Iron Deficiency: Why Normal Blood Test Results Can Be Misleading
Laura Chrobok 22.06.2026
Tired, exhausted, unable to concentrate. Your hair becomes thinner, your stamina declines and even adequate sleep seems to make little difference. In such situations, many people assume that stress, lack of sleep or a particularly demanding lifestyle must be the cause. In reality, something entirely different may be responsible: iron deficiency. Symptoms can occur even when standard blood test results still appear largely normal.
Today, we take a closer look at the functions of iron, common signs of deficiency and why a laboratory marker known as ferritin often deserves far more attention.
What Is Iron and Why Does the Body Need It?
Iron (ferrum in Latin) is an essential mineral. (Other indispensable minerals for the human body include magnesium and zinc.) The body cannot produce iron on its own and must therefore obtain it regularly through food.
Iron is best known for its role in oxygen transport. The mineral is a component of haemoglobin, the red blood pigment responsible for carrying oxygen from the lungs to organs and tissues.
In addition, iron is involved in numerous metabolic processes and is required for energy production, various enzymes and normal cognitive function.
Every cell in the body requires oxygen to generate energy. When iron is lacking, haemoglobin production may be impaired. As a result, less oxygen is transported throughout the body, which can affect both physical and mental performance. It is therefore hardly surprising that fatigue and exhaustion are among the most common symptoms of iron deficiency.
Iron is also required for numerous enzymatic processes directly involved in energy metabolism (National Institutes of Health, 2024).
What Are Typical Signs of Iron Deficiency?
Symptoms often develop gradually and can appear rather nonspecific, which is why they are not always associated with iron deficiency.
Common signs include:
· fatigue
· exhaustion
· reduced physical performance
· concentration problems
· dizziness
· headaches
· pale skin
· hair loss
· brittle nails
· shortness of breath during physical exertion
(Mayo Clinic, 2024).
Iron deficiency is one of the most common nutrient deficiencies worldwide (World Health Organization, 2023).
Empty Iron Stores — Why Do Many People Learn About Ferritin Only Late?
The reason is simple: as long as haemoglobin and other standard blood markers remain within normal ranges, iron deficiency may not immediately be considered.
Ferritin serves as the body's iron-storage protein and can provide valuable information about how well iron reserves are replenished. However, these stores may already be significantly depleted and associated with symptoms long before classic anaemia develops.
A review by Camaschella describes iron deficiency without anaemia as a clinically relevant condition that is frequently overlooked (Camaschella, 2019).
Why Are Women Particularly Affected?
Women are among the groups most at risk of iron deficiency. The main reason is regular blood loss during menstruation. Heavy menstrual bleeding can substantially reduce iron stores over time.
Iron requirements also increase significantly during pregnancy and breastfeeding.
Additional risk factors include:
· vegetarian or vegan diets
· endurance and competitive sports
· chronic inflammatory bowel diseases
· coeliac disease
· certain gastrointestinal disorders
(NIH, 2024).
Obtaining Iron Through Food — Which Foods Are Good Sources?
Foods particularly rich in iron include:
o liver
o beef
o oysters
o lentils
o chickpeas
o beans
o pumpkin
o oats
o whole grains.
In general, iron from animal-based foods is absorbed more efficiently than iron from plant sources. Vitamin C can further enhance absorption, whereas coffee and black tea may reduce it (NIH, 2024).
Can Iron Supplements Help Correct a Deficiency?
If iron deficiency is genuinely present, iron supplements may be beneficial.
However, iron should not be taken simply on suspicion.
Possible side effects of supplementation include:
· nausea
· abdominal pain
· constipation
· diarrhoea
· dark stools
(Mayo Clinic, 2024).
Whether supplementation is appropriate should ideally be determined together with a healthcare professional and based on laboratory findings.
Conclusion: Iron Deficiency Is Often a Hidden Problem
Most people associate iron deficiency with severe anaemia. However, the scientific literature paints a more nuanced picture: symptoms may already occur before classic iron-deficiency anaemia develops.
For this reason, persistent fatigue, exhaustion, concentration problems or reduced performance should not prompt attention solely to iron levels. Ferritin deserves particular consideration. This laboratory marker can provide important clues about the body's iron reserves — and it is often here that iron deficiency begins long before it becomes obvious.
Because of its role in oxygen transport, energy production and physical performance, iron remains one of the most important minerals for human health.
FAQ — (Additional) Frequently Asked Questions About Iron
1. Which substances can reduce iron absorption?
Certain substances may reduce iron absorption in the intestines, including:
o tannins found in black tea, green tea and, to some extent, coffee
o phytates found in whole grains, bran, legumes, nuts and seeds
o oxalates found in foods such as spinach, Swiss chard and rhubarb
o larger amounts of calcium, for example from dairy products or calcium supplements
(Hurrell & Egli, 2010).
2. How long does it usually take to replenish depleted iron stores?
This depends on the cause and severity of the deficiency as well as the chosen treatment approach. In general, laboratory values may begin to improve within a few weeks, while complete replenishment of iron stores can take several months (Camaschella, 2019).
3. Which groups of people may have increased iron requirements?
o women with heavy menstrual bleeding
o pregnant women
o breastfeeding women
o children and adolescents during periods of growth
o endurance and competitive athletes
o people following vegetarian or vegan diets
o individuals with chronic blood loss or certain gastrointestinal disorders.
As is often the case, the actual situation must always be assessed on an individual basis (NIH, 2024).
Further information on minerals and many other topics can be found not only on our blog, but also in our “Medizinskandale” book series and the “Codex Humanus”, the fifth volume of which was recently published. Feel free to visit our online shop.
Sources:
· National Institutes of Health (NIH), Office of Dietary Supplements (2024): “Iron – Fact Sheet for Health Professionals.”
· Mayo Clinic (2024): “Iron Deficiency Anemia – Symptoms and Causes.”
· World Health Organization (WHO) (2023): “Anaemia.”
· Camaschella, C. (2019): “Iron Deficiency,” Blood.
· Hurrell, R.; Egli, I. (2010): “Iron Bioavailability and Dietary Reference Values,” American Journal of Clinical Nutrition.