Benefits
Fewer Stomach and Bowel Side Effects
In a 2023 meta-analysis, pregnant women taking ferrous bisglycinate reported about 64% fewer gastrointestinal adverse events than those on other iron forms (incidence rate ratio 0.36). In a Danish trial of 80 pregnant women, 25 mg iron as bisglycinate caused fewer GI complaints than 50 mg as ferrous sulfate. In most of these comparisons the bisglycinate group took less elemental iron, so part of the advantage may come from the lower dose.
Absorption Compared With Iron Salts
In a 2000 radio-iron study in 10 iron-sufficient men eating iron-fortified maize porridge, iron from bisglycinate was absorbed about four times as well as iron from ferrous sulfate (6.0% vs 1.7%); in fortified bread it was absorbed about twice as well. In a Danish pregnancy trial, 25 mg iron as bisglycinate matched 50 mg as ferrous sulfate for preventing iron deficiency, but in a 480-woman Cambodian trial, 18 mg as bisglycinate raised ferritin less than 60 mg as ferrous sulfate. A 2023 meta-analysis found a modest hemoglobin advantage in pregnant women and none in children.
Partial Resistance to Phytates (Not to Tea or Espresso)
In absorption studies in 74 people eating fortified breakfasts, the bisglycinate chelate partly resisted the blocking effect of phytates (found in cereals and grains), but tea and espresso-type coffee still cut its absorption by about 50%; weaker American-type coffee had no significant effect. Oxalates (in spinach) have not been tested. As with any iron, take it apart from tea and coffee.
Pregnancy Iron Supplementation
Pregnancy raises the iron RDA from 18 to 27 mg/day. Over half of the bisglycinate trials were done in pregnant women: in a Danish trial, 25 mg iron/day as bisglycinate was not inferior to 50 mg as ferrous sulfate for preventing iron deficiency and anemia, with fewer stomach complaints. This matters when morning sickness already makes iron hard to take. Iron in pregnancy should be taken as advised by a midwife or doctor.
Option for People Who Cannot Tolerate Iron Salts
People who stop iron salts because of nausea, cramps or constipation may manage bisglycinate better, as the pregnancy trials suggest. There are no trials of bisglycinate in inflammatory bowel disease; in a small 2006 absorption study in 10 people with Crohn's disease, iron from bisglycinate was absorbed less well than iron from ferrous calcium citrate. People with bowel disease who need iron should have the form and route chosen by their doctor.
Mechanism of action
Glycine Chelate Stability
Iron ion bonded to two glycine molecules in stable chelate. Stays soluble even at pH 6, which may explain its partial resistance to phytates; tea and espresso-type coffee still inhibit it. Absorbed via standard iron transport (DMT1) and potentially via dipeptide transporters as an intact glycine complex.
Less Free Iron in the Gut (Unproven Hypothesis)
Free Fe²⁺ in GI tract may generate reactive oxygen species that irritate the gut lining, and a chelate is thought to release less of it. This has not been shown directly: in a 480-woman Cambodian trial, a marker of gut inflammation (fecal calprotectin) did not differ between bisglycinate, ferrous sulfate and placebo.
Absorption Inhibitors and Iron Status
Phytates and polyphenols bind free iron and reduce absorption. The chelate partly resists phytates, but tea and espresso-type coffee still halved its absorption in human testing, so the protection is incomplete. Absorption from bisglycinate is regulated by the body's iron status like other non-heme iron, falling as iron stores fill.
Standard Iron Functions
Once absorbed, iron functions identically regardless of supplemental form — incorporated into hemoglobin (oxygen transport), myoglobin (muscle oxygen storage), cytochromes (electron transport), iron-sulfur cluster enzymes. In women with low iron stores, iron supplements reduced fatigue in a trial that used ferrous sulfate (reducing tiredness and fatigue is also an authorized EU claim for iron); no bisglycinate trial has measured fatigue. Iron is needed for normal immune function, but supplements have not been shown to reduce infections: a review of 28 trials in children found no change in overall infections and slightly more diarrhea.
Clinical trials
Systematic review and meta-analysis, Fischer et al., Nutrition Reviews 2023 (University of British Columbia): trials of at least 4 weeks comparing ferrous bisglycinate with other iron supplements, searched to July 2020.
9 trials in pregnant women and 4 in children pooled; 4 further trials in men and non-pregnant women reviewed without pooling.
In pregnant women, bisglycinate gave higher hemoglobin than other iron forms (standardized mean difference 0.54) and fewer gastrointestinal adverse events (incidence rate ratio 0.36); the ferritin difference was not significant. In children there was no difference in hemoglobin or ferritin. In 8 of the 9 pregnancy trials the bisglycinate group took less elemental iron than the comparison group. The authors concluded bisglycinate shows some benefit in pregnancy and that more trials are needed in other groups.
Randomized, double-blind trial in Denmark (Milman et al., 2014), from weeks 15-19 of pregnancy to delivery. The bisglycinate product was Aminojern, whose maker, Pharmovital ApS, co-funded the study.
80 healthy pregnant Danish women, 40 per group.
Iron deficiency and anemia were uncommon in both groups and not significantly different, so 25 mg iron as bisglycinate was not inferior to 50 mg as ferrous sulfate for prevention. GI complaints were less frequent with bisglycinate (P=0.001). Because the doses differed, the trial cannot separate the effect of the form from the effect of the lower dose.