Iron

Your intake

What each level of iron does

Approximate dose-response bands. Individual response varies — these are starting points, not prescriptions.

1. Severely lowYOU ARE HERE

   0 mg – 5.94 mg

   Iron-deficiency anemia: fatigue, pale skin, brittle nails. More common in menstruating people.

2. Insufficient

   5.94 mg – 18 mg

   Below target — pair with vitamin C, avoid taking with coffee/tea/calcium.

3. Adequate

   18 mg – 27 mg

   DV (18 mg) met. Supports hemoglobin, oxygen transport, energy metabolism.

4. Therapeutic

   27 mg – 36 mg

   Used during iron repletion. Get ferritin tested before supplementing high doses long-term.

5. High

   36 mg – 45 mg

   Iron overload risk — especially for men and post-menopausal people.

6. Over upper limit

   45 mg – +

   Above UL (45 mg) — GI side effects and oxidative stress. Cut back unless under clinical care.

Overview

Central to oxygen transport (hemoglobin), oxygen storage (myoglobin), and electron transfer (cytochromes, iron-sulfur clusters). Tightly regulated because both deficiency (anemia, fatigue, cognitive impairment) and excess (Fenton oxidation, organ damage) carry real harm. Heme iron from animal foods is far better absorbed than non-heme iron from plants.

Functions

• ●Forms hemoglobin (4 heme groups per molecule, each binds one O2)
• ●Forms myoglobin (muscle oxygen reservoir)
• ●Cofactor in electron transport chain (cytochromes)
• ●Required for thyroid peroxidase, DNA synthesis, and immune function
• ●Substrate for neurotransmitter synthesis (dopamine, serotonin)

Mechanism

Heme iron is absorbed intact via heme carrier protein 1 (HCP1) at ~25% efficiency. Non-heme iron must be reduced from Fe3+ to Fe2+ by DCytb (reductase) and absorbed via DMT1 at ~5–10% efficiency, modulated by current iron status. Hepcidin (liver-secreted) is the master regulator: high stores → high hepcidin → reduced absorption and reduced macrophage iron release.

Benefits

• ●Corrects iron-deficiency anemia (fatigue, exercise intolerance, cognitive impairment)
• ●Improves restless leg syndrome when ferritin is low
• ●Supports normal cognitive development in children
• ●Treatment for menorrhagia-associated iron loss

Deficiency

Most common nutritional deficiency worldwide. Affects ~10% of premenopausal women in the developed world; higher in low-income countries. Diagnosed via ferritin (<30 ng/mL flags iron-deficient erythropoiesis even with normal hemoglobin).

Excess

Hereditary hemochromatosis (HFE gene) drives iron overload in ~1/200 Northern Europeans. Excess catalyses Fenton chemistry — generating hydroxyl radicals that damage liver, heart, pancreas, joints. Never supplement iron without documented deficiency.

Forms

• Ferrous bisglycinate (chelated)
  Best-tolerated; well-absorbed at lower elemental doses
• Ferrous sulfate
  Cheap, clinically validated; GI side effects common
• Ferrous fumarate / gluconate
  Standard alternatives; similar efficacy, varying tolerance
• Heme iron polypeptide
  Bovine-derived; better absorption, less GI impact, higher cost
• Iron carbonyl
  Slow-release; lower GI distress
• IV iron (sucrose, dextran, ferumoxytol)
  For severe deficiency or oral intolerance

Food sources

• Beef (cooked) · 3 oz2.5 mg heme
• Chicken liver (cooked) · 3 oz11 mg heme
• Lentils (cooked) · 1 cup6.5 mg non-heme
• Spinach (cooked) · 1 cup6.5 mg non-heme
• Tofu · 1/2 cup3 mg non-heme
• Pumpkin seeds · 1 oz2 mg non-heme

Supplement forms

Ferrous bisglycinate is the best-tolerated chelated form and well-absorbed at lower elemental doses. Ferrous sulfate is the cheapest and clinically validated but causes constipation and GI distress in many users. Take on an empty stomach with vitamin C; avoid taking with calcium, coffee, or tea. Alternate-day dosing achieves similar repletion with better tolerability.

Bioavailability

Heme iron ~15–35% absorbed regardless of co-ingested foods. Non-heme iron 2–20%, strongly modulated by vitamin C (boosts 3–4×), phytate, polyphenols (tea, coffee), calcium (all inhibit). High-dose iron supplementation transiently elevates hepcidin for ~24 hours — alternate-day dosing increases fractional absorption.

Longevity relevance

Adequacy (not excess) is the longevity-relevant range. Higher serum ferritin in non-deficient adults correlates with insulin resistance, hepatic fat, and modest mortality increase — particularly in post-menopausal women and men who no longer lose iron monthly. Routine multivitamins for men should not contain iron unless documented need.

Relationships

References

• NIH ODS — Ironguideline
• Linus Pauling Institute — Ironreview
• Stoffel — alternate-day iron dosing (Lancet Haematol 2017)study

About Iron

Hemoglobin, myoglobin, oxidative phosphorylation.

Role

Oxygen transport

Daily target

18 mg (DV)

Upper limit

45 mg

Also called

iron, ferrous, ferrous sulfate, ferrous fumarate, ferrous bisglycinate, ferric

Forms with lower absorption: ferric oxide, elemental iron. Prefer better-absorbed forms when supplementing.