Why are your iron stores low, and what is keeping them low?

You wake up tired, struggle to get through the afternoon and feel as though your energy never quite returns. A blood test reveals low ferritin, and the explanation seems straightforward: your iron stores are depleted, so you start taking iron.

For some people, that makes a real difference. For others, ferritin barely rises, digestive side effects make supplementation difficult, or the result improves only to fall again a few months later.

Fatigue has many possible causes. But when low iron stores are confirmed, replacing iron is only one part of the assessment. The other is understanding why those stores became depleted. Sometimes the explanation involves heavy periods or insufficient intake. Sometimes it begins in the stomach, with an infection such as H. pylori.

Low ferritin can matter before anaemia develops

Ferritin is a protein that stores iron. A low blood ferritin usually indicates depleted iron reserves, even when haemoglobin, the protein that carries oxygen in red blood cells, remains within the laboratory range. Iron deficiency can therefore develop before anaemia becomes apparent.

This distinction matters when someone feels persistently tired but has been told their blood count is normal. In a randomised trial of menstruating women with fatigue and low ferritin, iron supplementation reduced fatigue more than placebo even though the participants did not have anaemia. The result supports recognising depleted iron stores as a possible contributor to fatigue, rather than relying on haemoglobin alone.

The next question is what caused the depletion, particularly when ferritin repeatedly falls or does not respond as expected.

Why another iron supplement may leave the cause unresolved

Low ferritin can reflect too little dietary iron, increased requirements, ongoing blood loss or impaired absorption. Heavy menstrual bleeding, blood donation, gastrointestinal bleeding and coeliac disease are among the possibilities. Several factors can be present together.

A doctor may prescribe iron, while a functional medicine practitioner may recommend a different formulation, a higher dose or another supplement to support absorption. These approaches can help replenish stores, but neither establishes why the deficiency developed if the investigation stops there.

Changing the product will not explain an inflamed stomach or continuing blood loss. Replacing iron and investigating the cause belong in the same treatment plan.

H. pylori: a stomach infection that can remain unnoticed

Helicobacter pylori is a bacterium that colonises the stomach. A large 2023 review estimated global prevalence at about 43% from 2011 to 2022, although rates vary considerably between populations. Many infected people have no obvious symptoms.

People often acquire the infection in childhood, and it can persist for decades. It may spread through contact with infected saliva, vomit or stool, and contaminated food or water can also play a role. An infection discovered in adulthood may therefore have been present long before digestive symptoms appeared.

H. pylori survives within the mucus protecting the stomach lining. It produces an enzyme called urease, which helps neutralise acid immediately around the bacteria. This local protection, together with its ability to evade effective immune clearance, allows inflammation to continue. Some people develop upper abdominal discomfort, nausea or ulcers, while others remain unaware of the infection.

How stomach inflammation can affect your iron stores

The stomach helps prepare nutrients for absorption further along the digestive tract. H. pylori related inflammation can interfere with iron absorption. If longstanding inflammation causes loss of stomach glands, acid production can fall, making nonhaem iron, including iron from plant foods, harder to absorb. Ulcers can also cause blood loss, sometimes without obvious visible bleeding.

This creates a situation in which someone may eat iron containing foods yet struggle to maintain their stores. Supplementation may raise ferritin temporarily, while ongoing losses or impaired absorption continue to undermine progress.

H. pylori is one possible explanation for this pattern. Its presence needs to be established through testing, and other causes of iron deficiency still belong in the assessment.

Testing needs to identify active infection

A routine blood count or ferritin measurement cannot establish whether H. pylori is present. A urea breath test or stool antigen test can identify active infection. Blood antibodies may remain positive after the bacteria have cleared, so they are unsuitable for confirming eradication.

Understanding why your ferritin keeps falling

If low ferritin contributes to your fatigue, restoring iron stores may improve how you feel. Lasting progress also depends on identifying anything that continues to deplete those stores, whether that is heavy bleeding, insufficient intake, coeliac disease, H. pylori or another stomach condition.

The question extends beyond which iron supplement to choose: why are your iron stores low, and what is keeping them low? Answering that question can change both the investigation and the treatment.

At my functional medicine practice, I look at digestive symptoms, nutrition, lifestyle and previous results together to help understand recurring deficiencies. Explore personalised functional medicine support or book a free discovery call to discuss your concerns.