5 Signs You Might Be Low on Iron — and Why Fatigue Isn't the Useful One
THE SHORT ANSWER
Fatigue is the sign everyone looks for and the least useful one, because almost everything causes fatigue. The signs that actually point at iron are stranger: chewing ice, restless legs at night, cracks at the corners of your mouth, hair shedding, and nails that curve the wrong way. The other thing worth knowing is that a normal full blood count does not rule it out — you need ferritin, and it is not always included.*
01Why fatigue is the wrong thing to lead with
Every page about iron opens with tiredness, and tiredness is real — iron carries oxygen, so less iron means less oxygen delivered.
The problem is discrimination. Fatigue is caused by poor sleep, stress, thyroid disease, depression, viral illness, overtraining, low B12, and simply being a person in February. As a diagnostic signal it is close to noise.
The signs below are worth more precisely because they are odd. Nobody chews ice for no reason.
021. You are chewing ice
This has a clinical name — pagophagia — and it is a specific form of pica, the craving for things with no nutritional value. It is one of the more strongly associated signs of iron deficiency there is.
The mechanism is not fully settled. One proposal is that chewing ice produces a brief increase in blood flow to the brain, which would offer some temporary relief from the cognitive dullness of iron deficiency. What is better established is the pattern: the craving tends to fade within weeks once iron status is corrected.
If you are finishing drinks and then working through the ice, or buying bags of it, that is worth a blood test rather than a shrug.
032. Your legs will not settle at night
Restless legs syndrome — a crawling or aching urge to move the legs that eases with movement and is worst at rest — has one of the clearest links to iron on this list.
It is present in up to a quarter of people with iron deficiency anaemia.1 The mechanism runs through the brain rather than the blood: iron is required for dopamine production, and people with RLS show reduced central iron stores, with lower cerebrospinal fluid ferritin than controls and reduced stores visible on imaging.1
That last point has a practical consequence. The brain can be short of iron before blood measures look clearly abnormal, so neurological symptoms can arrive before anaemia does.
And there is trial evidence that correcting it helps. A randomised controlled trial in iron-deficient blood donors found significant improvements in RLS severity, fatigue and sleep quality after iron supplementation, with no difference between oral and intravenous routes.2
043. Cracks at the corners of your mouth
Angular cheilosis — fissures at the corners of the mouth that keep reopening — is a recognised clinical sign of iron deficiency, alongside a smooth tongue that has lost its usual texture.1
It is not exclusive to iron; B vitamin deficiencies and fungal infection do it too. But persistent cracking that will not heal, particularly with other signs here, belongs in the picture.
054. Hair shedding that is new or intense
Diffuse shedding rather than patchy loss. Low ferritin is repeatedly implicated, though the honest framing is that hair loss has a long list of causes — thyroid, postpartum changes, major stress, low protein intake — and iron is one item on it.
What makes it worth checking is the change. Not "I lose some hair" but "this is new, and there is noticeably more of it."
065. Nails that curve the wrong way
Koilonychia — spoon nails — is when the nail flattens and then dips in the middle, edges lifting, so it could hold a drop of water. It is one of the more visually distinctive signs.1
It is also a late one. Brittleness, splitting and ridging usually come first, and full spooning tends to appear in longer-standing deficiency. Worth knowing so you do not wait for it.
07The testing problem that catches most people
This is the most useful paragraph on the page.
A standard full blood count measures haemoglobin. Haemoglobin is what falls in anaemia. But iron stores can be substantially depleted while haemoglobin still reads normal — that is iron deficiency without anaemia, and it is a real state with real symptoms.
Ferritin is the marker for stores, and it is not always included by default. Ask for it by name. Transferrin saturation adds useful detail.
One caveat that cuts the other way: ferritin rises during inflammation and infection, so a result taken while you are unwell can look reassuring when it should not. Mention any recent illness.
We wrote the fuller version in the marker most people guess at.
08Do not supplement iron on a hunch
Iron is the one nutrient on this site where we would actively discourage speculative use.
It accumulates, and the body has no efficient route to excrete an excess. Supplementing without knowing your status is not the low-risk experiment it is with, say, magnesium.
If you have tested and you are low: Iron Complex pairs bisglycinate with vitamin C and the cofactors, and Iron Bisglycinate 25 mg is the standalone. Take it away from coffee, tea and calcium, which all interfere — the timing guide covers it.
And one expectation to set: iron reduces fatigue in low-ferritin women,3 but a 2025 meta-analysis found it does not reliably improve exercise performance in the same group.4 Feeling better and being faster are different outcomes.
09Who is most at risk
Menstruating women, particularly with heavy periods. Pregnancy. Endurance athletes. Blood donors. Vegetarians and vegans, since plant iron is absorbed less efficiently. Anyone with a condition affecting absorption, and anyone on long-term medication that reduces stomach acid.
10Frequently asked questions
Why do I crave ice?
Pagophagia is a form of pica strongly associated with iron deficiency. It commonly resolves within weeks of correcting iron status.
Can low iron cause restless legs?
It is one of the best-established triggers. RLS occurs in up to a quarter of people with iron deficiency anaemia, and iron is required for dopamine production.1
Can I be iron deficient with a normal blood test?
Yes. Haemoglobin can be normal while ferritin is depleted. Ask for ferritin specifically.
Does ferritin ever read falsely normal?
Yes — it rises with inflammation and infection, so testing while unwell can mislead.
Should I take iron just in case?
No. Iron accumulates and cannot be efficiently excreted. Test first.
How long until symptoms improve?
Trials measure at eight to twelve weeks.2 Ice cravings often go sooner; hair takes longest.
11References
- Clinical descriptions of iron deficiency signs — pallor, cheilosis, decreased tongue papillation, koilonychia, pagophagia and restless legs syndrome, including reduced central iron stores in RLS. Reference summary, ScienceDirect Topics: Pagophagia.
- The effect of parenteral or oral iron supplementation on fatigue, sleep, quality of life and restless legs syndrome in iron-deficient blood donors: a secondary analysis of the IronWoMan RCT. PMCID: PMC7284357.
- Verdon F, Burnand B, Fallab Stubi CL, et al. Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ. 2003;326(7399):1124. doi:10.1136/bmj.326.7399.1124
- Effect of iron supplementation on exercise performance of women with non-anemic iron deficiency or iron deficiency anaemia: a systematic review and meta-analysis. 2025.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article describes clinical signs for general information and is not a diagnostic tool. Persistent symptoms deserve a doctor.
