Will iron stop me getting altitude sickness?

No. The best available randomised evidence shows haemoglobin mass increases without a meaningful reduction in acute mountain sickness.

How far in advance should I start?

Eight to twelve weeks. Ferritin moves slowly on oral iron.

Daily or alternate-day dosing?

Alternate-day. It absorbs better because hepcidin stays elevated for about a day after a dose.

What ferritin level should I aim for?

Above 30-50 mcg/L is the usual threshold for benefit. Above that, extra iron adds risk rather than performance.

Can I just eat more red meat?

Diet maintains stores well but corrects an existing deficit very slowly. Supplementation is the practical route for repletion.

Outcome

Moderate Evidence

Effectiveness 3/5

Iron for Altitude Adaptation

Iron is one of the few supplements with a genuine physiological rationale at altitude, but only for people who start iron-deplete.

Overview

Iron is one of the few supplements with a genuine physiological rationale at altitude. Acclimatisation depends on hypoxia-driven erythropoiesis, and building new haemoglobin consumes iron quickly. If stores are low before you ascend, the red cell mass expansion that underpins adaptation is capped by substrate, not by drive. The corollary is that this is a repletion story, not an enhancement story. People who arrive at altitude with comfortable ferritin gain little from more iron, and loading a replete person carries real downside.

In iron-deficient trekkers, athletes and menstruating women, repletion started 8-12 weeks before ascent improves the haemoglobin response to hypoxia and exercise tolerance at altitude. What iron does not do is prevent acute mountain sickness. A 2025 randomised trial of intravenous iron found increased haemoglobin mass without a meaningful reduction in mountain sickness scores. Gradual ascent, and acetazolamide where appropriate, remain the tools for that problem.

Best suited to

Ferritin below 30-50 mcg/L before a trip

Endurance athletes training at altitude

Menstruating women planning a trek

Frequent blood donors

Vegetarian and vegan travellers

Anyone with a documented low haemoglobin response to hypoxia

How It Works

Low oxygen stabilises hypoxia-inducible factor, which drives erythropoietin release and a sustained increase in red cell production. Each new red cell needs iron for its haemoglobin, so the marrow draws heavily on ferritin stores during the first weeks at altitude. When stores are inadequate, erythropoietic drive is present but unmet, and the haemoglobin rise is blunted. Iron status also modulates the pulmonary vascular response to hypoxia, which is why iron has been studied in hypoxic pulmonary hypertension as well as in mountaineers.

A single iron dose raises hepcidin for roughly 24 hours, which suppresses absorption of the next dose. Alternate-day single doses therefore deliver more absorbed iron than the same total split across each day, and they cause fewer gastrointestinal complaints. Vitamin C and an empty stomach improve uptake; tea, coffee, calcium and dairy reduce it substantially.

Mechanistic steps

HIF stabilisation under hypoxia

Erythropoietin release

Marrow iron demand rises

Haemoglobin mass expansion

Hepcidin-limited absorption

Pulmonary vascular modulation

Dosing & Protocol

Scenario	Dose	Form	Timing
Ferritin below 30 mcg/L	40-65 mg elemental iron, alternate days	Ferrous sulfate, fumarate or gluconate	Empty stomach with vitamin C
Ferritin 30-50 mcg/L	40 mg elemental iron, alternate days	Any ferrous salt	Empty stomach
Ferritin above 50 mcg/L	No supplementation indicated	-	-
GI intolerance	Lower elemental dose or ferrous gluconate	Gluconate or bisglycinate	With a small snack

1
Test ferritin first· 12 weeks out
Iron supplementation without a baseline measurement is guesswork with a real downside. Ask for ferritin and a full blood count.
2
Start alternate-day dosing· Weeks 1-8
40-65 mg elemental iron every other morning on an empty stomach with a source of vitamin C.
3
Protect absorption· Ongoing
Keep tea, coffee, dairy and calcium supplements at least two hours away from the dose.
4
Recheck before departure· 2 weeks out
Repeat ferritin and haemoglobin. Rising values confirm the protocol is working.
5
Continue at altitude, then stop· During and after
Carry on during exposure, then recheck afterwards and discontinue once replete.

Repletion is slow. Ferritin typically takes 8-12 weeks to move meaningfully, which is why last-minute supplementation before a trek accomplishes little. If your departure is three weeks away and ferritin is very low, that is a conversation with a clinician about intravenous iron rather than a reason to double the oral dose.

More is not faster

Splitting iron into two or three daily doses raises hepcidin and reduces total absorption while increasing nausea and constipation. One dose every other day is the better-absorbed schedule.

Evidence

The strongest evidence is physiological rather than outcome-based: iron status predicts the erythropoietic response to hypoxia, and correcting deficiency restores it. Trials in trekkers and in hypoxic pulmonary hypertension support the link between iron availability and the body's handling of low oxygen. A 2025 randomised trial in the Journal of Applied Physiology gave intravenous iron or erythropoietin before altitude exposure. Haemoglobin mass rose, but acute mountain sickness scores did not meaningfully improve. Read that as a clean separation of two questions: iron helps you build oxygen-carrying capacity, and it does not treat altitude illness.

Best available evidence: Randomised trials of iron loading plus physiological studies of the hypoxic response
Typical effect: Improved haemoglobin response and exercise tolerance in iron-deficient individuals
No effect on: Acute mountain sickness incidence or severity
Studied approach: Repletion guided by ferritin, started weeks before ascent
Certainty of evidence: Moderate

Studies linked to this pairing.

Impact of intravenous iron or exogenous erythropoietin on hemoglobin mass, exercise performance, and acute mountain sickness during altitude exposure

Score: 6/10

2025

rct

Intravenous iron increased hemoglobin mass but did not meaningfully reduce acute mountain sickness scores at altitude.

View source

Safety

Gastrointestinal side effects are the common problem: nausea, constipation, dark stools and epigastric discomfort. Alternate-day dosing and a lower elemental dose usually resolve them. The serious concern is supplementing without testing. Iron overload is cumulative and damaging, and haemochromatosis is common enough that unguided loading is a genuine risk. Iron tablets are also a leading cause of poisoning in young children, so storage matters.

Do not supplement blind

Check ferritin before starting and recheck afterwards. If you have haemochromatosis, chronic liver disease or a history of transfusions, iron supplementation should be clinician-directed only.

Interactions & Conflicts

Interacts with	Severity	Mechanism	Action
Levothyroxine	high	Iron binds thyroxine in the gut and reduces absorption	Separate by at least four hours
Tetracycline and quinolone antibiotics	high	Chelation reduces absorption of both drug and iron	Separate by at least four hours
Proton pump inhibitors	moderate	Reduced gastric acid impairs iron absorption	Take with vitamin C; expect slower repletion
Calcium supplements, tea and coffee	moderate	Competitive inhibition and polyphenol binding	Keep two hours clear of the dose

Iron does not replace altitude planning. No supplement substitutes for a graded ascent profile, adequate hydration and descent when symptoms escalate. If you are considering acetazolamide or dexamethasone for a fast ascent, that decision sits with a travel medicine clinician and is independent of iron status.

References

Impact of intravenous iron or exogenous erythropoietin on hemoglobin mass, exercise performance, and acute mountain sickness during altitude exposure. J Appl Physiol. 2025
WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. World Health Organization, 2020
Wilderness Medical Society clinical practice guidelines for the prevention and treatment of acute altitude illness

Frequently Asked Questions

Medical Disclaimer

The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.

Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.