Iron (Ferrous Bisglycinate)
Extremely strong evidence for treating confirmed iron-deficiency anemia, but iron should not be taken as a routine 'just in case' supplement without a blood test, since excess iron accumulates in the body and can be harmful, and iron overdose is a leading cause of pediatric poisoning deaths.
1. Overview
What it is
An essential mineral required for hemoglobin (oxygen transport in blood) and myoglobin (oxygen storage in muscle), and numerous enzymatic reactions.
How it works
Incorporated into hemoglobin within red blood cells to bind and transport oxygen from the lungs to tissues throughout the body.
Who should take it
People with lab-confirmed iron-deficiency anemia or low ferritin, menstruating women with heavy periods, pregnant women, and some vegans/vegetarians and endurance athletes.
Who should avoid it
People with hemochromatosis or other iron-overload conditions, and anyone without confirmed deficiency, since iron accumulates in the body over time.
Evidence summary
Extremely well-established evidence for correcting iron-deficiency anemia, one of the most common nutrient deficiencies worldwide (WHO); evidence does not support supplementation 'for energy' in people who are not actually deficient.
Scientific mechanism
Absorbed in the duodenum (heme iron more efficiently than non-heme), transported bound to transferrin, and incorporated into hemoglobin synthesis in developing red blood cells.
2. Scientific Evidence Rating
Very Strong Evidence — based on high-quality human evidence including systematic reviews, meta-analyses, randomized controlled trials, and major clinical guidance where available.
Ratings reflect the overall quality and consistency of human evidence, not marketing claims. Where evidence is mixed, this is stated explicitly rather than rounded up.
3. Safety Rating
4. Is It Worth Taking?
Extremely strong evidence for treating confirmed iron-deficiency anemia, but iron should not be taken as a routine 'just in case' supplement without a blood test, since excess iron accumulates in the body and can be harmful, and iron overdose is a leading cause of pediatric poisoning deaths.
5. Benefits
Each benefit is tagged with its own evidence strength — not every claim about a supplement is equally well supported.
- ★★★★★ Effectively treats and reverses iron-deficiency anemia
- ★★★★☆ Improves fatigue, exercise capacity, and cognitive symptoms specifically in people who are deficient
- ★★★★☆ Reduces adverse pregnancy outcomes associated with maternal iron-deficiency anemia
- ★☆☆☆☆ Provides no benefit — and carries real risk — when taken by people who are not iron deficient
6. Risks
Side effects
Constipation, nausea, dark stools, GI upset are common even at therapeutic doses.
Drug interactions
Reduces absorption of tetracycline/fluoroquinolone antibiotics and levothyroxine (thyroid medication) — separate dosing by several hours; antacids and PPIs reduce iron's own absorption.
Who should avoid it / use caution
7. Recommended Dosage
8. Best Time To Take
- On an empty stomach for best absorption, if tolerated
- With vitamin C-rich food to boost non-heme absorption; avoid taking with calcium, tea, or coffee, which reduce absorption
9. Food Sources
- Red meat, poultry, fish (heme iron, well absorbed)
- Beans, lentils, tofu, spinach (non-heme, less absorbed)
- Fortified cereals
10. Deficiency Symptoms
Supplementation is most clearly evidence-based when it corrects an actual shortfall like the ones below — not as a routine addition for people who are already sufficient.
- Fatigue and weakness
- Pale skin
- Shortness of breath
- Brittle nails
- Restless legs
- Pica (craving non-food items like ice)
FAQ
Should I take an iron supplement 'just in case' I'm low?
No — iron should be confirmed by a blood test (ferritin, hemoglobin) before supplementing, since unnecessary iron accumulates in the body and can cause harm over time.
Why does iron cause constipation?
Unabsorbed iron in the gut can slow motility; switching forms (e.g., bisglycinate, which is gentler) or taking with food can help, though it may modestly reduce absorption.
11. Scientific References
Ratings and content on this page are based on the consensus of the following types of high-quality sources. This is educational information, not individual medical advice.
Key Research Papers
- Review: oral iron therapy — efficacy and outcomes (PMC)
- Review: iron toxicity and pediatric poisoning risk (PMC)
General Reference Organizations
⚕️ This page does not diagnose, treat, cure, or prevent any disease. Iron (Ferrous Bisglycinate) is not a substitute for a varied diet or professional medical care. Always consult a qualified healthcare provider before starting any new supplement, especially if pregnant, breastfeeding, managing a health condition, or taking medication.