You've been tired for weeks. Not the normal kind — the kind a full night's sleep doesn't touch, where the stairs feel steeper than they used to, where a session at the gym leaves you flattened for the rest of the day. Before you reach for another supplement, it's worth asking a more specific question: is this iron?

Iron deficiency is one of the most common nutritional gaps in the UK, and women carry most of that burden — not through any fault of their own, but because of what their bodies do every month. Here's what the evidence actually shows about the signs, who's genuinely at risk, and when supplementing helps versus when it's papering over something only a blood test would catch.

The signs worth mentioning to your GP

Iron deficiency builds slowly, which is exactly why it's easy to write off as "just being busy" or "getting older." The NHS lists a fairly specific set of symptoms, and a handful come up often enough to be worth naming directly.^[1]

• Fatigue that doesn't lift with rest — the most common complaint, and the easiest one to dismiss.
• Paler skin, breathlessness or heart palpitations — signs your blood is carrying less oxygen than it should.
• Hair shedding more than usual, or spoon-shaped nails — visible changes that often get blamed on stress first.
• Restless legs, or an odd craving for non-food items like ice — less common, but specific enough to flag to a GP by name.

Why this lands on women specifically

The UK Reference Nutrient Intake for iron is 14.8mg a day for menstruating women aged 19 to 49, against 8.7mg for men and postmenopausal women — the widest sex-based gap in any standard nutrient table, and it exists for one plain reason: monthly blood loss.^[2] We've written before about how few nutrients actually justify a separate "women's" formula — iron is the one that genuinely does.

Heavy periods, known clinically as menorrhagia, are — alongside pregnancy — the leading cause of iron deficiency anaemia in women of reproductive age, according to the NHS.^[1] The numbers bear that out. A recent analysis of the National Diet and Nutrition Survey found that around one in five UK women of reproductive age are iron deficient, with more than a quarter falling short of the lower reference nutrient intake in their diet altogether.^[3]

What a blood test actually tells you

Here's the part that's easy to skip: you can't diagnose iron deficiency from symptoms alone, and guessing wrong in either direction has consequences. A GP will usually run a full blood count — no special preparation needed — to check your red blood cell levels before recommending anything.^[1] If the cause isn't obvious, they may look further, including checking for blood loss elsewhere in the body.

This matters because treatment for a confirmed deficiency looks different from general maintenance. NHS-prescribed iron tablets for anaemia are typically taken for around six months and dosed considerably higher than what you'd find in a daily supplement — because they're correcting a measured shortfall, not topping up a borderline diet.^[1]

Topping up a gap versus treating a diagnosis

If your blood test comes back normal but you know your diet runs light on iron — little red meat, not many pulses, or a heavy training schedule that increases iron turnover — a lower-dose daily supplement is a reasonable way to close that gap. That's a genuinely different job to correcting a diagnosed deficiency, and the label should reflect it.

This is where a capsule dosed close to the reference intake does more good than a mega-dose you don't need. Our Vegan Iron Complex delivers 14mg of iron as ferrous fumarate, alongside 400mcg of folic acid and 100mcg of vitamin B12 — sitting close to the 14.8mg figure above rather than overshooting it.

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Iron contributes to the normal formation of red blood cells and haemoglobin, to normal oxygen transport around the body, and to the reduction of tiredness and fatigue — all EFSA-authorised claims, and all reasons the mineral matters day to day, not just when a blood test flags a problem.^[4]

One caution worth taking seriously: iron isn't a supplement to take "just in case." Unlike most vitamins, the body has no efficient way to get rid of excess iron, so taking more than you need — especially over years — can let it build up to damaging levels. The NHS describes this build-up, known as iron overload, most commonly in the context of haemochromatosis, a genetic condition affecting the liver, joints and heart — but the underlying mechanism is the same reason unnecessary, indefinite iron supplementation isn't something to do casually.^[5] This is one supplement where more is not automatically better, and it isn't something men or postmenopausal women should take routinely without a specific reason.

The gold standard here is a blood test first

Becoming the standard, in this case, isn't about finding the strongest supplement on the shelf. It's about matching the dose to the actual gap, and knowing when "I'm always tired" deserves a blood test rather than a guess. If your diet's the issue, a sensible daily amount is worth keeping in the cupboard. If your body's telling you something more specific is going on, that's a conversation for your GP — not the supplement aisle.

Frequently asked questions

How long does it take for an iron supplement to work?

For a confirmed deficiency, NHS guidance is to expect around six months of treatment before iron stores fully recover, even though tiredness and other symptoms often start easing within a few weeks.^[1] For a general dietary top-up rather than a diagnosed shortfall, there's no fixed timeline — it depends on how large the gap was to begin with.

Can you take iron supplements every day, long-term?

Only if there's a genuine reason to. A low-dose daily supplement to cover a dietary gap is generally considered low-risk for someone who needs it, but iron shouldn't be taken indefinitely "just in case" — excess iron builds up in the body rather than being excreted, and unnecessary long-term use has been linked to iron overload.^[5] If you're not sure whether you need it, a blood test settles the question.

What's the difference between iron deficiency and iron deficiency anaemia?

Iron deficiency means your iron stores are running low. Anaemia is what happens once that shortfall is severe enough to reduce your red blood cell count and affect how well oxygen moves around your body. You can be iron deficient without yet being anaemic, which is part of why a blood test — not symptoms alone — is how a GP tells the two apart.

Do vegetarians and vegans need more iron?

Not necessarily more, but the iron in plant foods (non-haem iron) is absorbed less efficiently than the iron in meat (haem iron), so vegetarians and vegans often need to pay closer attention to hitting the same RNI figure. Pairing iron-rich plant foods with vitamin C — a glass of orange juice alongside a lentil dish, for example — measurably improves how much of it your body actually absorbs.

Sources

1. NHS — Iron deficiency anaemia: symptoms, causes, diagnosis and treatment. nhs.uk/conditions/iron-deficiency-anaemia
2. British Dietetic Association — Iron Food Fact Sheet, Reference Nutrient Intake figures. bda.uk.com/resource/iron-rich-foods-iron-deficiency
3. PMC/NIH — Association between Adiposity and Iron Status in Women of Reproductive Age: Data from the UK National Diet and Nutrition Survey (NDNS) 2008–2019. pmc.ncbi.nlm.nih.gov/articles/PMC11522960
4. EFSA NDA Panel — Scientific Opinion on the substantiation of health claims related to iron. EFSA Journal 2010;8(10):1740. efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2010.1740
5. NHS — Haemochromatosis: overview, symptoms and complications of iron overload. nhs.uk/conditions/haemochromatosis

At Oxford Origins, your wellbeing is our priority, and although we pride ourselves on our expertise in nutrition and supplementation, it's important to acknowledge the individuality of each person. Articles published by Oxford Origins are not intended to treat, diagnose, cure or prevent any disease, or replace the advice of your GP. We always recommend consulting with a healthcare provider if you encounter any health concerns, and we'll always be here to support you so you're never alone on your journey.