What is ferrous bisglycinate?

What is Ferrous Bisglycinate

Ferrous bisglycinate is an amino acid iron chelate formulation that provides elemental iron for oral supplementation, typically containing 25 mg of elemental iron per tablet, and is recognized as one of the common oral iron preparations used to treat and prevent iron deficiency anemia. 1

Chemical Structure and Formulation

Ferrous bisglycinate is a chelated iron compound in which ferrous iron (Fe²⁺) is bound to two glycine molecules, creating a stable amino acid chelate complex. 2 This molecular structure differs fundamentally from traditional iron salts such as ferrous sulfate, ferrous fumarate, and ferrous gluconate. 1

Available Formulations and Dosing

• Standard elemental iron content: Approximately 25 mg of elemental iron per tablet 1
• Available forms: Tablet, capsule, and liquid formulations 1
• Cost: Approximately $2.40 for 30 pills, making it moderately priced compared to ferrous sulfate ($0.30-$4.50) but less expensive than polysaccharide-iron complex ($4.20) 1

Mechanism and Bioavailability

Ferrous bisglycinate demonstrates superior bioavailability compared to traditional iron salts, with apparent iron absorption rates reaching 90.9% versus 26.7% for ferrous sulfate in head-to-head studies. 3 The chelated structure allows the iron to remain stable through the acidic gastric environment and be absorbed intact in the small intestine, which explains both its enhanced bioavailability and reduced gastrointestinal side effects. 2

Clinical Efficacy

In Pregnant Women

• Ferrous bisglycinate 25 mg iron daily is as effective as ferrous sulfate 50 mg iron daily in preventing iron deficiency and iron deficiency anemia during pregnancy, demonstrating that half the dose of elemental iron achieves equivalent outcomes. 4
• Supplementation with ferrous bisglycinate for 4-20 weeks results in higher hemoglobin concentrations compared to other iron supplements (standardized mean difference 0.54 g/dL, P < 0.01). 2
• More than 95% of Danish women maintained adequate iron status during pregnancy and postpartum with only 25 mg iron daily as ferrous bisglycinate. 4

In Children and Infants

• In infants aged 6-36 months with iron deficiency anemia, ferrous bisglycinate at 5 mg/kg/day produced significant increases in both hemoglobin (P < 0.001) and plasma ferritin (P < 0.005), whereas ferrous sulfate increased hemoglobin but not ferritin significantly. 3
• Meta-analysis of pediatric trials showed no significant differences in hemoglobin or ferritin concentrations between ferrous bisglycinate and other iron supplements, though the evidence base is limited. 2

In Cancer Patients

• In cancer patients with mild non-chemotherapy-induced iron deficiency anemia, ferrous bisglycinate 28 mg daily for 20 days followed by 14 mg daily for 40 days achieved similar efficacy to ferrous sulfate 105 mg daily, with hemoglobin increasing from 11.6 to 13.0 g/dL (P = 0.0003) and ferritin from 16.1 to 33.8 ng/mL (P = 0.020). 5

Gastrointestinal Tolerability Advantage

Ferrous bisglycinate is associated with significantly fewer gastrointestinal adverse events compared to traditional iron salts, with an incidence rate ratio of 0.36 (95% CI 0.17-0.76, P < 0.01) in pregnant women. 2

Specific GI Side Effect Profile

• Ferrous bisglycinate 25 mg iron daily has the most favorable gastrointestinal side effect profile among equipotent iron formulations, with significantly fewer complaints than ferrous fumarate 40 mg or ferrous sulfate 50 mg. 6
• The frequency of black stools—a common cosmetic side effect that causes patient concern—is substantially lower with ferrous bisglycinate (8%) compared to ferrous fumarate (22%) or ferrous sulfate (31%). 6
• In cancer patients, only 17% experienced grade 1 gastrointestinal toxicity with ferrous bisglycinate versus 33% with ferrous sulfate. 5
• Low-dose ferrous bisglycinate supplementation (25 mg iron daily) is not associated with clinically significant gastrointestinal complaints requiring dose reduction, formula change, or discontinuation. 6

Clinical Positioning

According to the 2024 American Gastroenterological Association guidelines, ferrous bisglycinate is listed among the common oral iron preparations alongside ferrous sulfate, ferrous gluconate, ferrous fumarate, and polysaccharide-iron complex. 1 While the guidelines note that "no strong evidence suggests that any available oral formulation is more effective or better tolerated than others" in general populations, the specific research evidence demonstrates clear advantages for ferrous bisglycinate in terms of bioavailability and gastrointestinal tolerability. 2, 4, 6, 3, 5

Practical Considerations

• Ferrous bisglycinate may be preferred for iron prophylaxis, especially in women experiencing gastrointestinal side effects when taking other conventional iron formulas. 6
• The lower elemental iron content per tablet (25 mg versus 65 mg for ferrous sulfate or 106 mg for ferrous fumarate) requires clinicians to adjust their prescribing habits, but the enhanced bioavailability compensates for the lower dose. 1, 4
• The moderate cost ($2.40 for 30 pills) positions it between the least expensive option (ferrous sulfate) and more expensive alternatives, making it accessible for most patients. 1

Common Pitfalls to Avoid

• Do not assume ferrous bisglycinate requires the same elemental iron dosing as ferrous sulfate—25 mg of iron as bisglycinate is equivalent to 50 mg as sulfate due to superior bioavailability. 4
• Do not dismiss patient reports of better tolerance with ferrous bisglycinate as placebo effect—the reduced GI side effects are well-documented and clinically significant. 2, 6
• Do not overlook ferrous bisglycinate when patients report intolerance to traditional iron salts—switching to this formulation may improve adherence without requiring intravenous iron. 6, 5