Iron Bisglycinate

Iron bisglycinate (ferrous bisglycinate) is elemental iron chelated to two molecules of the amino acid glycine — a form marketed for good absorption and better gut tolerance than the older ferrous salts (sulfate, fumarate, gluconate). For iron’s full evidence base — deficiency anaemia, intake references, and the “don’t take it without a diagnosed need” framing — see Iron; this page covers what’s specific to the bisglycinate form.

Absorption & Tolerability

The headline claim for chelated iron is superior bioavailability, and it is overstated. A stable-isotope competition study in 85 women showed that iron bis-glycine chelate is absorbed through the classic nonheme-iron pathway — it competes directly with ferrous sulfate for the same intestinal transporter (DMT1) rather than using a privileged “amino-acid” route, and the two share a common absorptive pool ^{1Reference 1Pizarro et al. · 2002RCTIron bis-glycine chelate competes for the nonheme-iron absorption pathway — randomized human absorption studyView study →}. In practice the chelate is well absorbed, and the glycine shell protects the iron from dietary inhibitors (phytate, polyphenols, calcium) and buffers it against gastric interactions — but at nutritional doses the absorption advantage over sulfate is modest, not dramatic ^{2Reference 2Ashmead · 2001ReviewThe absorption and metabolism of iron amino acid chelate — reviewView study →}.

The form’s genuine, repeatable advantage is gut tolerability. Because the iron is shielded by glycine, less reactive free ferrous iron is released in the stomach and gut lumen, which is the mechanistic basis for fewer complaints of nausea, epigastric pain, constipation, and black stools. In a head-to-head of three equipotent prophylactic formulas in pregnancy, ferrous bisglycinate 25 mg had the most favourable GI profile and the lowest rate of black stools (8%, vs 22% for fumarate 40 mg and 31% for sulfate 50 mg) ^{3Reference 3Milman et al. · 2024RCTLow-dose prophylactic oral iron in pregnancy is not associated with clinically significant GI complaints (ferrous fumarate vs bisglycinate vs sulphate) — two randomized studiesView study →}. That tolerability edge is the real reason to reach for it: it is the form to switch to when ferrous sulfate causes GI upset, and better tolerance tends to improve adherence — which is what ultimately determines whether a course of iron works.

Elemental iron content is ~20% of the chelate mass and varies by product, so dose by the elemental figure on the label, not the compound weight.

What the Evidence Says

Most large iron trials used ferrous sulfate, so bisglycinate-specific outcome data are more limited — but the form has now been tested in several randomised trials and one meta-analysis, and the picture is consistent with its mechanism: comparable efficacy at equivalent or lower elemental doses, with fewer GI side effects — in the right population.

• Meta-analysis (the anchor). A 2023 systematic review and meta-analysis of 17 RCTs found that in pregnant women, ferrous bisglycinate produced higher haemoglobin than comparator iron supplements (standardised mean difference 0.54 g/dL; 95% CI 0.15–0.94) and roughly a two-thirds reduction in GI adverse events (incidence rate ratio 0.36; 95% CI 0.17–0.76). Ferritin showed a non-significant trend in the same direction, and no significant benefit was seen in children; the authors called for more trials in non-pregnant adults ^{4Reference 4Fischer et al. · 2023Meta-analysisEffects of oral ferrous bisglycinate on hemoglobin and ferritin in adults and children — systematic review and meta-analysis of RCTsView study →}.
• Prophylaxis in pregnancy. A double-blind Danish RCT found ferrous bisglycinate at 25 mg elemental iron/day was non-inferior to ferrous sulfate at 50 mg/day for preventing iron deficiency and anaemia, with significantly fewer GI complaints (P=0.001) — i.e., the same protection at half the elemental dose and better tolerance ^{5Reference 5Milman et al. · 2014RCTFerrous bisglycinate 25 mg iron is as effective as ferrous sulfate 50 mg iron in the prophylaxis of iron deficiency and anemia during pregnancy — randomized trialView study →}. A 2022 RCT in iron-deficient pregnant women reported that bisglycinate (24 mg) with folinic acid raised early serum iron more than a higher dose of ferrous fumarate (66 mg) with fewer side effects ^{6Reference 6Bumrungpert et al. · 2022RCTEfficacy and safety of ferrous bisglycinate and folinic acid in the control of iron deficiency in pregnant women — randomized controlled trialView study →}.
• The important caveat — dose and population matter. In a rigorous noninferiority RCT in Cambodian women (largely iron-replete), a low 18 mg bisglycinate dose was NOT non-inferior to 60 mg ferrous sulfate for raising ferritin over 12 weeks (adjusted difference 14.6 µg/L favouring sulfate) ^{7Reference 7Fischer et al. · 2023RCTIs 18-mg ferrous bisglycinate noninferior to 60-mg ferrous sulfate in increasing ferritin while reducing gut inflammation? A randomized noninferiority trial in Cambodian womenView study →}. The lesson is not that bisglycinate is ineffective, but that a small elemental dose of a well-absorbed form cannot substitute for a much larger elemental dose when the total iron delivered is what matters — and that the tolerability rationale is weakest where there is no deficiency to correct.
• Repletion in deficiency. In iron-deficient (non-anaemic) Mexican schoolchildren, both bisglycinate and ferrous sulfate raised ferritin; there was no difference between the forms at one week, but by 6 months ferritin was higher in the bisglycinate group ^{8Reference 8Duque et al. · 2014RCTEffect of supplementation with ferrous sulfate or iron bis-glycinate chelate on ferritin concentration in Mexican schoolchildren — randomized controlled trialView study →}. A small RCT in cancer patients with mild iron-deficiency anaemia found bisglycinate at a lower elemental dose achieved comparable haemoglobin and ferritin recovery to a higher dose of ferrous sulfate with less toxicity (n=24, exploratory) ^{9Reference 9Ferrari et al. · 2012RCTTreatment of mild non-chemotherapy-induced iron deficiency anemia in cancer patients: ferrous bisglycinate chelate vs ferrous sulfate — randomized comparisonView study →}. Bisglycinate has also been used as an oral add-on to intravenous iron for postpartum anaemia ^{10Reference 10Yefet et al. · 2021RCTAddition of oral iron bisglycinate to intravenous iron sucrose for treatment of postpartum anemia — randomized controlled trialView study →}.

The honest read for this form: the evidence supports bisglycinate as a well-tolerated, efficacy-equivalent alternative to ferrous sulfate at matched or modestly lower elemental doses, with its clearest, best-replicated advantage being fewer GI side effects in pregnancy. Claims of a large absorption superiority are not well supported — it shares the nonheme pathway with the cheaper salts. Choose it for tolerance and adherence, not for a bioavailability miracle, and dose it by elemental iron against a diagnosed need. For iron’s full evidence base across all applications, see the Iron hub.

Dosage

Dosed as elemental iron, and — unlike most supplements — iron dosing should follow a diagnosed deficiency and clinician guidance, not routine use. Because ~20% of the chelate is elemental iron, read the elemental figure on the label. Studied prophylactic doses are around 18–25 mg elemental iron/day; therapeutic repletion uses higher clinician-directed doses. Fractional absorption falls as the dose rises and alternate-day or once-daily (rather than divided) dosing can improve net uptake — see the Iron hub for intake references (RDA 8–27 mg/day depending on age/pregnancy; UL 45 mg/day elemental). Doses studied in research, not a personal recommendation.

Safety

Ferrous bisglycinate is gentler on the gut than the older salts but carries the same core iron cautions — do not supplement iron without a diagnosed need. A formal safety evaluation (Ferrochel) reported an oral LD50 of 2800 mg/kg in rats and a no-observed-adverse-effect level of 500 mg/kg body weight/day (the highest dose tested), with iron amino-acid chelates judged appropriately safe as fortificants and supplements at intended intakes ^{11,12Reference 11Jeppsen et al. · 1999AnimalSafety evaluation of ferrous bisglycinate chelate (Ferrochel) — NOAEL 500 mg/kg/day, ratView study →Reference 12Jeppsen · 2001ReviewToxicology and safety of Ferrochel and other iron amino acid chelates — reviewView study →}. The chelate’s better tolerability does not make it safer in overdose: acute iron overdose is dangerous and a leading cause of fatal poisoning in young children — keep all iron products away from children. General iron cautions and drug interactions (see below and the Iron hub) apply to this form.

Pregnancy & lactation

Verdict: appropriate when iron deficiency is diagnosed in pregnancy, and among the better-tolerated options. The strongest bisglycinate evidence is in pregnant women, where it matches or exceeds other oral iron for haemoglobin response with fewer GI complaints ^{4,5,6Reference 4Fischer et al. · 2023Meta-analysisEffects of oral ferrous bisglycinate on hemoglobin and ferritin in adults and children — systematic review and meta-analysis of RCTsView study →Reference 5Milman et al. · 2014RCTFerrous bisglycinate 25 mg iron is as effective as ferrous sulfate 50 mg iron in the prophylaxis of iron deficiency and anemia during pregnancy — randomized trialView study →Reference 6Bumrungpert et al. · 2022RCTEfficacy and safety of ferrous bisglycinate and folinic acid in the control of iron deficiency in pregnant women — randomized controlled trialView study →}. This is not licence for untargeted use — iron in pregnancy should still be guided by iron status and antenatal care, as on the Iron hub.

Scope disclosure (honesty — not a claim):

• Interactions assessed? Partially. Iron absorption is reduced by, and can reduce absorption of, several drug classes — tetracycline/fluoroquinolone antibiotics, levothyroxine, bisphosphonates, methyldopa, penicillamine, and levodopa — and by antacids/proton-pump inhibitors, calcium, and polyphenol-rich foods/tea; separate dosing by ≥2 hours. Full interaction detail lives on the Iron hub; form-specific interaction studies for bisglycinate are limited.
• Pregnancy/lactation assessed? Yes — summarised above; the bisglycinate evidence base is strongest in pregnancy.
• Upper Limit (UL) established? Yes — 45 mg/day elemental iron for adults (IOM), counting supplemental iron; this applies to the elemental iron in the chelate, not the compound weight. Never infer that higher is safe from the absence of reports.

Absence of form-specific reports is not evidence of safety. Where bisglycinate has not been studied separately (e.g., most drug interactions), the mineral-level iron cautions on the hub apply.

Related compounds / cross-links

• Hub: Iron — the nutrient and its full, form-agnostic evidence base.
• Sibling forms: Ferrous sulfate, Ferrous fumarate, Ferrous gluconate.
• Cofactor for absorption: Vitamin C (enhances nonheme-iron uptake).

References

Last checked: July 2026.