Iron

Also known as: iron bisglycinate, ferrous sulfate, ferrous bisglycinate chelate

Grade A — Strong Evidencemineralfoundational
18–45 mgEmpty stomach with vitamin C for best absorption. Every other day may improve absorption.

Essential for oxygen transport and energy. ONLY supplement if deficient — excess iron is a pro-oxidant. Bisglycinate form preferred.

⚡Energy
Last reviewed: 2026-03-11

Evidence

Grade A

Studies

3

Interactions

5

Forms

4

Evidence Rating: Grade A — Strong Evidence

Multiple high-quality RCTs, systematic reviews, or meta-analyses with consistent findings.

Forms Comparison

Iron Bisglycinate

✓ High Absorption

Chelated form that is much gentler on the stomach with high absorption. Preferred form.

sensitive stomachspregnancygeneral deficiency

Ferrous Sulfate

~ Moderate Absorption

Most prescribed form. Effective but commonly causes GI side effects (constipation, nausea).

clinical deficiencybudget

Ferrous Fumarate

~ Moderate Absorption

Higher elemental iron content. Similar GI side effects to ferrous sulfate.

severe deficiency

Iron Polysaccharide Complex

~ Moderate Absorption

Slow-release form with fewer GI effects than sulfate, but possibly lower peak absorption.

GI-sensitive individuals

Interaction Warnings

CalciumModerate

Calcium inhibits iron absorption. Separate by 2+ hours.

Thyroid medicationsModerate

Iron reduces levothyroxine absorption. Separate by 4 hours.

Coffee/tea (tannins)Moderate

Block absorption — separate by 1 hour

ZincLow

May compete for absorption at high doses

Vitamin CLow

Doubles absorption — take together for deficiency

⚠️ Important Notes

  • Only supplement if deficient — excess iron is harmful
  • Get ferritin levels tested first
  • Bisglycinate form is gentler on stomach
  • Keep away from children — overdose risk

Clinical Evidence (3 studies)

Iron deficiency without anemia — common, overlooked, treatable

Soppi ET. (2018) — Clin Case Rep

Non-anemic iron deficiency causes fatigue, impaired cognition, and reduced exercise capacity

View on PubMed

Ferrous bisglycinate significantly better tolerated

Tolkien Z et al. (2015) — PLoS ONE

Bisglycinate has fewer GI side effects than ferrous sulfate

View on PubMed

Alternate-day iron dosing improves absorption

Moretti D et al. (2015) — Blood Adv

Alternate-day dosing improves absorption vs daily

View on PubMed

Alternatives to Consider

These supplements target similar goals and may be worth considering alongside or instead of Iron.

Potassium

Grade A

Critical electrolyte for heart and muscle function. Most people need more, but get it from food — supplemental doses are limited.

⚡ Energy

Vitamin B6

Grade A

Essential coenzyme for neurotransmitter synthesis (serotonin, GABA, dopamine). Strong evidence for PMS. Deficiency common in those on OCP or with poor diet.

⚡ Energy

Iodine

Grade A

Essential trace mineral for thyroid hormone synthesis. Critical for metabolic rate and cognitive development. Most people get enough from iodized salt — test before supplementing.

⚡ Energy

Related Supplements

Iodine

Grade A — Strong Evidence

Essential trace mineral for thyroid hormone synthesis. Critical for metabolic rate and cognitive development. Most people get enough from iodized salt — test before supplementing.

B-Complex

Grade B — Moderate Evidence

Group of essential vitamins for energy metabolism, nervous system function, and mood. Methylated forms preferred for MTHFR variants.

Potassium

Grade A — Strong Evidence

Critical electrolyte for heart and muscle function. Most people need more, but get it from food — supplemental doses are limited.

Vitamin B6

Grade A — Strong Evidence

Essential coenzyme for neurotransmitter synthesis (serotonin, GABA, dopamine). Strong evidence for PMS. Deficiency common in those on OCP or with poor diet.

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⚕️ Important Disclaimer

This information is for educational purposes only. It is not medical advice. Always consult a healthcare provider before starting any supplement regimen, especially if you take medications or have health conditions.

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