Full profile
| Also known as | Ferrous bisglycinate, Elemental iron |
|---|---|
| Best for | Cognition, energy, and mood support in iron-deficient individuals (often menstruating women) |
| Evidence grade | Grade B — Moderate — several human trials, some mixed results |
| Studied dose range | 18–65 mg elemental iron/day as bisglycinate, dependent on documented deficiency. Note the adult tolerable upper intake level is 45 mg/day elemental iron; the top of this range is defensible only under clinician-guided treatment of confirmed deficiency, not general use. |
| Time to effect | Correcting deficiency and any associated symptoms typically takes 4–12 weeks. |
| Best form | Iron bisglycinate — better tolerated and better absorbed than ferrous sulfate for most users. |
| Food sources | Red meat, Lentils and legumes, Fortified cereals, Dark leafy greens (non-heme) |
Evidence, honestly graded
Conditional B. The benefit is limited to iron-deficient individuals — do not blanket-dose iron-replete men or post-menopausal women, since excess iron carries a pro-oxidant and iron-overload risk rather than a cognitive benefit. This ingredient should be screened for (e.g. serum ferritin) before use, not included by default in a general-population formula.
See the full grading rubric — study type, replication, population match, and dose adequacy — in The Evidence Standard.
Side effects
- GI upset, constipation, or nausea, less common with bisglycinate than sulfate
- Dark stools (harmless)
Who should avoid it or check first
- Iron-replete individuals without documented deficiency — screen first
- Hemochromatosis or other iron-overload conditions
- Pregnant or breastfeeding without clinician-guided dosing
Interactions
- Reduces absorption of some antibiotics (tetracyclines, quinolones) and thyroid medication — separate the doses — discuss with a clinician
Stacks well with
- Vitamin C (enhances non-heme iron absorption)
Use caution stacking with
- Calcium or high-dose zinc at the same time (competes for absorption)
What to look for on a label
- Do not present as a general-population ingredient — state clearly that benefit is conditional on documented iron deficiency and that screening (e.g. serum ferritin) is recommended before use.
- State elemental iron delivered, not just the compound weight.
References
- Falkingham M, Abdelhamid A, Curtis P, Fairweather-Tait S, Dye L, Hooper L (2010). Nutrition Journal, 9:4Iron supplementation improved attention/concentration and IQ, concentrated in initially iron-deficient/anemic groups.
Grades and studied doses are our conservative reading of the human research, shown for education. They are not product claims, and a studied dose is not a recommended dose.
Revision history
Every change to this ingredient's evidence status, dated and explained. The full cross-library log lives at Evidence Updates.
- 2026-07-07New profile
Initial profile published at Grade B (conditional): the cognition benefit is specific to correcting iron deficiency or iron-deficiency anemia, not a general enhancer in replete adults.
See how Iron compares on grade, dose, and goal in the Evidence Explorer.
