The pattern most women recognise
The cluster is familiar once you know it: tiredness, breathlessness on the stairs, paler than usual, sometimes a sore tongue or a heart that flutters after a brisk walk. We've covered the full symptom catalogue in our tiredness piece, this page goes deeper on why it tends to land on women specifically.
One distinction worth making before the rest: low dietary iron is when you're consistently not eating enough iron-rich food to keep stores topped up. Iron deficiency anaemia (IDA) is a clinical condition, diagnosed by a blood test, where stores are depleted enough to affect how your blood carries oxygen. Low dietary intake is the more common starting point, and it doesn't always progress to IDA, but it's the place to start looking.
Why women specifically
Menstrual blood loss is the leading cause of iron deficiency in women aged 19 to 50. Every period removes iron, roughly 0.5mg per day averaged across the cycle, rising sharply during heavier flow, that your body then needs to replace from food. For most women on a varied diet, the balance holds. For those with heavier periods, the loss can outrun the replenishment month on month, drawing down stores before any obvious symptom appears.
The mechanism matters here. Iron is lost with red blood cells in menstrual fluid. Unlike some nutrients, your body can't manufacture iron; it can only recycle what's already in circulation and absorb more from food. A consistently heavy period creates a structural deficit that diet alone may not close, which is why the NHS says clearly: women with heavy periods should speak to a GP or a registered dietitian for more advice, not simply increase spinach intake and hope.
Pregnancy raises iron needs further still, because your body is building blood supply for two. The NHS recommends speaking to a midwife or GP about iron during pregnancy. The same principle applies: dietary adjustment helps, but the clinical picture needs a professional to read it.
What iron actually does
As the NHS puts it: iron is important in making red blood cells, which carry oxygen around the body. Your red blood cells contain a protein called haemoglobin. Haemoglobin binds to oxygen in the lungs and releases it to tissues everywhere else. Iron is what makes haemoglobin work.
When iron stores drop, your body makes fewer or smaller red blood cells, and each one carries less oxygen. The engine doesn't break, it just runs on less. Climbing stairs takes more effort because your muscles get less oxygen with each breath. Your heart beats harder to compensate. Your skin looks paler because there's less oxygenated blood near the surface. The whole cascade follows from one mineral running short.
The BDA also notes that iron supports muscle development during growth and is involved in enzyme activity and immune function. It's a quiet worker most of the time, which is why its absence announces itself through feel rather than a single obvious symptom.
The numbers
Women aged 19 to 49 need 14.8mg of iron a day. After 50, the figure drops to 8.7mg, the same as men. The difference exists entirely because of menstrual loss. American sites quote 18mg as the RDA for women; that's their figure, set by a different body against a different population. It's not ours.
Most people should be able to get the iron they need from their daily diet, as the NHS puts it. But "most people" conceals a gap: women with heavy periods, those who eat little or no meat, and those in pregnancy or early postpartum are all more likely to find the daily target harder to reach.
What to do this week
The most iron-dense foods are red meat and offal, where the iron is in haem form, absorbed more readily. Fish and poultry also contribute. Plant sources (pulses, dark leafy vegetables, fortified cereals, nuts and seeds) provide non-haem iron, which your body absorbs less efficiently but which still adds up meaningfully across a week.
Two pairing rules that make a meaningful difference. First: eat non-haem iron sources alongside a small amount of vitamin C. Vitamin C changes the form of non-haem iron in your gut, making it easier to absorb. A glass of orange juice with lentils, a squeeze of lemon over wilted spinach. Second: the BDA notes that tannins in tea and coffee make it harder for your body to absorb iron. Try to leave an hour between an iron-rich meal and your next cup.
When to see your GP
A few situations where dietary adjustment isn't the starting point and a GP appointment is.
If your periods are heavy and you're experiencing persistent tiredness, breathlessness, or heart palpitations, raise it at your next appointment. The GP will run a ferritin test, which measures your stored iron and gives a clearer picture than symptoms alone. As the NHS notes, iron tablets follow a blood test and a GP's recommendation, not a suspicion. High-dose iron supplementation without a diagnosis isn't a good idea; too much iron has its own side effects and can mask other causes.
If breathlessness or palpitations are new or pronounced, particularly if you're not someone who typically gets them, it's worth getting checked sooner rather than later. Both can have causes other than low iron, and a blood test rules things in or out quickly.
If you suspect low iron but your periods are normal and your diet is varied, keep a food log for a week and look at how often iron-rich foods appear. That's the kind of pattern we built the app to show, without requiring you to read a nutrition textbook to use it.
A short, honest note
This page is a guide, not a clinic. The symptom patterns described are drawn from NHS and BDA sources; they're useful for recognising when to ask questions, not for diagnosing yourself. If what you're reading keeps fitting after a couple of weeks of paying attention, see your GP. They'll run the right test and read the result in context, which is the bit a blog genuinely cannot do.