Iron Bisglycinate: Why It's the Best Iron Form and How to Choose
Iron deficiency is the most common nutritional deficiency worldwide: according to WHO, it affects about 2 billion people. In Estonia, according to Tervise Arengu Instituut, low ferritin levels are found in one out of three women of reproductive age. But classic iron supplements (sulfate, fumarate) cause nausea, constipation, and metallic taste, leading people to abandon treatment.
Iron bisglycinate solves this problem. This article covers everything you need to make an informed choice.
Who This Article Is For
This guide is for anyone facing iron deficiency or suspecting it: persistent fatigue, hair loss, brittle nails, pallor. Especially relevant for women, vegetarians, athletes, and blood donors. After reading, you'll know which iron form to choose and how to take it without side effects.
TL;DR: Key Takeaways
- Iron bisglycinate is a chelated form where iron is bound to two glycine molecules
- Absorbs 3-4x better than iron sulfate (Pineda & Ashmead, 2001)
- Minimal GI side effects — no constipation or nausea
- Optimal dosage: 25-50 mg elemental iron daily
- Take with vitamin C for maximum absorption
- Don't take with calcium, coffee, or tea — they block absorption
Why Bisglycinate, Not Regular Iron?
The problem with classic iron forms is how they absorb. Iron sulfate (FeSO4) enters the intestine as a free Fe2+ ion, which:
- Irritates the intestinal lining
- Competes with calcium, zinc, and magnesium for transporters
- Oxidizes to Fe3+, which is barely absorbed
- Causes constipation in 30-50% of users
Iron bisglycinate (Fe(C2H4NO2)2) is a chelated form where the iron atom is "wrapped" in two glycine amino acid molecules. This shell:
- Protects iron from oxidation in the intestine
- Enables absorption via amino acid channels, bypassing competition with other minerals
- Doesn't irritate the lining — iron doesn't contact the intestinal wall directly
- Doesn't react with phytates and tannins from food
Iron Forms Compared
| Form | Bioavailability | Side Effects | Price |
|---|---|---|---|
| Bisglycinate | High (~45%) | Minimal | Medium |
| Sulfate | Medium (~10-15%) | Constipation, nausea, dark stool | Low |
| Fumarate | Medium (~15%) | Constipation, abdominal pain | Low |
| Gluconate | Low (~8%) | Moderate | Low |
| Carbonyl | High (~25%) | Minimal | Medium |
| Liposomal | Very high (~50%) | Minimal | High |
Bottom line: Bisglycinate offers the best balance of bioavailability, tolerability, and price.
Who Needs Iron Bisglycinate
High-Risk Groups:
1. Women of reproductive age — monthly blood loss increases needs by 50%
2. Pregnant women — iron needs double (27 mg/day vs 18 mg/day)
3. Vegetarians and vegans — non-heme iron from plants absorbs 5-10x worse than heme iron
4. Endurance athletes — running destroys red blood cells (foot-strike hemolysis), losses through sweat
5. Blood donors — each donation removes ~250 mg iron
6. Adolescents during growth spurts — needs increase by 30%
How to Know If You're Deficient
Iron deficiency symptoms develop gradually:
- Stage 1 (depleted stores): ferritin <30 mcg/L, may have no symptoms
- Stage 2 (latent deficiency): ferritin <15 mcg/L, fatigue, reduced performance
- Stage 3 (anemia): hemoglobin <120 g/L (women) / <130 g/L (men), shortness of breath, pallor, hair loss
Important: Don't take iron without a blood test. Excess iron is toxic. Get at least ferritin and a complete blood count.
Step-by-Step Protocol
1. Get a blood test — ferritin, serum iron, TIBC, hemoglobin
2. Determine dose by ferritin level:
- Ferritin 15-30: 25 mg elemental iron every other day
- Ferritin <15: 25-50 mg daily
- Anemia: as prescribed by doctor, usually 50-100 mg
3. Take on empty stomach (30 min before meals) or with a light snack containing vitamin C
4. Add vitamin C — 200 mg ascorbic acid increases iron absorption 2-3x
5. Don't combine with dairy, coffee, tea, calcium (separate by 2-3 hours)
6. Follow-up test in 8-12 weeks — ferritin should rise 15-25 mcg/L per month
7. After normalization — continue maintenance dose (25 mg every other day) for another 3-6 months
New Approach: Every-Other-Day Dosing
A study by Stoffel et al. (2017), published in The Lancet Haematology, revolutionized recommendations: every-other-day dosing proved more effective than daily. The reason — hepcidin, a hormone produced after iron intake that blocks absorption for 24 hours. With every-other-day dosing, hepcidin has time to decrease, and the next dose is fully absorbed.
What to Look For When Choosing
- Elemental iron content — look for 25-36 mg per capsule
- Additional components — vitamin C, folic acid (especially for pregnant women)
- Form — capsules preferred over tablets (less mucosal contact)
- No unnecessary additives — avoid iron oxide as a colorant
Browse quality iron supplements: iron and minerals at MaxFit.ee.
Common Mistakes
1. Taking iron with coffee — Tannins in coffee and tea reduce iron absorption by 60-90%. Wait at least 2 hours after taking iron.
2. Combining with calcium — Calcium blocks iron absorption. If taking both, separate by 3+ hours.
3. Taking too much — Daily doses above 45 mg elemental iron can cause side effects even with bisglycinate. More is not better.
4. Stopping after feeling better — Hemoglobin recovers in 2-3 months, but ferritin stores take 6-12 months. Complete the full course.
5. Not checking ferritin — Without testing, you can't determine the right dose or track progress.
Iron Bisglycinate and Sport
Iron deficiency is a leading cause of unexplained performance decline. Burden et al. (2015) showed that 35% of female runners have ferritin below 30 mcg/L, and 5% have true anemia.
Iron is essential for:
- Oxygen transport (hemoglobin and myoglobin)
- Energy metabolism (cytochromes)
- Neurotransmitter synthesis (dopamine, serotonin)
Recommendation for athletes: Check ferritin every 6 months. Target level is above 50 mcg/L for optimal performance (Peeling et al., 2007).
Absorption Enhancers and Blockers
Enhance (take together):
- Vitamin C — increases absorption 2-3x
- Meat and fish — MFP factor stimulates non-heme iron absorption
- B vitamins — B12 and folic acid are essential for blood formation
Block (separate 2-3 hours):
- Calcium — direct competition for transporters
- Coffee and tea — tannins bind iron
- Dairy — casein reduces absorption
- Phytates (whole grains, legumes) — form insoluble complexes
- Zinc — competes for DMT-1 transporter
Can You Take Iron Bisglycinate During Pregnancy?
Yes, iron bisglycinate is considered one of the best forms for pregnant women. Milman et al. (2014) showed that chelated iron effectively raises ferritin with significantly fewer side effects (8% vs 30% for sulfate). This is critical since iron-induced nausea worsens first-trimester morning sickness.
Dosage during pregnancy is determined by your doctor — usually 30-60 mg elemental iron daily.
How Long Until Iron Bisglycinate Works?
First improvements (energy, reduced fatigue) are usually noticeable within 2-3 weeks. Hemoglobin starts rising at 4-6 weeks. Full ferritin normalization takes 3-6 months depending on deficiency severity.
Can You Take Iron Bisglycinate with Magnesium?
Yes, with a caveat. Magnesium and iron compete for intestinal transporters. Optimal schedule: iron in the morning on an empty stomach with vitamin C, magnesium (e.g., magnesium glycinate) in the evening before bed. This separation ensures maximum absorption of both minerals.
Does Iron Bisglycinate Cause Constipation?
Unlike iron sulfate and fumarate, bisglycinate very rarely causes constipation. This is one of the main advantages of the chelated form. A meta-analysis by Name et al. (2018) in Current Developments in Nutrition confirmed that GI side effects with bisglycinate are 3-4x lower than sulfate.
If constipation does occur, add magnesium citrate — it has a mild laxative effect and complements iron supplementation.
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