Quick Summary

Compare all iron supplement forms (ferrous bisglycinate, sulfate, citrate, fumarate). Find the best type for absorption, side effects, and cost based on your deficiency level.

Your ferritin came back at 18 ng/mL. Your doctor hands you a prescription: "Take iron." You buy a bottle. Three months later, your levels haven't budged-and your stomach has been miserable the entire time.

The problem isn't that you're not trying. It's that you chose the wrong form.

Different iron supplements cause dramatically different side effects. Ferrous sulfate (the cheap, common one) causes constipation and nausea so severe that 40-50% of people quit. Meanwhile, ferrous bisglycinate absorbs just as well with almost no GI issues. Same mineral, completely different experience.

This guide breaks down all six forms by absorption, tolerability, cost, and clinical evidence. By the end, you'll know exactly which iron to buy based on your deficiency severity and GI sensitivity.

Quick Decision Tree - Choose Your Iron in 30 Seconds

Start here what's your situation?

• Best absorption with minimal side effects? Ferrous bisglycinate 25-50mg daily (chelated, gentle)

• Severe deficiency needing fast correction? Ferrous sulfate 65mg elemental 2-3x daily (standard medical protocol)

• Sensitive stomach or IBS? Ferrous bisglycinate 25mg daily (least GI upset)

• On a tight budget? Ferrous sulfate 65mg daily (cheapest, but harsh on stomach)

• Moderate deficiency? Ferrous citrate 25mg or bisglycinate 25-50mg daily

• Vegan with absorption issues? Heme iron polypeptide 11mg daily (animal-derived, best absorption)

• Pregnancy/heavy periods? Ferrous bisglycinate 25-50mg daily (gentle, effective)

• Already tried sulfate and couldn't tolerate? Ferrous bisglycinate or iron polysaccharide

• Want food-based iron? Heme iron from liver, red meat, oysters (but won't correct severe deficiency alone)

Still not sure? Keep reading we'll break down exactly why these recommendations work.

The 6 Iron Forms - At-a-Glance Comparison

Here's what you need to know about each form before we dive deeper:

But there's a catch: Higher elemental iron percentage doesn't mean better. Ferrous sulfate has 20% elemental iron but causes such severe GI distress that people stop taking it. Ferrous bisglycinate has the same 20% but absorbs better with minimal side effects. What most people don't realize is that tolerability matters just as much as absorption.

Track Your Iron Levels

Mito Health tests 100+ biomarkers including serum iron, ferritin, transferrin saturation, TIBC, and hemoglobin with physician-guided protocols to help you optimize energy, prevent anemia, and identify the right iron form for you. Our comprehensive panels provide personalized interpretation to correct deficiency safely.

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• Cost per day: $0.05-0.10

• Annual cost: $20-35

• Best value if: Budget is extremely tight and you can tolerate GI side effects

Ferrous Bisglycinate:

• $15-30 per 90 capsules (25mg elemental)

• Cost per day: $0.15-0.35 (one capsule)

• Annual cost: $55-130

• Best value if: You want optimal absorption and minimal side effects (worth the 3x premium over sulfate)

Ferrous Fumarate:

• $8-15 per 100 tablets (106mg elemental)

• Cost per day: $0.08-0.15

• Annual cost: $30-55

Ferrous Citrate:

• $10-18 per 100 tablets (28mg elemental)

• Cost per day: $0.10-0.18

• Annual cost: $35-65

Heme Iron Polypeptide:

• $25-40 per 30 capsules (11mg)

• Cost per day: $0.80-1.30

• Annual cost: $300-475

• Best value if: You have malabsorption and other forms don't work (otherwise overpriced)

The value calculation:
Sulfate to Bisglycinate = 3x price increase but:

• 70-80% fewer side effects

• Better compliance (people actually take it)

• Potentially better absorption at lower doses

Is it worth it? Yes, for most people. If sulfate causes constipation so bad you stop taking it, you've wasted $20 and still have iron deficiency. Bisglycinate at $100/year that you actually take is better value.

Common Mistakes (And How to Avoid Them)

Mistake #1: Taking iron with coffee/tea/dairy

• The fix: Separate iron from calcium, tannins, phytates by 2+ hours. Take iron with vitamin C instead.

Mistake #2: Expecting instant results

• The fix: Energy improves in 2-4 weeks. Full ferritin correction takes 3-6 months. Blood work improves before symptoms.

Mistake #3: Stopping too soon

• The fix: Continue supplementation until ferritin is >50 ng/mL (ideally 50-100), then switch to maintenance dosing. Don't stop when you "feel better" at ferritin 30.

Mistake #4: Not testing ferritin (only testing hemoglobin)

• The fix: Hemoglobin normalizes before iron stores refill. Test ferritin to know when to stop intensive supplementation.

Mistake #5: Taking too much (more is not better)

• The fix: 25-50mg elemental daily is sufficient for most people. Doses >100mg don't absorb proportionally better and cause more GI distress.

Mistake #6: Not addressing underlying blood loss

• The fix: If ferritin won't rise despite supplementation, investigate: heavy periods, GI bleeding, frequent blood donation, parasites.

Mistake #7: Using ferrous sulfate when GI-sensitive

• The fix: If you have IBS, gastritis, or couldn't tolerate iron before, go straight to bisglycinate. Don't "try to push through."

Mistake #8: Taking iron with a proton pump inhibitor (PPI)

• The fix: PPIs reduce stomach acid needed for iron absorption. Take iron 2-3 hours before PPI, or ask doctor about tapering PPI.

Your Personalized Health Journey

Join Mito Health's annual membership to test 100+ biomarkers with concierge-level support from your care team. Track your iron, ferritin, and related biomarkers with repeat testing and personalized protocols.

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The Bottom Line - Your Iron Action Plan

If you're still overwhelmed, here's your decision flowchart:

For 70% of people: Start with ferrous bisglycinate 25mg daily (or 25mg x2 if deficient). It's the best balance of absorption, tolerability, and effectiveness. Give it 3-4 months before evaluating.

If you have severe deficiency (<15 ng/mL ferritin): Try ferrous sulfate 65mg 2x daily first (standard medical protocol, fastest correction). If you can't tolerate it after 1-2 weeks, switch to ferrous bisglycinate 25mg x2 daily.

If you're GI-sensitive (IBS, Crohn's, gastritis): Go straight to ferrous bisglycinate 18-25mg daily. Don't waste time trying sulfate it will make your symptoms worse.

If you're on a very tight budget: Ferrous sulfate 65mg daily works at $20-35/year. Take it with 100mg vitamin C and on a relatively empty stomach. If constipation becomes severe, try every-other-day dosing.

If you have malabsorption: Consider heme iron polypeptide 11-33mg daily. If oral iron of any form doesn't raise ferritin after 3 months, ask your doctor about IV iron infusions.

Key Takeaways

• Ferrous bisglycinate is the best all-around choice Chelated form absorbs 2-3x better than sulfate, causes 70-80% fewer GI side effects (25-50mg daily)

• Ferrous sulfate works but is harsh Standard medical protocol, effective and cheap ($20/year), but 40-50% can't tolerate constipation/nausea

• Take iron with vitamin C, not coffee/dairy 100-200mg vitamin C doubles absorption, separate from calcium/tannins by 2+ hours

• Target ferritin >50 ng/mL, not just hemoglobin Hemoglobin normalizes first, but iron stores must refill to prevent recurrence

• Expect 10-15 ng/mL ferritin increase per month Full correction takes 3-6 months depending on severity and absorption

• Every-other-day dosing may be as effective Recent research shows alternate-day iron reduces side effects without compromising efficacy

• Don't stop when you "feel better" Continue until ferritin >50, then switch to maintenance dosing (18-25mg 2-3x per week)

• If ferritin won't rise, investigate blood loss Heavy periods, GI bleeding, parasites, or malabsorption may be ongoing

• Severe malabsorption may need IV iron If oral forms don't work after 3 months, ferric carboxymaltose infusions bypass GI issues

Photo from Unsplash Your biology is unique some people correct deficiency in 2 months, others need 6 months. Testing is the only way to know. Optimize from within.

Medical Disclaimer

This article is for educational and informational purposes only and does not constitute medical advice. The information provided should not be used for diagnosing or treating a health condition. Always consult with your doctor or qualified healthcare provider before starting any new supplement protocol, making changes to your diet, or if you have questions about a medical condition.

Individual results may vary. The dosages and protocols discussed are evidence-based but should be personalized under medical supervision, especially if you have existing health conditions or take medications.

Track Your Progress

• How to Improve Your Iron Level Naturally

• How to Improve Your Iron Saturation Level Naturally

• Total Iron Binding Capacity (TIBC)

• Iron

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References

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[2] 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. PMID: 29032957

[3] Pineda O, Ashmead HD. Effectiveness of treatment of iron-deficiency anemia in infants and young children with ferrous bis-glycinate chelate. Nutrition. 2001;17(5):381-384. PMID: 11377130

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[6] Gereklioglu C, et al. Medication adherence to oral iron therapy in patients with iron deficiency anemia. Pak J Med Sci. 2016;32(3):604-607. PMID: 27375697

[7] Hallberg L, Hulthén L. Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron. Am J Clin Nutr. 2000;71(5):1147-1160. PMID: 10799377

[8] Camaschella C. Iron deficiency. Blood. 2019;133(1):30-39. PMID: 30401705

[9] Lopez A, Cacoub P, Macdougall IC, Peyrin-Biroulet L. Iron deficiency anaemia. Lancet. 2016;387(10021):907-916. PMID: 26314490

[10] Pasricha SR, et al. Iron supplementation benefits physical performance in women of reproductive age: a systematic review and meta-analysis. J Nutr. 2014;144(6):906-914. PMID: 24717368