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Iron
Iron is the one supplement where guessing can hurt you: the body has no exit for iron, so anything you don't need just piles up. So the first move isn't a pill, it's a blood test. Order a ferritin. If it's low, you're in for one of the most reliably felt fixes in nutrition: energy back, the afternoon slump gone, hair settling over months. If it's already full, the same pill builds silently toward overload and gives you nothing.
Do ยท Course Evidence Moderate Chapter Supplements

The tiredness people write off as their personality is often just low iron. In fatigued women with ferritin under fifty, four weeks of oral iron cut fatigue by twenty-nine percent against thirteen on placebo 1. The benefit was steepest under fifteen, shrank up to fifty, and vanished above it 2.

Ferritin is the protein that stores your iron, and the blood level tracks how much you have. Under thirty micrograms per litre is deficiency, even when your blood count looks normal 3. Empty stores with a normal count is the case most often missed.

When you're genuinely low, energy comes back first, focus next, hair over months. Attention and processing speed sharpen within weeks 4. Shedding slows as stores rebuild, new growth two to three months behind 5. Restless legs can respond even with normal bloodwork 6.

Take it right and you absorb more from fewer pills. A dose of sixty milligrams or more triggers hepcidin, which shuts the gut's iron door for a day 7. A second dose lands on a closed door. So every other day absorbs about a third more than daily, from the same pills 8.

Test before you treat. The ferritin number sets the decision.

On a long-term reflux pill like omeprazole, tell your prescriber: low stomach acid makes oral repletion slow and often incomplete, and an infusion may be needed 3.

For an adult who was low:

  • Weeks one to two: blood count rising; the most depleted feel it early.
  • Weeks four to eight: fatigue softens, stairs stop being an event 1.
  • Months two to four: focus sharpens, shedding drops, restless legs settle 6.
  • Months three to six: ferritin refills, nails stop splitting.

In someone genuinely deficient, this is among the most dependable nutritional fixes there is. In someone who wasn't, you feel nothing while your stores climb toward a problem you can't undo.

The fine print โ€” when to skip it, and what people get wrong

With a family history of haemochromatosis or unexplained high ferritin, get HFE genetic testing before any iron 3. Iron pills are a leading pediatric poisoning; lock the bottle.

New deficiency after sixty means a bowel workup before the pill 3. Stopping when the blood count looks fine leaves stores empty and symptoms return within a year 9.

References
  1. 1Verdon F, Burnand B, Stubi CL, Bonard C, Graff M, Michaud A, Bischoff T, de Vevey M, Studer JP, Herzig L, Chapuis C, Tissot J, Pecoud A, Favrat B (2003). Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ. link
  2. 2Krayenbuehl PA, Battegay E, Breymann C, Furrer J, Schulthess G (2011). Intravenous iron for the treatment of fatigue in nonanemic, premenopausal women with low serum ferritin concentration. Blood. link
  3. 3Snook J, Bhala N, Beales ILP, Cannings D, Kightley C, Logan RPH, Pritchard DM, Sidhu R, Surgenor S, Thomas W, Verma AM, Goddard AF (2021). British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut. link
  4. 4Pasricha SR, Tye-Din J, Muckenthaler MU, Swinkels DW (2021). Iron deficiency. The Lancet. link
  5. 5Trost LB, Bergfeld WF, Calogeras E (2006). The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. Journal of the American Academy of Dermatology. link
  6. 6Trenkwalder C, Winkelmann J, Oertel W, Virgin G, Roubert B, Mezzacasa A (2017). Ferric carboxymaltose in patients with restless legs syndrome and nonanemic iron deficiency: a randomized trial. Movement Disorders. link
  7. 7Moretti D, Goede JS, Zeder C, Jiskra M, Chatzinakou V, Tjalsma H, Melse-Boonstra A, Brittenham G, Swinkels DW, Zimmermann MB (2015). Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood. link
  8. 8Stoffel NU, Cercamondi CI, Brittenham G, Zeder C, Geurts-Moespot AJ, Swinkels DW, Moretti D, Zimmermann MB (2017). Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. The Lancet Haematology. link
  9. 9Camaschella C (2015). Iron-deficiency anemia. New England Journal of Medicine. link
Related in the handbook (12)
Helps
  • โ€” Low ferritin with normal hemoglobin is the classic case where iron helps โ€” energy back within weeks.
  • โ€” Restless legs is one of the clearest reasons to fix low iron โ€” replacing it is the first treatment to try.
  • โ€” Heavy periods from fibroids are a leading reason women run low. Fix the bleeding and the iron, not just one.
Works well with
  • โ€” Take iron with a vitamin-C source and you absorb noticeably more of it; a free upgrade.
Undermines
  • โ€” Tannins in coffee and tea block iron absorption, so keep your iron pill an hour clear of your morning cup.
Related
  • โ€” Take iron well away from thyroid medication, or it'll blunt the dose.
  • โ€” If periods are heavy, your iron is probably leaking out faster than food replaces it; ferritin and a supplement help.
  • โ€” Anyone with this iron-overload gene should avoid iron supplements โ€” they pour fuel on the fire.
  • โ€” If the grid points to iron deficiency, the fix is iron โ€” and one pill every other morning absorbs better than daily.
  • โ€” Liver is the densest, best-absorbed iron there is โ€” a weekly slice closes the gap a pill chases.
  • โ€” Phytic acid in grains and beans clamps onto iron so your gut can't absorb it โ€” soaking and souring free it.
  • โ€” An adjacent topic in the handbook.
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