A patient describes a racing heart, breathlessness on the stairs, difficulty concentrating, poor sleep, fatigue that rest does not fix, and a general sense of being on edge. Every one of those is on the anxiety symptom list. Every one of them is also on the iron deficiency list.
This is the most common correctable finding I turn up in anxious patients, and the reason it gets missed is specific: iron deficiency is routinely screened for with haemoglobin, and you can be substantially iron deficient with a perfectly normal haemoglobin.
Deficiency comes before anaemia
Iron depletion happens in stages. Stored iron falls first — that is what ferritin measures. Then iron available for making red blood cells falls. Only at the end does haemoglobin drop enough to be called anaemia.
The middle stage, iron deficiency without anaemia, is where a lot of symptomatic people sit. A complete blood count comes back normal, everyone concludes iron is fine, and nobody measures ferritin. Meanwhile the patient has the fatigue, cognitive fog, exercise intolerance and irritability that low iron produces.
Why iron affects mood and anxiety
Iron is a cofactor for tyrosine hydroxylase and tryptophan hydroxylase — the rate-limiting enzymes in dopamine, noradrenaline and serotonin synthesis. It is also required for oxygen transport, for mitochondrial energy production, and for myelination.
The clearest clinical evidence of iron's neurological role is restless legs syndrome, which is strongly associated with low brain iron and treated with iron repletion, with a widely used treatment threshold of ferritin below about 75 ng/mL. Restless legs fragments sleep, and fragmented sleep raises anxiety — so iron can reach anxiety by more than one route.
In children and adolescents, iron deficiency is associated with more severe ADHD symptoms and with cognitive and behavioural effects that improve with repletion in some studies.
Who is at risk
- Menstruating women, particularly with heavy periods — by far the largest group. Fibroids, adenomyosis and copper IUDs increase losses.
- Pregnancy and the postpartum period, where requirements rise sharply and postpartum depletion is common after blood loss at delivery.
- Vegetarians and vegans: non-haem iron is less bioavailable and phytates inhibit absorption.
- Endurance athletes, through gastrointestinal losses, haemolysis and hepcidin effects.
- Gastrointestinal causes: coeliac disease, inflammatory bowel disease, long-term PPI use, H. pylori, bariatric surgery.
- Anyone with unexplained iron deficiency and no obvious source of loss — particularly men and post-menopausal women, where gastrointestinal bleeding must be excluded. This is not a nutritional workup; it is a medical one.
Other pointers: hair shedding, brittle nails, cold intolerance, headaches, pica (craving ice is classic), and shortness of breath on exertion that is out of proportion to fitness.
What to test, and how to read it
Ask for ferritin, plus a complete blood count, plus CRP. Transferrin saturation helps when the picture is unclear.
Two interpretation traps:
- Ferritin rises with inflammation. It is an acute-phase reactant, so infection, autoimmune disease and obesity can lift it into the normal range while stores are genuinely low. That is why CRP belongs on the same draw — a "normal" ferritin with a raised CRP does not rule out deficiency.
- The lab's lower limit is not a clinical threshold. Many labs flag ferritin as low only below 10–15 ng/mL. Symptomatic iron deficiency is widely recognised below 30 ng/mL, and for restless legs the treatment threshold used is around 75. A result of 18 ng/mL reported as "normal" in a fatigued, anxious patient with heavy periods deserves attention rather than dismissal.
Repletion, and the parts people get wrong
Correction is straightforward but slower than most people expect, and dosing has moved:
- Alternate-day dosing absorbs better than daily. A single dose raises hepcidin, which blunts absorption for the next 24 hours, so 100–200 mg of elemental iron every other day is now often preferred to the same amount daily — with fewer gastrointestinal side effects.
- Take it with vitamin C or a citrus source, and away from tea, coffee, calcium and antacids, all of which inhibit absorption.
- Expect three to six months. Symptoms often improve before ferritin looks respectable, and stores take longer to rebuild than the blood count does.
- Recheck rather than assume. Ferritin and CBC at three months tells you whether the plan is working and whether losses are ongoing.
- Intravenous iron is appropriate for malabsorption, intolerance of oral iron, or when repletion needs to be fast — a decision for your physician.
Do not self-supplement iron indefinitely without testing. Iron overload is a real condition, hereditary haemochromatosis is not rare, and unnecessary iron is not harmless.
Where this sits in an anxiety workup
To be clear about what this is not: iron deficiency is not a common cause of anxiety disorders, and correcting it does not treat one. Most anxious patients I see have normal iron and need anxiety treatment — therapy, sometimes medication — rather than a supplement.
But when a patient has both anxiety and a plausible reason to be iron deficient, checking ferritin costs very little and occasionally changes everything. It also stops the reverse error, which is treating breathlessness and palpitations as panic when they are physiological.
This is standard in our functional psychiatry assessments: ferritin with CRP, alongside thyroid function, B12, folate and vitamin D where the history warrants it. Where a deficiency turns up, we correct it and coordinate with your primary care physician on finding the cause — because in iron deficiency, the cause matters as much as the number. Dietary strategy for keeping levels up afterwards is part of a nutrition consultation.
FAQs
Can iron deficiency cause anxiety symptoms?
It can produce symptoms that closely overlap with anxiety — palpitations, breathlessness, fatigue, poor concentration, irritability and disturbed sleep — and it can worsen an existing anxiety disorder, partly by fragmenting sleep through restless legs. It is not a common cause of anxiety disorders, but it is a correctable contributor worth ruling out.
What ferritin level is considered low?
Many labs only flag ferritin below 10–15 ng/mL, but symptomatic iron deficiency is widely recognised below 30 ng/mL, and for restless legs syndrome a treatment threshold around 75 ng/mL is used. Ferritin should be interpreted alongside CRP, since inflammation raises it independently of stores.
Can I be iron deficient with normal haemoglobin?
Yes, and it is common. Stored iron falls before haemoglobin does, so a normal complete blood count does not rule out deficiency. That is why ferritin needs to be measured specifically rather than inferred from the CBC.
How long does it take to feel better after starting iron?
Often a few weeks for energy and concentration, but three to six months to rebuild stores. Alternate-day dosing with vitamin C, away from tea, coffee and calcium, absorbs better than daily dosing and causes fewer gastrointestinal side effects. Retest at around three months.
Should I just take an iron supplement to be safe?
No. Test first. Iron overload is a real risk, hereditary haemochromatosis is not rare, and unexplained iron deficiency in men or post-menopausal women needs a medical workup to exclude gastrointestinal bleeding rather than being covered up with a supplement.
