Iron Deficiency: The Most Common Condition Nobody Takes Seriously
You're exhausted. Not normal tired. You're dragging yourself through the day despite sleeping eight hours. Your hair is falling out in clumps in the shower. You're breathless climbing stairs. You can't concentrate. You feel anxious for no reason. Your hands are always cold.
You go to your GP. They run blood tests. "Your levels are fine," they say. "You're anaemic? No. Your ferritin is 12. That's normal."
Except you're not fine. And technically, medically, your GP is both right and completely missing the point.
This is iron deficiency. The most common nutritional deficiency on the planet. Two billion people worldwide are iron deficient. In the UK, one in four women of reproductive age are iron deficient. And the vast majority of them are told they're fine.
The ferritin scam: why "normal" range is lying to you
Iron is stored as ferritin in your body. When you get a blood test, your GP checks "serum ferritin" and declares you "fine" if it's above 12-15 ng/mL (the lower bound of the "normal" reference range).
Here's the problem: that reference range is based on statistics, not on when people actually feel okay. The lower bound (12-15) was calculated to exclude anaemia, meaning severe iron deficiency. But symptoms of iron deficiency start well above the anaemia threshold. Most people notice fatigue, hair loss, and cognitive issues when ferritin drops below 30-50 ng/mL.
A 2013 study in the Journal of the Academy of Nutrition and Dietetics examined women with ferritin levels between 12-30 (technically "normal" by lab standards) and found they reported significantly higher fatigue, hair loss, and cognitive complaints compared to women with ferritin above 50. Yet their GPs had told them their iron was "fine."
The worst part: once ferritin drops below 15, your body cannot even form new red blood cells properly, even if you haven't crossed into anaemia. You're functionally iron deficient at a cellular level, but the numbers look "normal."
What to do: If you have symptoms of iron deficiency (fatigue, hair loss, breathlessness, brain fog, anxiety) and your GP says your ferritin is "normal," ask for the specific number. Anything below 30 ng/mL warrants investigation and likely supplementation. Aim for ferritin in the 50-150 range (high-normal) if you want to feel good. Don't accept "normal range" as adequate.
Iron deficiency is way more than just fatigue
Everyone knows iron deficiency causes tiredness. What most people don't know is that iron deficiency causes a staggering range of other symptoms, and they're often attributed to entirely different causes.
Restless leg syndrome (that twitching, uncomfortable sensation in your legs that forces you to move them) is often caused by iron deficiency. A 2018 study in Sleep Medicine found that 40% of people with restless leg syndrome had underlying iron deficiency. Most had never been investigated for it.
Hair loss: Iron is essential for the anagen phase (growth phase) of your hair cycle. Without adequate iron, hair prematurely enters the telogen phase (shedding phase). You can lose significant hair without being anaemic. A 2016 study in Dermatology Practical & Conceptual found that hair loss was significantly associated with serum ferritin below 30 ng/mL, even in non-anaemic individuals.
Brain fog and poor concentration: Your brain demands constant oxygen. Iron is crucial for oxygen transport. Iron deficiency reduces oxygen delivery to your brain, making you feel foggy, unable to concentrate, and sometimes anxious. This isn't psychological. It's physiology.
Breathlessness: With low iron, your blood carries less oxygen. Your heart has to work harder to pump the same volume of blood. You become breathless with minimal exertion. Climbing stairs shouldn't make you gasp, if it does and you're iron deficient, this is often the culprit.
Cold hands and feet: Iron is needed for healthy blood vessel function and thermoregulation. Iron deficiency causes poor peripheral circulation. Your hands and feet don't get enough blood flow and feel perpetually cold.
Anxiety: Low iron means low dopamine and serotonin (neurotransmitters synthesised partially using iron as a cofactor). Many people with iron deficiency develop anxiety they never had before. It resolves when iron is replenished.
Pica (cravings to eat non-food items like ice, dirt, or starch): This is a direct symptom of severe iron deficiency. If you're compulsively eating ice or crunching ice obsessively, get your iron checked.
What to do: If you have any of these symptoms in combination, iron deficiency is a likely suspect. Don't just assume you're anxious or depressed or aging normally. Get your iron tested properly (see below) and address it if low.
Iron deficiency versus iron deficiency anaemia: why the distinction matters
Iron deficiency has stages. First, you deplete iron stores (ferritin drops). Then, iron transport becomes impaired (serum iron drops, TIBC rises). Finally, you develop iron deficiency anaemia (haemoglobin drops and you can't make red blood cells).
Most GPs only check haemoglobin. If it's normal, they say your iron is fine. But you can be in stages 1 or 2 (genuinely iron deficient) without yet being anaemic. You have symptoms. Your stores are depleted. But your haemoglobin is still technically normal.
This is why you feel awful but your GP says you're fine. You need a full iron panel, not just a haemoglobin check.
What to do: Ask your GP for a full iron panel: serum iron, serum ferritin, TIBC (total iron binding capacity), and transferrin saturation. Not just haemoglobin. The full picture tells the story of whether you're iron deficient even if anaemia hasn't developed yet.
Why your GP says you're fine when you're not: the system failure
This isn't malice. It's a system designed around safety, not optimisation. GPs are trained to diagnose anaemia because that's dangerous. They're not trained to think about iron status above the anaemia threshold because that's historically been considered "fine."
Additionally, iron supplementation (especially ferrous sulfate, the cheap form GPs prescribe) causes gastrointestinal side effects in many people: constipation, nausea, abdominal pain. So GPs are hesitant to supplement unless anaemia is present. They don't want to prescribe something that makes you feel worse.
The result: people are left with depleted iron stores, feeling terrible, being told they're fine, and left to struggle.
Heavy periods: the #1 cause in young women
In women of reproductive age, heavy or prolonged menstrual periods are the leading cause of iron deficiency. Every month, you're losing iron you're not replacing.
A normal period loses about 30-40mg of iron. Heavy periods (flooding, clots the size of coins, needing to change every 1-2 hours) can lose 100+ mg of iron per cycle. If you're menstruating every 21-35 days and losing that much iron, your stores deplete within months.
The cruel irony: iron deficiency itself can worsen heavy periods (poor clotting, weak blood vessel function), creating a vicious cycle where low iron → heavier periods → lower iron.
Most GPs offer hormonal contraception to manage heavy periods. That helps with bleeding, but it doesn't address the underlying iron deficit you've already accumulated. You need both: treatment of the heavy periods AND iron replenishment.
What to do: If you have heavy periods and any symptoms of iron deficiency (fatigue, hair loss, breathlessness), address the iron deficit while managing the underlying bleeding. This might mean iron supplementation plus hormonal management (pill, progesterone IUD, tranexamic acid). Don't just accept "heavy periods are normal", it's common, but addressable.
Gut absorption issues: coeliac disease and beyond
You can eat plenty of iron and still be deficient if your gut can't absorb it properly. Coeliac disease (autoimmune reaction to gluten) damages the small intestine and impairs mineral absorption. Many people with coeliac disease are iron deficient even before diagnosis.
A 2015 study in Gastroenterology Research and Practice found that 12-20% of people with newly diagnosed coeliac disease had iron deficiency. Many had been told "your iron is fine" for years before proper diagnosis.
Other conditions that impair absorption: Crohn's disease, H. pylori infection, chronic PPI use (acid-reducing medications), and small intestinal bacterial overgrowth (SIBO).
If you've tried iron supplementation and your levels haven't improved after 8-12 weeks, you likely have an absorption problem. This requires investigating gut health, not just taking more iron.
What to do: If you're iron deficient and don't have obvious causes (heavy periods, vegetarian diet without good iron intake), get coeliac screening (tissue transglutaminase antibodies). If negative but symptoms persist, consider H. pylori testing, evaluation for Crohn's disease or SIBO, and review any acid-reducing medications you're taking.
Which iron supplements actually work (and which are useless)
Not all iron supplements are equal. Absorption varies dramatically depending on the form.
Iron sulfate: Cheap, widely prescribed, absorbed reasonably well. Problem: gastrointestinal side effects in 20-30% of people (constipation, nausea, abdominal pain). These side effects cause poor compliance, people stop taking it because it makes them feel worse.
Iron glycinate/iron bisglycinate: Chelated form (iron bonded to the amino acid glycine). Better absorbed, better tolerated, fewer GI side effects. More expensive. Worth it.
Iron polysaccharide: Gentler, minimal GI side effects. Absorption is sometimes lower but many people do well with it.
Ferrous fumarate: Middle ground. Reasonable absorption, moderate GI side effects. Less problematic than sulfate but not as good as chelated forms.
A 2019 meta-analysis in Nutrients comparing iron forms found that chelated forms (glycinate, threonate) had better overall efficacy, better tolerability, and better compliance rates compared to simple salts.
What to do: If your GP prescribes ferrous sulfate and you experience nausea or constipation, ask for an alternative. Iron glycinate (15-25mg elemental iron daily) is gentler and better absorbed despite higher cost. Take iron with vitamin C (orange juice, berries) to enhance absorption. Don't take iron with coffee, tea, or calcium supplements, they impair absorption.
The every-other-day dosing study: why daily isn't always better
A landmark 2015 study by Moretti published in Haematologica compared daily versus every-other-day iron supplementation. The result was counterintuitive: every-other-day dosing produced better absorption and better haemoglobin improvement over eight weeks compared to daily dosing.
Why? When you take iron daily, you continuously suppress hepcidin (a hormone that controls iron absorption). This actually reduces your body's ability to absorb subsequent doses. With every-other-day dosing, hepcidin levels normalise between doses, allowing better absorption on dosing days.
This suggests that taking your iron supplement every other day, rather than daily, might actually be more effective. It's counterintuitive but evidence-based.
What to do: Try every-other-day iron dosing for 8-12 weeks as a trial. Take your supplement one day, skip a day, take it the next day, and so on. Retest ferritin after 8-12 weeks and compare to previous supplementation patterns. Many people get better results with less frequent dosing and fewer side effects.
Iron infusions: when and why
If you have severe iron deficiency, absorption problems, or cannot tolerate oral supplementation, IV iron infusions are an option. They bypass the gut entirely and rapidly replenish iron stores.
Iron sucrose or iron carboxymaltose infusions are well-tolerated and effective. A single infusion can deliver 500-1000mg of iron, equivalent to several months of oral supplementation.
They're typically reserved for severe deficiency or absorption disorders, but they're worth knowing about if you're struggling with oral supplements.
What to do: If you're severely anaemic (haemoglobin below 7), have absorption disorders, or cannot tolerate oral iron despite multiple attempts with different formulations, ask your GP about iron infusions. Private options are available if NHS waiting lists are long.
What to test and what numbers to aim for
Full iron panel: Serum ferritin, serum iron, TIBC, transferrin saturation, and haemoglobin. Don't settle for haemoglobin alone.
Serum ferritin target: Minimum 30 ng/mL to avoid symptoms. Optimal 50-150 ng/mL for feeling good. Above 150 is potentially excessive and should be investigated (iron overload is rare but possible).
Haemoglobin: Women: above 12 g/dL. Men: above 13.5 g/dL. Below these ranges indicates anaemia requiring investigation.
Retest timing: After starting supplementation, retest ferritin after 8-12 weeks. Adjust dosing based on response. Some people need higher doses or longer supplementation to fully replenish stores.
Additional testing if deficient: Coeliac screening (tissue transglutaminase antibodies), B12 and folate levels (often co-deficient), and if applicable, assessment for heavy periods or gastrointestinal bleeding.
Tired of being told you're fine when you're not? Get a proper assessment.
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