Heavy periods and low iron: why so many women have low ferritin

Low iron is one of the most common findings in women's blood tests. Many women have lived with it for so long that the tiredness, the hair shedding and the breathlessness on the stairs feel normal. Often the cause is simple: every period takes some iron with it, and heavy periods take a lot.

Where your iron goes

Most of the iron in your body sits inside haemoglobin, the protein in red blood cells that carries oxygen. The rest is stored, mainly in the liver, as ferritin. When you lose blood, your body replaces the red cells by drawing on those stores. If you lose more each month than your diet can put back, the stores slowly run down.

This happens in stages. First the stores empty while haemoglobin stays normal. Only once the stores are close to gone does haemoglobin start to fall. That is why a normal blood count on its own does not rule out an iron problem, and why the Well Woman panel measures ferritin and full iron studies alongside it.

What counts as a heavy period

There is no single number, because nobody measures their blood loss. Doctors look for bleeding that affects your daily life. Signs that your periods may be heavier than they should be include:

• Soaking through a pad or tampon every hour or two.
• Needing to change protection during the night, or waking with leaks.
• Passing clots larger than a coin.
• Periods that last longer than seven days.
• Planning your week around your period, or avoiding work or exercise because of it.

Heavy periods are common, but they are worth discussing with a doctor. Causes include fibroids, polyps, thyroid problems, bleeding disorders and the hormonal changes of perimenopause. Many of these are treatable, and treating the bleeding is the most reliable way to stop the iron loss.

How to read ferritin

Ferritin is the best single blood marker of your iron stores. LifePrint uses the World Health Organization's 2020 guideline on ferritin. For adults, a ferritin below 15 ug/L means iron deficiency. Results from 15 to 30 ug/L sit in LifePrint's grey zone: not yet deficient by the WHO definition, but low stores that are worth attention, especially if you have symptoms or heavy periods.

There is one important catch. Ferritin also rises with inflammation, infection, liver disease and alcohol. A ferritin that looks normal can hide a real deficiency if something else is pushing it up. The WHO guideline allows for this by using a higher cut-off of 70 ug/L when inflammation is present. This is why your report reads ferritin together with hs-CRP, the inflammation marker in your panel.

When low iron becomes anaemia

Anaemia means your haemoglobin has fallen below the level your body needs. Under the WHO's 2024 guideline on haemoglobin cut-offs, a non-pregnant adult woman is anaemic below 12.0 g/dL. The WHO grades it as mild from 11.0 to 11.9 g/dL, moderate from 8.0 to 10.9 g/dL and severe below 8.0 g/dL. Severe anaemia is flagged on your LifePrint report as needing prompt medical attention.

Iron deficiency anaemia often shows other clues in the blood count. The red cells tend to become smaller and paler, which appears as a low MCV. These changes help a doctor tell iron deficiency apart from other causes of anaemia, such as low B12 or folate.

Other reasons for low iron

Periods are the most common cause in women of reproductive age, but not the only one. Pregnancy and breastfeeding use a lot of iron. Plant-based diets can be low in easily absorbed iron. Regular blood donation, heavy endurance training and conditions that affect absorption, such as coeliac disease, all play a part. Blood loss from the gut is less common but important, particularly if your periods have stopped, so unexplained low iron should always be looked into by a doctor.

What to do with a low result

Speak to a doctor about both the result and the cause. Iron can be replaced with tablets or, in some cases, an infusion, but the right form and amount depend on how low you are and why. Taking iron without a clear reason is not harmless, because too much iron builds up in the body. A repeat test after treatment shows whether your stores are recovering.

Your LifePrint report explains where each iron marker sits and how urgently to follow up. It is health information, not a diagnosis, so take any flagged result to a registered healthcare practitioner.