Best Iron Supplements 2025
Evidence-based reviews of the top iron supplements for energy and blood health
CRITICAL SAFETY INFORMATION
- • Iron overdose is dangerous and can be fatal, especially in children. Keep iron supplements out of reach of children.
- • Get blood work before supplementing. Iron is only beneficial if you are deficient.
- • Men and postmenopausal women should NOT take iron supplements without medical indication.
- • Excess iron can damage organs including the heart, liver, and pancreas.
- • Consult a healthcare provider before starting iron supplementation.
Understanding Iron Supplementation
Iron is an essential mineral necessary for producing hemoglobin, the protein in red blood cells that carries oxygen throughout the body. Iron deficiency is the most common nutrient deficiency worldwide, affecting approximately 1.6 billion people. Iron deficiency anemia causes fatigue, weakness, pale skin, shortness of breath, and impaired cognitive function.
However, iron supplementation is not appropriate for everyone. The body has limited ability to excrete excess iron, so too much iron accumulates in organs and can cause serious health problems. According to the World Health Organization, iron supplementation should be based on demonstrated need through blood testing, not taken preemptively. Serum ferritin and complete blood count tests can determine if supplementation is warranted.
Different forms of iron have varying absorption rates and tolerability. Ferrous sulfate is the most studied but often causes gastrointestinal side effects. Newer chelated forms like ferrous bisglycinate offer better absorption with fewer side effects. Heme iron, derived from animal sources, is absorbed more efficiently than non-heme iron from plant sources.
Who Should NOT Take Iron Supplements: Men and postmenopausal women typically do not need iron supplements unless diagnosed with deficiency. People with hemochromatosis (genetic iron overload disorder), thalassemia, or chronic kidney disease should not take iron without medical supervision. Always get blood work before supplementing with iron.
Quick Comparison
| Rank | Product | Form | Amount | Price | Rating |
|---|---|---|---|---|---|
| #1 | Thorne Research Iron Bisglycinate Thorne | Ferrous Bisglycinate | 25mg elemental iron | $11-15 (60 capsules) | ★4.8 |
| #2 | Slow Fe Iron Tablets Slow Fe | Ferrous Sulfate (slow-release) | 45mg elemental iron | $10-14 (60 tablets) | ★4.6 |
| #3 | Feosol Complete with Bifera Feosol | Heme + Non-heme (Bifera) | 28mg elemental iron | $15-20 (30 capsules) | ★4.5 |
| #4 | MegaFood Blood Builder MegaFood | Whole Food Iron | 26mg elemental iron | $24-32 (90 tablets) | ★4.6 |
| #5 | Nature Made Iron 65mg Nature Made | Ferrous Sulfate | 65mg elemental iron | $6-9 (180 tablets) | ★4.4 |
Thorne Research Iron Bisglycinate
Thorne Research uses ferrous bisglycinate, a chelated form of iron that research shows has superior bioavailability and tolerability compared to ferrous sulfate. The chelation protects iron from interacting with other dietary components that can inhibit absorption. Studies suggest bisglycinate is absorbed intact through a different mechanism than non-chelated iron, reducing the gastrointestinal side effects like nausea and constipation that are common with other iron supplements.
Supplement Facts
Key Features
- Highly absorbable bisglycinate chelate
- Gentle on the stomach
- NSF Certified for Sport
- No constipation reported by most users
Pros & Cons
Pros:
- +Excellent bioavailability without GI distress
- +Well-tolerated compared to ferrous sulfate
Cons:
- -More expensive than basic iron
- -May need higher doses for severe deficiency
Slow Fe Iron Tablets
Slow Fe uses ferrous sulfate in a controlled slow-release formula designed to deliver iron gradually throughout the day. This reduces the sudden spike in iron levels that can cause stomach upset with regular ferrous sulfate. While ferrous sulfate is not as well-tolerated as bisglycinate, the slow-release mechanism helps minimize common side effects. The 45mg elemental iron per tablet is appropriate for correcting iron deficiency under medical supervision.
Supplement Facts
Key Features
- Controlled slow-release formula
- Reduces stomach upset compared to regular ferrous sulfate
- Time-tested brand
- Special coating for gradual absorption
Pros & Cons
Pros:
- +Slow-release reduces GI side effects
- +Higher iron content for deficiency correction
Cons:
- -Still may cause constipation in some users
- -Should be taken on empty stomach for best absorption
Feosol Complete with Bifera
Feosol Complete uses Bifera technology, combining heme iron (derived from animal hemoglobin) and polypeptide iron. Research shows that heme iron, the form found in meat, is absorbed 2-3 times more efficiently than non-heme iron from plants. By combining both forms plus vitamin C, this product aims to maximize absorption while maintaining tolerability. Studies indicate that heme iron is less affected by dietary inhibitors like phytates and tannins.
Supplement Facts
Key Features
- Combines heme iron and polypeptide iron
- Includes vitamin C (60mg) for enhanced absorption
- Based on research on heme vs non-heme iron
- Designed for maximum absorption
Pros & Cons
Pros:
- +Dual iron sources may optimize absorption
- +Vitamin C enhances iron uptake
Cons:
- -Higher price per serving
- -Heme iron is derived from animal sources (not vegetarian)
MegaFood Blood Builder
MegaFood Blood Builder provides iron from whole food sources including organic spinach and beets, combined with folate and vitamin B12 for comprehensive blood health support. The whole food approach may be gentler on the digestive system, and the formula is designed to be taken any time of day, even on an empty stomach. While whole food iron is absorbed differently than isolated iron salts, studies on whole food supplements show they can effectively support iron status when used consistently.
Supplement Facts
Key Features
- Whole food iron from organic foods
- Includes folate (400mcg) and B12 (8mcg)
- Beetroot for additional blood support
- Certified vegan and gluten-free
Pros & Cons
Pros:
- +Gentle whole food formula
- +Comprehensive blood health support with B vitamins
Cons:
- -Higher price point
- -Slower to raise iron levels than higher-dose options
Nature Made Iron 65mg
Nature Made Iron provides 65mg of elemental iron from ferrous sulfate, the most commonly studied form of iron supplementation. While ferrous sulfate is well-absorbed, it commonly causes gastrointestinal side effects including nausea, constipation, and stomach upset. The USP verification ensures that the product contains what it claims and meets quality standards. This is an appropriate choice for those who tolerate ferrous sulfate well and need an affordable option for correcting iron deficiency under medical supervision.
Supplement Facts
Key Features
- High potency ferrous sulfate
- USP verified for quality
- Most affordable option
- Widely available in stores
Pros & Cons
Pros:
- +Excellent value for long-term supplementation
- +High dose for correcting deficiency
Cons:
- -May cause significant GI side effects
- -Constipation common at this dose
Iron Supplement Guide
Forms of Iron Explained
Ferrous Bisglycinate (Iron Bisglycinate)
Ferrous bisglycinate is chelated iron bound to glycine amino acids. Research published in the American Journal of Clinical Nutrition shows this form has high bioavailability with minimal gastrointestinal side effects. The chelation protects iron from inhibitors in food and allows absorption through a different pathway, reducing stomach upset and constipation common with other iron forms.
Ferrous Sulfate
Ferrous sulfate is the most commonly prescribed and studied iron supplement. It contains about 20% elemental iron by weight. While well-absorbed, ferrous sulfate commonly causes GI side effects including nausea, constipation, and stomach upset. Taking it on an empty stomach maximizes absorption but may worsen side effects.
Ferrous Fumarate
Ferrous fumarate contains about 33% elemental iron, making it more concentrated than ferrous sulfate. It has similar absorption but may cause fewer GI side effects in some individuals. Often used in prenatal vitamins.
Heme Iron
Heme iron is derived from animal hemoglobin and myoglobin. Research shows heme iron is absorbed 2-3 times more efficiently than non-heme iron and is less affected by dietary inhibitors like phytates, tannins, and calcium. Some supplements combine heme and non-heme iron for optimal absorption.
Carbonyl Iron
Carbonyl iron is pure elemental iron particles. It is absorbed more slowly than iron salts and is safer in case of accidental overdose, making it sometimes recommended for children's supplements. However, it may be less effective for quickly correcting deficiency.
Who Needs Iron Supplements
- •Women with heavy menstrual periods: Monthly blood loss can lead to iron deficiency
- •Pregnant women: Increased blood volume and fetal development increase iron needs significantly
- •Vegetarians and vegans: Plant-based iron is less bioavailable than meat-based iron
- •Endurance athletes: Increased iron losses through sweat, urine, and GI bleeding
- •People with malabsorption conditions: Celiac disease, inflammatory bowel disease, or gastric bypass
- •Those with diagnosed iron deficiency: Confirmed through blood work (low ferritin, low hemoglobin)
Dosage and Administration
Iron supplementation dosage depends on the severity of deficiency and should be determined by a healthcare provider based on blood work. Typical doses range from 25-65mg of elemental iron daily for mild deficiency, to 65-200mg daily in divided doses for more severe deficiency or anemia.
For best absorption, iron is typically taken on an empty stomach, though this may increase side effects. Taking iron with vitamin C enhances absorption, while calcium, dairy products, coffee, tea, and whole grains inhibit absorption. Space iron at least 2 hours apart from these foods and supplements.
Iron stores take time to replenish. Even after hemoglobin normalizes, ferritin (iron storage protein) may remain low and require continued supplementation for 3-6 months. Follow-up blood work is essential to monitor progress and prevent over-supplementation.
Managing Side Effects
Constipation is the most common side effect of iron supplementation, particularly with ferrous sulfate. Strategies to minimize this include starting with a lower dose and gradually increasing, taking iron with food (despite reduced absorption), increasing fluid and fiber intake, and considering a switch to ferrous bisglycinate or slow-release formulations.
Iron can cause dark or black stools, which is harmless but expected. Nausea can be reduced by taking iron with food or switching to a gentler form. If side effects persist despite these measures, consult your healthcare provider about alternative strategies.
Critical Safety Information
- •Iron poisoning: Accidental iron overdose is a leading cause of poisoning deaths in children under 6. Keep iron supplements locked away from children.
- •Hemochromatosis: People with this genetic disorder accumulate excess iron and must never take iron supplements.
- •Medication interactions: Iron reduces absorption of thyroid medications (levothyroxine), antibiotics (tetracyclines, quinolones), and bisphosphonates. Take iron at least 4 hours apart from these medications.
- •Proton pump inhibitors and antacids: These reduce stomach acid needed for iron absorption. May need higher doses or different forms.
- •Men and postmenopausal women: Should only supplement iron if diagnosed with deficiency. Excess iron is linked to increased oxidative stress and potential cardiovascular risk.
GET BLOOD WORK BEFORE SUPPLEMENTING
Iron supplementation should be based on demonstrated deficiency through blood tests including serum ferritin, complete blood count (CBC), and iron studies. Do not self-diagnose or self-treat with iron. Excess iron accumulates in organs and can cause serious health problems including liver damage, heart disease, and diabetes. Work with a healthcare provider to determine if you need iron, the appropriate dose, and to monitor your progress.
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