Iron and Women's Health: Deficiency and Ferritin

Iron deficiency is the most common nutritional deficiency in the world, and women of reproductive age carry it far more often than men. The reason is physiological: every menstrual cycle and every pregnancy draws iron out of the body, and an ordinary diet doesn't always replace it. The key marker of stores is ferritin — the WHO puts the deficiency threshold at 15 µg/L, but symptoms often appear earlier, at the "low end of normal." Here is why that happens, how to read your labs, and when supplements are justified versus an unnecessary risk.

Why women are at higher risk#

An adult body loses iron mostly passively — through shed gut and skin cells, roughly 1–2 mg a day. In women, menstrual blood loss is added on top. An average cycle loses 30–40 mL of blood; heavy periods can mean 80 mL or more, equivalent to an extra 15–30 mg of iron a month. This is why the daily iron requirement for women of reproductive age is higher than for men: about 18 mg versus 8 mg.

Heavy menstrual bleeding (menorrhagia) is an underappreciated cause of chronic deficiency. A woman can live for years with depleted stores, blaming the fatigue on stress and poor sleep. A non-hormonal intrauterine device can increase blood loss, whereas hormonal contraception and levonorgestrel-releasing systems usually reduce it.

Pregnancy is a separate, powerful drain. Blood volume expands, the growing fetus and placenta need iron, and the total "cost" of a pregnancy is around 1000 mg of iron. Even a woman who enters pregnancy with normal stores is often deficient by the third trimester. Breastfeeding uses iron moderately, but on top of already-low stores it still matters.

Symptoms: from obvious to invisible#

The classic signs of iron-deficiency anaemia are pallor, marked weakness, breathlessness on exertion and a racing heart. But long before anaemia, at the latent (hidden) deficiency stage, symptoms can already lower quality of life:

• constant fatigue that sleep doesn't fix;
• reduced exercise tolerance, "no energy" for training;
• hair shedding, brittle nails;
• trouble concentrating, "brain fog";
• feeling cold, cold hands and feet;
• unusual cravings to chew ice or non-food items (pica);
• restless legs.

The problem is that these symptoms are non-specific and easily blamed on anything. That's why the decision should rest on a blood test, not on how you feel.

Читайте также: The menstrual cycle and training: how the phases affect load and recovery

Ferritin and latent deficiency#

Ferritin is the protein that stores iron, and its blood concentration reflects the size of your reserves. It is the most sensitive early marker — it drops first, while haemoglobin is still normal. That state, low ferritin with normal haemoglobin, is what latent iron deficiency means. Anaemia develops later, once the stores are empty and there isn't enough iron to make red blood cells.

WHO thresholds (2020):

Marker	Value	What it means
Ferritin, adults	< 15 µg/L	Depleted iron stores (WHO)
Ferritin, clinical threshold	< 30 µg/L	Often already depleted; many clinicians treat
Ferritin with inflammation	< 70 µg/L	May mask deficiency
Haemoglobin, non-pregnant women	< 120 g/L	Anaemia (WHO)
Haemoglobin, pregnant	< 110 g/L	Anaemia in pregnancy (WHO)

An important subtlety: ferritin is an acute-phase protein. With infection, a chronic-disease flare, or obesity, it rises independently of iron stores. So a "normal" ferritin against a background of inflammation does not rule out deficiency. The British Society for Haematology recommends reading ferritin together with C-reactive protein (CRP) and, when in doubt, checking transferrin saturation.

Heme and non-heme iron#

Dietary iron comes in two forms, and they are absorbed very differently.

Heme iron is found in meat, poultry, fish and seafood. It comes from animal haemoglobin and myoglobin, absorbs well (15–35%) and depends little on the rest of the meal.

Non-heme iron is the iron in plants (beans, tofu, spinach, grains, seeds) and fortified foods. Its absorption is lower (2–20%) and heavily influenced by what it's eaten with. This is why vegetarians and vegans need to be more deliberate about iron: the diet may contain plenty on paper, but less of it is absorbed.

Food	Iron per 100 g	Type
Beef liver	~6.5 mg	heme
Beef	~2.7 mg	heme
Oysters	~5 mg	heme
Cooked lentils	~3.3 mg	non-heme
Tofu	~2.7 mg	non-heme
Cooked spinach	~3.6 mg	non-heme
Pumpkin seeds	~8 mg	non-heme

What helps and what hinders absorption#

Non-heme iron absorption is something you can steer with food combinations.

Helps:

• Vitamin C — converts iron into a more absorbable form. Bell pepper, citrus, kiwi, broccoli or berries in the same meal as plant iron noticeably raise uptake.
• Meat, fish, poultry — the so-called "meat factor" enhances absorption of non-heme iron from plants eaten alongside.

Hinders:

• Coffee and tea — polyphenols (tannins) bind iron. A cup of tea with a meal can cut non-heme iron absorption by tens of percent.
• Calcium — from dairy and supplements competes with iron. Don't wash down iron-rich meals with milk.
• Phytates — in whole grains and legumes; soaking, sprouting and fermentation (sourdough) partly neutralise them.

The practical takeaway: if you're deficient, separate coffee and tea from iron-rich food and supplements by at least 1–2 hours, and pair plant iron with a source of vitamin C.

When supplements are needed — and why not "just in case"#

Iron supplements effectively correct deficiency, but they are a medicine, not a preventive vitamin. There is one indication — lab-confirmed deficiency (low ferritin, and if needed low transferrin saturation), ideally with the cause identified.

Key principles of use (to discuss with a clinician):

• Ferrous iron salts are the usual choice; current evidence suggests doses around 40–80 mg elemental iron every other day are often absorbed at least as well as large daily doses, and are better tolerated.
• Take on an empty stomach or with vitamin C, away from coffee, tea and calcium.
• Common side effects are constipation, nausea, dark stools and stomach discomfort; if intolerable, the form or schedule is changed.
• Ferritin recovers slowly: a course usually runs several months, with a follow-up test.

Pregnancy is a separate case: the Cochrane review shows that routine iron reduces maternal anaemia and deficiency, but the dose and the need are set by a clinician based on labs — not "all pregnant women take iron."

Читайте также: Iron and ferritin: how to read your labs and choose a supplement

Myths and common mistakes#

A lot of half-truth has built up around iron, leading women to either overload on supplements or ignore a deficiency for years.

"I eat spinach, so I'm getting enough iron." Spinach does contain iron, but it's non-heme, and its oxalates further reduce absorption. The "iron-rich spinach" legend grew in large part from an old calculation error. Spinach alone won't fix a deficiency.

"No anaemia means everything is fine." Haemoglobin falls last. By the time it drops below normal, stores have long been empty, and a latent deficiency with fatigue and hair loss may have dragged on for months. This is exactly why ferritin is more informative than haemoglobin alone.

"The iron in my multivitamin will handle it." "Women's" formulas usually contain little iron, and it sits next to calcium and zinc that compete for absorption. For treating a confirmed deficiency such doses are typically inadequate, and "just in case" they aren't needed.

"The bigger the dose, the faster I'll recover." Large daily doses raise the hormone hepcidin, which temporarily blocks absorption of the next portion. That's why an alternate-day schedule with a moderate dose often works just as well and is better tolerated — but the specific regimen is set by a clinician.

"Dark circles and pale skin definitely mean low iron." These are possible but non-specific signs. Only a blood test can confirm iron deficiency — not a visual check or self-diagnosis from symptom lists online.

What to do#

1. Don't guess from symptoms — get tested. At minimum: a full blood count (haemoglobin) and ferritin; with inflammation or borderline results, add CRP and transferrin saturation.
2. Assess blood loss. If periods are heavy (soaking a pad or tampon more than once every 2 hours, clots, cycles longer than 7 days), raise it with a gynaecologist — the cause of deficiency may be exactly there.
3. Tune your diet. Heme sources if you eat meat or fish; for plant iron, add vitamin C to the same meal and keep coffee and tea away.
4. Supplements only after a test and with a clinician. Don't put yourself on iron "just in case," and don't give iron tablets to children without an indication.
5. Track the trend. After starting correction, retest ferritin in 2–3 months to confirm stores are rebuilding.

Iron is a case where both deficiency and excess are harmful, and "how you feel on average" is misleading. So decisions are made on the numbers: ferritin and haemoglobin, interpreted by a clinician in the context of your physiology.