Iron Bisglycinate
SupplementThe small divergence indicates good agreement between clinical evidence [s1, s2] and community experiences [c1, c2]. Users confirm the improved tolerability observed in RCTs; slight advantage in the community score driven by strong personal experiences compared to ferrous sulfate.
Unlock full information
Dosages, side effects, studies and more — free after registration.
Register for freeRating Scales
TL;DR
Iron bisglycinate is a chelated iron form absorbed via two intestinal pathways (DMT1 and PepT1), resulting in significantly higher bioavailability compared to inorganic iron salts. The dual absorption route, particularly the intact chelate uptake via PepT1, explains its superior gastrointestinal tolerability. It is effective for the prevention and treatment of iron deficiency and iron deficiency anemia with a low risk profile.
Description
Chelated iron form with high bioavailability and good gastrointestinal tolerability for the prevention and treatment of iron deficiency [s1, s2].
Iron bisglycinate (also: ferrous bisglycinate) is a chelated iron compound in which a divalent iron(II) ion is bound to two molecules of the amino acid glycine. The chemical formula is C₄H₈FeN₂O₄ [s3]. This ring structure protects the iron during gastric passage and enables absorption via the peptide transporter PepT1 in the small intestine, which is also responsible for dipeptides and oligopeptides [s4, s5]. Compared to inorganic iron salts such as ferrous sulfate, iron bisglycinate demonstrates superior bioavailability and significantly fewer gastrointestinal side effects such as nausea, constipation, and stomach pain in clinical studies [s1, s2]. A meta-analysis of RCTs found that iron bisglycinate was more effective than other iron salts in pregnant women, but showed comparable efficacy in children [s1]. Iron is essential for the formation of hemoglobin and myoglobin, oxygen transport, and numerous enzymatic processes. Daily iron requirements are approximately 10 mg for men, approximately 15 mg for premenopausal women, and up to 27–30 mg daily during pregnancy [s6, s7]. High-risk groups for iron deficiency include pregnant women, women with heavy menstruation, children in growth phases, and individuals with chronic intestinal diseases. The chelated form offers the advantage over ferrous sulfate that absorption is less strongly inhibited by dietary components such as phytates, polyphenols, or calcium [s5]. Therapeutically, doses of 60–120 mg elemental iron per day are used in iron deficiency anemia; 25 mg iron as bisglycinate has been described in studies as equally effective as 50 mg ferrous sulfate [s1, s7].
Legal Status (DE)
In the DACH countries, iron bisglycinate is marketable as an over-the-counter dietary supplement. The BfR has issued maximum quantity recommendations for iron in dietary supplements and advises against taking iron preparations without a medical diagnosis [s10, s11]. In 2024, EFSA established a tolerable upper intake level for iron from all sources of 40 mg/day for adults [s9].
Mechanism of Action
Iron bisglycinate is absorbed in the small intestine via two pathways: first, via the classical DMT1 transporter (Divalent Metal Transporter 1) following dissociation of the chelate, and second — and this is the key difference from inorganic iron salts — via the peptide transporter PepT1, which recognizes and absorbs the intact chelate as a dipeptide analogue [s4, s5]. This second absorption pathway enables uptake that is largely independent of dietary inhibitors (phytates, tannins, calcium) [s5]. Following absorption, iron(II) is partly stored in the mucosal cell (as ferritin) and partly released into the blood via ferroportin, where it is transported bound to transferrin. The hormone hepcidin regulates iron release from enterocytes and macrophages and adjusts absorption to the body's requirements [s4]. In the body, iron is indispensable for: hemoglobin (oxygen transport in erythrocytes), myoglobin (oxygen storage in muscles), cytochrome enzymes of the respiratory chain, and the synthesis of neurotransmitters such as dopamine and serotonin [s6]. The glycine binding protects the iron ion from oxidative inactivation in the stomach and reduces direct contact with the gastric mucosa, which explains the significantly better gastrointestinal tolerability compared to ferrous sulfate [s2, s3].
Dosing
Prävention Eisenmangel (Erwachsene Frauen)
- Dose
- 14–18 mg elemental iron
- Frequency
- 1× täglich
- Route
- oral
- Duration
- fortlaufend
- Timing
- Fasted or with a vitamin C-containing beverage for better absorption
- With food
- optional
Eisenmangelanämie Therapie (Erwachsene)
- Dose
- 60–120 mg elemental iron
- Frequency
- 1–2× täglich
- Route
- oral
- Duration
- 3–6 Monate oder bis Ferritin normalisiert
- Timing
- Fasted, at least 1–2 hours apart from calcium, coffee, tea
- With food
- optional
Eisenprophylaxe in der Schwangerschaft
- Dose
- 25–30 mg elemental iron as bisglycinate
- Frequency
- 1× täglich
- Route
- oral
- Duration
- Ab 2. Trimester bis Wochenbett
- Timing
- Fasted or between meals
- With food
- optional
Eisenmangel bei Kindern (6–12 Jahre)
- Dose
- 2–3 mg/kg body weight elemental iron, max. 40 mg/day
- Frequency
- 1× täglich
- Route
- oral
- Duration
- 3 Monate, dann Kontrolle
- Timing
- Between meals
- With food
- optional
EFSA (2024) recommends a tolerable upper intake level of 40 mg elemental iron per day from all sources for adults (including pregnant and breastfeeding women) and a maximum of 35 mg/day for adolescents (15–17 years) [s9]. The BfR recommends taking iron-containing dietary supplements only in cases of confirmed deficiency [s10, s11].
Do not take iron simultaneously with calcium, coffee, black tea, phytates (whole grain products), or certain antibiotics. Vitamin C (50–100 mg) improves absorption. Black discoloration of stools is a normal and harmless phenomenon [s8].
Side Effects
| Side Effect | Frequency | Severity |
|---|---|---|
| Schwarze Stuhlverfärbung Normal phenomenon due to unabsorbed iron in the intestine; not clinically significant [s8]. | häufig | leicht |
| Gastrointestinale Beschwerden (Übelkeit, Magenschmerzen, Verstopfung) Significantly less frequent than with iron sulfate; reduced with bisglycinate due to PepT1 absorption and gastric mucosal protection [s1, s2, s3]. | gelegentlich | leicht |
| Durchfall oder weicher Stuhl Possible especially at higher doses (>60 mg/day elemental iron) [s8]. | gelegentlich | leicht |
| Sodbrennen oder Reflux Individual community case reports; less common than with ferrous sulfate, but possible [c1]. | selten | leicht |
| Eisenüberladung (Hämochromatose-Risiko) In genetic hemochromatosis or long-term overdosing without confirmed deficiency; potentially organ-damaging (liver, heart) [s9, s10]. | selten | schwer |
| Akute Eisenvergiftung (Überdosierung) Accidental ingestion of high doses, particularly dangerous for children under 6 years of age; can be fatal [s8, s9]. | selten | schwer |
Contraindications
Uncontrolled iron accumulation with organ damage to liver, heart, and pancreas. Absolute contraindication for iron supplementation without medical supervision [s9, s10].
Iron administration in the setting of increased hemolytic turnover can lead to dangerous iron overload [s9].
Oral iron may exacerbate intestinal inflammation; parenteral iron administration preferred during active flare [s9].
High risk of accidental iron poisoning; store iron preparations safely and use only under medical supervision [s8].
Additional iron intake worsens overload and increases oxidative stress [s9, s10].
Interactions
Synergistic
Vitamin C (ascorbic acid) substantially improves non-heme iron absorption by reducing Fe³⁺ to the more readily absorbed Fe²⁺. Many iron bisglycinate products contain vitamin C as a fixed component. The combination is particularly recommended with plant-based iron sources.
Caution
Quercetin, as a potent iron-chelating polyphenol, inhibits intestinal non-heme iron absorption and downregulates iron metabolism genes. Maintain a gap of at least 1–2 hours between quercetin and iron intake.
Calcium at doses of 300–600 mg can significantly reduce non-heme iron absorption. Calcium and iron supplements should be taken at separate times. Take iron in the morning and calcium with a different meal.
Magnesium salts may impair intestinal iron absorption, as both minerals compete for similar transport pathways. A time interval of at least 1–2 hours between intake is recommended.
High iron doses can interfere with intestinal copper absorption, as both trace elements compete for the same uptake mechanism. A time interval between supplementation is advisable when taken concurrently.
Polyphenols such as EGCG from green tea inhibit intestinal non-heme iron absorption. Green tea or green tea extracts should not be taken simultaneously with iron supplements. A gap of at least 1–2 hours is advisable.
Iron, as a polyvalent cation, can impair the absorption of L-thyroxine when thyroid hormones are taken together with iodine-containing preparations. In patients on thyroid medication, iron should be taken at a separate time (≥ 2 hours apart).
Studies
Tier A — High Evidence
Outcome: Hemoglobin and ferritin concentrations; gastrointestinal adverse effects
Effect Size: Significant superiority over other iron salts for Hb (SMD=0.49) in pregnant women; comparable efficacy in children. Fewer GI events in the bisglycinate group.
Outcome: Hemoglobin and ferritin levels; gastrointestinal tolerability
Effect Size: 25 mg iron as bisglycinate equivalent to 50 mg ferrous sulfate with significantly fewer gastrointestinal adverse effects in the bisglycinate group.
Tier B — Moderate Evidence
Outcome: Intestinal absorption and metabolism of iron amino acid chelates
Effect Size: Significantly increased absorption from chelates vs. inorganic salts; mucosal regulatory mechanism demonstrated.
Outcome: Mechanism of iron absorption from amino acid chelates
Effect Size: Evidence of PepT1-mediated absorption; less inhibition by dietary inhibitors than ferrous sulfate.
Tier C — Low Evidence
Outcome: Bioavailability and gastrointestinal tolerability of various iron forms
Effect Size: Ferrous bisglycinate showed better tolerability and comparable bioavailability compared to FeSO₄ in an animal model.
Community Evidence
Top reported benefits
- Significantly better gastrointestinal tolerability than iron sulfate
- Rapid improvement of ferritin and hemoglobin levels
- No or minimal constipation issues
- Increased energy and reduction of fatigue symptoms after 2–4 weeks
- Can be taken on an empty stomach without issues
Top reported issues
- Occasional bloating or mild reflux in some users
- No noticeable energy improvement in some users despite rising ferritin levels
- Higher price compared to ferrous sulfate preparations
- Black stool discoloration concerns some users (although harmless)
Isolated reports of persistent fatigue despite 6 months of use; in these cases, other causes (B12 deficiency, thyroid function) should be investigated [c1]. Stiftung Warentest classifies many OTC iron preparations as "of little benefit" as they exceed BfR maximum quantity recommendations [s11]. Self-medication without iron status diagnostics is viewed critically by experts [s10, s11].
Scientific Sources
- The effects of oral ferrous bisglycinate supplementation on hemoglobin and ferritin concentrations in adults and children: a systematic review and meta-analysis of randomized controlled trials
Cepeda M, Chacón-Labella J, Moran-Llorente V, et al. (2023). American Journal of Clinical NutritionAPMID:36728680DOI - Verwendung von Eisen in Nahrungsergänzungsmitteln und zur Anreicherung von Lebensmitteln
Bundesinstitut für Risikobewertung (BfR) (2022). BfR-StellungnahmeALink - Stiftung Warentest: Eisen-Präparate nicht in Eigenregie nehmen
Pharmazeutische Zeitung / Stiftung Warentest (2023). Pharmazeutische ZeitungBLink - Comparative study of the effects of different iron sources on bioavailability and gastrointestinal tolerability in iron-deficient rats
Authors not individually specified in search results (2025). Scientific ReportsCDOI - Effect of supplementation with ferrous sulfate or iron bis-glycinate chelate on ferritin concentration in Mexican schoolchildren: a randomized controlled trial
Pineda O, Ashmead HD, Lemus CP, et al. (2014). Nutrition JournalALink - Low-dose ferrous bisglycinate chelate supplementation in chronic kidney disease and hemodialysis patients
Authors not individually specified in search results (2022). Journal of the Chinese Medical AssociationBLink - Iron Transport from Ferrous Bisglycinate and Ferrous Sulfate in DMT1-Knockout Human Intestinal Caco-2 Cells
Pizarro F, Olivares M, Arredondo M, Gaitán D, Mackenzie GG, Flores S, Lönnerdal B (2019). NutrientsCLink - Multicenter randomized double-blind trial: ferrous bisglycinate 25 mg vs. ferrous sulfate 50 mg in pregnant women with latent iron deficiency
Not individually identified in search results (2025). Not specified (reported via NahrungsHub)ALink - Ferrous Bisglycinate: USP, Application & Industrial Uses
WBCIL Editorial Team (2024). WBCIL Technical ResourcesCLink - The absorption and metabolism of iron amino acid chelate
Ashmead HD (2001). Archivos Latinoamericanos de NutricionBPMID:11688075 - Iron Amino Acid Chelates
Pineda O, Ashmead HD, Perez JM, et al. (2005). International Journal for Vitamin and Nutrition ResearchBPMID:15743019 - The absorption and metabolism of iron amino acid chelate
Ashmead HD (2001). Archivos Latinoamericanos de Nutricion / SciELOBLink - Ferrous bisglycinate 25 mg iron is as effective as ferrous sulfate 50 mg iron in the prophylaxis of iron deficiency and anemia during pregnancy in a randomized trial
Milman N, Jønsson L, Dyre P, et al. (2014). Journal of Perinatal MedicineADOI - Iron Supplements (Ferosul, Slow Fe, and others): Uses, Side Effects, Interactions – Drug Information
WebMD Medical Editorial Team (2024). WebMD Drug ReferenceCLink - Scientific opinion on the tolerable upper intake level for iron
EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) (2024). EFSA JournalAPMID:38868106DOI
Community Sources
Storage
Unopened
Store in a dry, cool place (below 25°C), protected from light.
Opened
Keep container tightly closed; protect from moisture.
Notes
Store iron preparations safely and out of reach of children. Accidental overdose in young children can be life-threatening [s8].