What are the signs of iron deficiency?

Iron deficiency anaemia causes weakness, fatigue, difficulty concentrating and impaired immune function and work performance.

Who is most likely to run low

People on vegetarian diets need 1.8 times as much iron as people who eat animal products.

What this means for you

Iron deficiency arrives slowly enough that most people explain it away. Tiredness that sleep does not fix, breathlessness on stairs that were fine last year, a foggy head at work, cold hands, hair that comes out more than it used to. Each of those has twenty other explanations, which is exactly why iron gets missed for months.

Two signs are more specific and worth knowing. A craving to chew ice, or to eat things that are not food, is a recognised feature of iron deficiency. And restless legs at night are more common in people who are low.

Established. Restless legs is the one of those that has been tested head to head. Giving iron cut severity scores by about four points on a forty-point scale, two to twelve weeks in. If your legs will not settle at night and nobody has ever looked at your iron, that is worth raising with your doctor.

Unsettled. Whether it helps the sleep itself is a different question, and the answer so far is no. Sleep quality did not improve in the same review, by questionnaire or by measurement, even while the leg symptoms eased. That null rests on three small trials and one measurement in eighteen people. It is too thin to settle anything, and it is the honest state of play.

Established. Iron deficiency anaemia causes weakness, fatigue, trouble concentrating and weaker immune function. In infancy it can cause cognitive and psychological effects, some of which might be irreversible, which is why it is taken so seriously in small children.

Low iron before anaemia shows up

You can be short of iron with a perfectly normal blood count, and that stage has been measured on its own. Tiredness is the symptom that reliably lifts when iron is given back. Measured stamina does not move at all, and neither did peak oxygen uptake across nine trials. Iron can make you feel less tired without making you fitter.

The mental side splits the same way. In non-anaemic children, teenagers and menstruating adults, iron improved anxiety, short-term memory, cognitive test scores and a general sense of physical wellbeing. Attention did not change. Depression did not change. Those last two are worth naming, because they are exactly what people hope a supplement will fix. All of this rests on what people reported about themselves in trials that were not always well blinded, so some of the lift may be expectation.

Unsettled. Giving that stage a drip does little either. Pooling eight trials of intravenous iron in people who were deficient without anaemia, haemoglobin rose by 3 g/L, which Cochrane calls clinically insignificant, and nothing measured reached the size the reviewers had set in advance as worth having. Quality of life and peak oxygen uptake came out very low quality. Treating a low ferritin in someone who feels well is not a settled thing to do.

Anaemic and short of iron are two separate findings

Myth. Being told you are anaemic means you are short of iron. Among 310 young children in Puno, Peru, iron deficiency accounted for 27.5 per cent of the anaemia. Inflammation accounted for 45.9 per cent, and other causes for the rest. Iron is the first thing to look for and it is the answer less than half the time, which is why the ferritin result matters more than the haemoglobin one.

Unsettled. The line itself moved in 2024. WHO reviewed its haemoglobin cutoffs and changed the one for children aged 6 to 23 months, while leaving the cutoff for the second trimester of pregnancy where it was. Recalculated on the same blood samples in that Peruvian group, the share of children that age counted as anaemic fell from 62 to 47 per cent. Nothing about the children changed. If a result is being read against a threshold, it is fair to ask which threshold.

Who should actually check

Women with heavy periods, people who are pregnant, people who have had gut surgery or live with coeliac or inflammatory bowel disease, and regular blood donors. Vegetarians and vegans belong on the list too, because they need roughly 1.8 times as much iron as people who eat meat, since plant iron absorbs less well.

Established. Donors are on that list for a measured reason. Across seven trials, oral iron cut the chance of being turned away for low haemoglobin at the next donation by about 60 per cent. If you give blood regularly and have never had your iron looked at, that is a conversation for the clinic rather than a reason to buy tablets.

Not for everyone. Do not start an iron supplement on a hunch. The symptoms above overlap with thyroid problems, B12 deficiency, sleep apnoea and depression, and in men and post-menopausal women unexplained iron deficiency can be the first sign of bleeding somewhere that needs finding. A ferritin test settles in one blood draw what a bottle of tablets only obscures.

Pregnancy is the setting where low iron has been studied hardest. Across 38 observational studies covering almost 32 million pregnancies, anaemia was linked to a 30 per cent higher chance of the baby growing poorly in the womb, and the trials of iron in pregnancy cut anaemia from 7.4 per cent to 4.0 per cent. What those trials did and did not show is a page of its own.

If you are confirmed low, the practical levers are real. Vitamin C with the meal improves absorption of plant iron, meat and fish improve it too, and tea, coffee and calcium taken at the same time work against it. And be wary of fixing a deficiency with spinach. It is the food the NIH names as looking rich in iron by content while delivering little, because the oxalate in it holds the iron back.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Where to get it from food

• Sesame seeds, whole, dried — 21 mg per 1 cup (116% DV)
• Oats, instant, fortified, plain, cooked fortified — 13.9 mg per 1 cup, cooked (77% DV)
• Sesame seed kernels, toasted — 9.96 mg per 1 cup (55% DV)
• Chicken, liver, all classes, cooked — 9.89 mg per 3 oz (55% DV)
• Corn flour, masa, white fortified — 9.69 mg per 1 cup (54% DV)

All iron sources ranked →

Full guide: Iron: why the number on the label is not the number your body gets