweight incidence (RR 0.30, 95% CI 0.13-0.68).
Skolmowska D, Głąbska D, Kołota A et al.. Effectiveness of Dietary Interventions to Treat Iron-Deficiency Anemia in Women: A Systematic Review of Randomized Controlled Trials. Nutrients. 2022
Skolmowska D, Głąbska D, Kołota A et al.. Effectiveness of Dietary Interventions in Prevention and Treatment of Iron-Deficiency Anemia in Pregnant Women: A Systematic Review of Randomized Controlled Trials. Nutrients. 2022
Daily iron supplementation effectively improved iron status and reduced anaemia in menstruating women
Ferrous sulfate significantly increased GI side-effect risk vs placebo (OR 2.32) and vs IV iron (OR 3.05)
Iron supplementation improved VO2max and submaximal exercise performance in women of reproductive age
Fatigue decreased by 47.7% in iron group vs 28.8% in placebo (p=0.02) in 198 non-anaemic women with ferritin <50 ug/L
Fatigue decreased 29% in iron group vs 13% in placebo (p=0.004); benefit restricted to women with ferritin <=50 ug/L
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