Iron Deficiency After 40: Why the Body Often Struggles to Absorb Iron

An underestimated problem

Iron deficiency is often associated with young women or elite athletes – adults in their 40s or 50s are frequently assumed to be at low risk. In reality, the opposite is true: as we age, the likelihood of developing iron deficiency rises significantly.
Studies show that up to one-third of people over 65 have insufficient available iron in their bodies. This is often overlooked because the symptoms are nonspecific and easily attributed to other causes: fatigue, reduced stamina, dizziness, or difficulty concentrating.
Iron deficiency, however, can seriously impair both daily functioning and athletic performance. Adults who remain physically active into midlife and older age represent a particularly under-recognised risk group.

Why physically active adults are especially vulnerable

Anyone over 40 who exercises regularly generally does something very beneficial for their health. Physical activity maintains muscle strength, cardiovascular health, and mental fitness. At the same time, it places additional demands on the body.
Exercise – especially endurance training – increases the need for iron, as the body produces more red blood cells and requires more oxygen transport capacity.
Small amounts of iron are also lost through sweat. During running and other impact sports, the repeated mechanical stress can cause mild destruction of red blood cells. In addition, tiny gastrointestinal bleeds, which become more common with age, can further contribute to iron loss.

None of this would be problematic if the body were able to absorb iron from food or supplements efficiently. Yet this becomes increasingly difficult with age – and here the hormone hepcidin plays a decisive role.

Hepcidin – the “gatekeeper” of iron metabolism

Hepcidin is produced in the liver and regulates how much iron passes from the intestine into the bloodstream. It functions like a gatekeeper: when hepcidin levels are low, the gate remains open and iron from food or supplements is readily absorbed. When levels are high, the gate closes – iron is blocked, remains in the intestine or in storage sites, and is unavailable to the body.

Hepcidin levels tend to rise with age. Several factors contribute to this: mild chronic inflammation that becomes more common with ageing (the phenomenon known as “inflammaging”), certain medical conditions such as kidney or liver dysfunction, and the effects of specific medications.
The result is a so-called functional iron deficiency – iron is present in the body but cannot be used. This form of deficiency is particularly tricky because it is easily missed during routine blood tests.

Exercise further amplifies hepcidin’s effects

It is less widely known that physical exertion itself can increase hepcidin levels. After intense training sessions, production of this hormone rises sharply for several hours. The body reacts to the stress of exercise with a short-lived inflammatory response, and during this period hepcidin blocks iron absorption in the intestine.
Physically active adults and older athletes therefore face a dilemma: their need for iron is higher, yet precisely at the time when they try to replenish it, the body’s ability to absorb iron is at its lowest.

This explains why iron tablets or iron-rich meals taken immediately after training often have little effect. A more effective approach is to take iron several hours later or on a rest day, when hepcidin levels have dropped again.

Why iron tablets often fail

Many people take iron supplements when they feel exhausted or fatigued – often on medical recommendation. Yet experience shows that iron levels in adults over 40 or older patients do not always improve as expected.
Beyond elevated hepcidin activity, several additional factors play a role: as we age, stomach acid production decreases, which hampers the absorption of iron in the intestine. Medications such as proton pump inhibitors (commonly used for heartburn) also reduce iron absorption.
If a chronic inflammatory condition is present, the body may actively block iron – and the tablets remain virtually ineffective. In such cases, intravenous iron is often the better option, though only after careful medical evaluation.

How to recognise iron deficiency

Iron deficiency develops gradually. In everyday life it often manifests as persistent fatigue, difficulty concentrating, headaches, dizziness, pale skin, brittle nails, or frequent infections. Many adults assume these symptoms simply reflect ageing, yet iron deficiency is frequently the underlying cause.

Among physically active adults, iron deficiency often appears as declining performance, reduced training intensity, or longer recovery times. Some notice that they tire earlier at the same workload or feel unusually exhausted after training. A sudden unexplained drop in endurance performance or VO₂peak may also indicate iron deficiency.

Diagnosis: recognising the deficiency correctly

A simple blood test is often not enough to accurately identify iron deficiency. The key laboratory value is ferritin – the body’s iron storage protein – but ferritin can be falsely elevated in the presence of inflammation. For this reason, ferritin should always be assessed together with the inflammation marker CRP and with transferrin saturation (TSAT).
If ferritin is low and CRP is normal, an absolute iron deficiency is present. If ferritin and CRP are elevated but transferrin saturation is low, this usually indicates a functional deficiency – meaning the iron is present but blocked.

For physically active individuals over 40, a detailed diagnostic evaluation is essential before supplementing “just in case”.

How iron deficiency can be treated

The appropriate treatment depends on the underlying cause. If no inflammation or absorption disorder is present, targeted oral iron supplementation can be effective. It is important, however, not to take iron immediately after training. The optimal time window is several hours later or on rest days.
Iron is better absorbed on an empty stomach and when taken together with vitamin C. Coffee, black tea, and dairy products should be avoided at the same time, as they inhibit absorption.

If absorption is significantly impaired or a chronic inflammatory condition exists, intravenous iron may be necessary. This bypasses the intestinal barrier and ensures that the iron reaches the bloodstream directly. In all cases, treatment should be medically supervised to avoid overdosing.

Conclusion

Iron deficiency does not affect only young people – it is equally common in adults over 40, and especially in older athletes.
The combination of age-related inflammation, reduced iron absorption, and exercise-induced increases in hepcidin makes iron management increasingly challenging.

Anyone who remains active in midlife and beyond should therefore monitor their iron status regularly and understand that not every tablet will automatically help. Accurate diagnosis, correct timing, and a treatment strategy tailored to the individual metabolism are crucial.
Only then can we ensure that the body receives iron in a form it can truly use – in the muscles, in the blood, and in daily life.