Article Series

  1. Iron - Health Benefits - Improving Iron Absorption
  2. Iron Requirement - How Much Is Needed Per Day
  3. Iron Deficiency: Symptoms, Causes, Consequences, Treatment

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Iron Deficiency: Symptoms, Causes, Consequences, Treatment

Iron Deficiency: Symptoms, Causes, Consequences, Treatment
Table Of Contents
  1. Risk Groups
  2. Causes of iron deficiency
  3. Symptoms of Iron Deficiency
  4. Consequences of Iron Deficiency
  5. Diagnosing Iron Deficiency
  6. Treatment
  7. Preventive Measures

Iron serves numerous important functions in the body. It is involved in the transportation of oxygen in the body as a component of the red blood pigment (hemoglobin). Additionally, iron is part of the red muscle pigment (myoglobin) which is necessary for storing oxygen in cells. Oxygen is needed for the body's energy production. The brain also has a high demand for oxygen. Therefore, without iron, there are not only physical limitations but also cognitive impairments.

An iron deficiency (sideropenia) is characterized by depletion of the body's iron reserves and limited iron supply through diet. It occurs equally frequently in both omnivores and vegans 1 2 3. According to a large study from 2003, vegans have the highest iron intake levels 4. Iron deficiency is a global problem 5.

Risk Groups

Individuals who already have a higher daily iron requirement are considered at risk. This primarily includes infants, children, adolescents, and especially women of childbearing age who lose iron due to regular blood loss 6 7 8.

Pregnant women (due to the rapid growth of the placenta and fetus) and lactating women also face a higher risk of iron deficiency 9.

Athletes and individuals who are physically active in their professions also have a higher iron requirement. Female athletes, in particular, have a significantly higher risk of iron deficiency due to intense training 10. Endurance athletes, including female athletes, may also be affected by iron deficiency 11.

People who donate blood also run the risk of iron deficiency. The body loses a significant amount of iron through blood donation 12. Therefore, it is advisable to donate blood at longer intervals (approximately 3 times a year).

Another at-risk group includes individuals with liver disorders or gastrointestinal tract problems. Consequences can include inadequate iron storage in the liver or reduced iron absorption from food 13.

Even older individuals, whose ability to absorb iron from food decreases with age, can suffer from a deficiency 14.

Dialysis treatment can contribute to iron loss in individuals with kidney failure 15.

Obese individuals have a significantly higher susceptibility to iron deficiency 16 17.

Patients with chronic heart failure are also frequently affected by iron deficiency. 18 19.

Causes of iron deficiency

An unbalanced diet or excessive consumption of processed products can quickly lead to iron deficiency. It should also be noted that certain dietary components, medications, and alcohol can impair iron absorption. 20. Medications that increase stomach pH (e.g., antacids, proton pump inhibitors, histamine H2 blockers) restrict iron absorption. 21.

However, most often there is a disturbance in the digestive tract (infections such as Whipple's disease), stomach ulcers, or chronic bowel diseases such as celiac disease, ulcerative colitis, or Crohn's disease, which can lead to reduced absorption of iron from food 22 23. In this context, a reduced liver storage capacity for iron can also be the cause of iron deficiency.

Chronic bleeding can be responsible for iron deficiency. For example, hematuria can be the cause of a deficiency. Hematuria describes the increased excretion of red blood cells in the urine. Iron can also be lost to the body through bleeding hemorrhoids. Other causes that can result in bleeding include colon cancer, uterine cancer, and intestinal polyps 24.

Even with the switch to a vegan diet and with an overly restrictive diet, there may be a risk of iron deficiency because iron from plant sources (non-heme iron) is less readily absorbed 25. However, the body adapts over time and improves absorption from food. Therefore, a higher iron intake is recommended during the transition as well. A German study with 75 women found iron deficiency in 40% of younger women under 50 years and 12% of older women 26. In an Australian study with a total of 50 vegetarian and vegan women, they had an average serum ferritin level (ferritin being the protein that stores iron) of 25 μg/L (± 16.2) 27. A ferritin level below 12 μg/L indicates iron deficiency. Apart from that, iron consumption with a vegan diet is higher compared to other dietary forms 28.

Through sweat, the body loses iron. 29. Prolonged sweating, such as during exercise or occupational activities, can also be the cause of a deficiency. Additionally, repeated impact on hard surfaces can destroy red blood cells, leading to iron loss. 30.

In overweight individuals, iron deficiency may occur due to inadequate iron intake or a higher blood volume (total blood volume in the body), which requires more iron. 31. Furthermore, chronic inflammation is associated with higher levels of hepcidin in overweight individuals. Hepcidin reduces iron absorption in the intestine.

Cow's milk can be a cause of iron deficiency in infants and toddlers. 32. It leads to increased excretion of iron.

In addition, a protein deficiency, which is rare, can worsen iron deficiency 33. The reason lies in the impairment of iron absorption, transport, and storage.

Symptoms of Iron Deficiency

An iron deficiency can be classified into three stages:

  1. Prelatent iron deficiency (depletion of stored iron; decrease in serum ferritin levels)
  2. Latent iron deficiency (depletion of iron reserves; decreased transport iron levels; reduced iron levels in bone marrow and blood serum)
  3. Manifest iron deficiency (reduced hemoglobin synthesis; formation of smaller and fewer red blood cells) with distinct symptoms of iron deficiency anemia (anemia = colloquially known as blood deficiency)

Prelatent and latent iron deficiency do not necessarily lead to symptoms 34.

However, a short-term iron deficiency can cause the following early symptoms:

  • Headaches
  • Difficulty concentrating
  • Irritability

Iron deficiency can occur with or without anemia. When iron deficiency worsens (manifest iron deficiency), the following symptoms of iron deficiency anemia are usually visible: 35 36 37:

  • Fatigue/exhaustion due to lack of oxygen
  • Decreased muscle function with decreased performance
  • Pale and dry skin
  • Shortness of breath
  • Rapid heartbeat and heart rhythm disturbances, as the heart has to work harder to pump enough oxygen to the cells due to lower hemoglobin levels
  • Drop in body temperature, associated with cold hands and feet
  • Impaired immune system with higher susceptibility to infections
  • Cracked corners of the mouth (angular cheilitis)
  • Dry mouth due to reduced saliva flow
  • Atrophy of the tongue papillae (smooth, shiny red tongue)
  • Irritated mucous membranes
  • Brittle fingernails
  • Hair loss/alopecia
  • Constipation
  • Dizziness

Consequences of Iron Deficiency

Manifest iron deficiency is also known as iron deficiency anemia. In this condition, the body produces fewer and smaller red blood cells. The body has too few healthy red blood cells, resulting in less oxygen being delivered to the cells, which can lead to the symptoms mentioned above.

A deficiency not only negatively affects the performance of athletes (impaired muscle function) 38. Reduced blood production leads to less oxygen being transported to and within the muscles. Ultimately, less energy is released in the cells, resulting in decreased performance. The consequences include early muscle fatigue, reduced mobility, and prolonged recovery times after training.

In rare cases of severe iron deficiency, it can also lead to Plummer-Vinson syndrome. 39 In this condition, certain proteins cannot be produced due to a lack of iron. As a result, mucosal defects in the mouth and throat, difficulty swallowing, and tongue burning are often typical symptoms.

Studies suggest a possible link between iron deficiency and an increased risk of heart attacks. 40 The research found that iron deficiency increases the stickiness of blood platelets. This leads to platelet aggregation, resulting in blood clot formation (thrombosis) and can be a trigger for heart attacks.

The thyroid function can be negatively affected by a deficiency, leading to a reduced release of the important thyroid hormone triiodothyronine (involved in energy metabolism) 41.

Above all, pregnant and lactating mothers should ensure an adequate intake of iron to avoid developmental impairments in the child. (Source: 42.) Anemia in pregnant women can lead to premature birth, low birth weight in infants, and increased child mortality. (Source: 43.) Other consequences include delayed psychomotor development in infants, reduced cognitive performance, and negative mood states. (Sources: 44 and 45.)

Furthermore, iron deficiency may potentially increase the risk of manganese accumulation in the brain, which is associated with Parkinson's disease 46.

Some individuals develop Restless Legs Syndrome (RLS) due to iron deficiency 47. This condition leads to an uncomfortable sensation in the legs and a strong urge to move them. Additionally, people with RLS also experience sleep disturbances.

Diagnosing Iron Deficiency

An iron deficiency is determined through a blood test conducted by a doctor. The following values provide information about an impending deficiency or iron deficiency: 48 49 50 51:

Normal iron levels Serum ferritin:
Female: 12-150 ng/ml
Male: 12-300 ng/ml

Iron levels: 8.0-26 μmol/l
Depleted iron levels Serum ferritin:
< 12-15 µg/l (= < 12-15 ng/ml)
Early functional iron deficiency
(suboptimal iron supply to bone marrow and other tissues;
hemoglobin levels are still normal)
Transferrin saturation < 16%
(normal range: 16-45%)
Iron-deficiency anemia
(measurable deficiency of red blood cells)
Hemoglobin concentration:
Female: < 115 g/l
Male: < 135 g/l

Hemoglobin concentration according to WHO:
Female: < 120 g/l (7.4 mmol/l)
Male: < 130 g/l (7.7 mmol/l)

Mean corpuscular volume < 80 fL


Iron deficiency can only be permanently avoided by eliminating the underlying cause. Therefore, it is important to identify the cause in order to initiate the appropriate therapy. If the cause is not eliminated, the initial symptoms will reappear sooner or later.

Corresponding treatment, especially for manifest iron deficiency, is usually carried out through the oral intake of iron supplements, which should be discussed with a doctor 52. Iron supplements are administered in the form of iron sulfate. In most cases of iron deficiency anemia, iron sulfate is administered at a dosage of 325 mg, taken three times a day for a period of 6 to 8 weeks 53 54. A low-dose iron supplement is sufficient to increase iron stores and optimize hemoglobin in cases of nutrition-related iron deficiency in healthy individuals 55. Self-treatment can lead to health damage as the dosages depend on individual factors such as body weight and iron status!

Additionally, consuming foods rich in vitamin C or supplementing with ascorbic acid can contribute to improving iron status 56. For example, researchers provided strict vegetarians with 500 mg of vitamin C twice daily after meals for a period of two months to increase hemoglobin and serum iron levels 57. Hemoglobin levels increased by 8%, serum iron by 17%, and transferrin saturation by 23%. Ultimately, the scientists concluded from their results that vitamin C is more effective in increasing iron status than iron supplementation. In a study involving vegetarian children suffering from anemia, vitamin C also significantly improved iron levels and contributed to their recovery 58. The children received 100 mg of ascorbic acid twice daily for a period of 60 days. Additionally, the treatment recommended avoiding iron-rich foods high in phytates (mainly found in grains, nuts, and seeds) and tannins (tea). Further factors that impede iron absorption can be found here.

In severe cases, iron infusions (in the form of iron sucrose) are necessary if iron deficiency cannot be resolved through diet, the body is chronically bleeding, or the hemoglobin level is less than 6 g/dL (60 g/L). 59 60 Blood transfusions are also possible.

Preventive Measures

Naturally, consuming iron-rich foods (table) is the first preventive measure. Additional measures to improve iron absorption include consuming vitamin C-rich foods (refer to the vitamin C foods table) and carotenoids simultaneously, which can enhance iron absorption from food.

Preventive intake of iron supplements is not recommended and should be discussed with a doctor.