Iron Deficiency & Iron-Deficiency Anemia:
Symptoms, Causes & Treatment

At a glance

FrequencyThe most common nutritional deficiency worldwide; women of childbearing age, children, and older people are particularly often affected
DefinitionIron deficiency = reduced iron stores; iron-deficiency anemia = iron deficiency with hemoglobin dropping below the normal value
Main symptomsFatigue, exhaustion, paleness, difficulty concentrating, hair loss, brittle nails
Key valueFerritin - the most important lab value for assessing the iron stores
TreatmentIdentify the cause + iron supplementation (oral or intravenous)
ICD-10D50 (iron-deficiency anemia)

Table of contents

  1. What is iron deficiency?
  2. Stages: from depleted stores to anemia
  3. Symptoms
  4. Causes
  5. Diagnosis
  6. Treatment: taking iron supplements correctly
  7. Intravenous iron
  8. Diet
  9. Everyday life with iron deficiency
  10. How brite helps you
  11. FAQ
  12. Related topics

1. What is iron deficiency?

Iron is a vital trace element. The body needs it above all for forming hemoglobin - the red blood pigment that transports oxygen. Iron also plays a key role in energy metabolism, in the immune system, and in forming various enzymes.1

Iron deficiency is the most common nutritional deficiency worldwide. By estimates, a relevant share of the population is affected - especially women of childbearing age, children, older people, and people with chronic conditions.1,2

Iron deficiency ≠ iron-deficiency anemia Iron deficiency can already cause symptoms before anemia is present. Anyone who feels persistently tired and exhausted should therefore have their ferritin level checked even when hemoglobin is still in the normal range.

2. Stages: from depleted stores to anemia

Iron deficiency usually develops gradually in three stages. Symptoms can already appear in the first stage - long before hemoglobin drops.1

Stage I Storage iron depletion
Iron stores (ferritin) reduced, blood formation still adequately supplied. Often no or only mild symptoms. Lab: ferritin down, Hb still normal.
Stage II Iron-deficient erythropoiesis
The iron supply for blood formation is no longer enough. Red blood cells become smaller and paler (microcytic, hypochromic). Hb can still be normal, symptoms often increase.
Stage III Iron-deficiency anemia
Hemoglobin below the normal value. Typical anemia symptoms: marked fatigue, paleness, shortness of breath on exertion, a racing heart.

3. Symptoms

Iron-deficiency symptoms can appear before anemia and are often misinterpreted as stress, age, or being overworked.1,2

  • Fatigue and exhaustion - often the leading symptom, persists even after enough sleep
  • Difficulty concentrating, forgetfulness, reduced performance
  • Paleness - especially on the mucous membranes (eyelids, oral mucosa), palms, and nail folds
  • Hair loss - diffuse hair loss is one of the most common iron-deficiency symptoms, especially in women
  • Brittle nails, ridging, spoon nails (koilonychia) in severe cases
  • Angular cheilitis (cracked corners of the mouth)
  • Shortness of breath on exertion, a racing heart
  • Restless legs - restless legs, especially in the evening and at night
  • Sensitivity to cold
  • Susceptibility to infections - iron is important for the immune system
  • Pica - an unusual craving for non-edible substances (e.g. earth, ice, starch); rare, but typical of severe iron deficiency

4. Causes

Iron deficiency arises when the body loses or uses more iron than is taken in through food. The cause usually has to be identified - iron deficiency is often a symptom of an underlying condition.1

Increased iron loss

  • Menstrual bleeding - the most common cause in women of childbearing age; especially with heavy or long bleeding
  • Bleeding in the gastrointestinal tract - e.g. with gastritis, stomach ulcers, bowel polyps, hemorrhoidal bleeding, bowel cancer, inflammatory bowel diseases (Crohn's disease, ulcerative colitis)
  • Regular blood donation, blood draws in the chronically ill

Reduced iron absorption

  • Celiac disease - a common cause of iron deficiency that is easily overlooked
  • Inflammatory bowel diseases
  • Stomach operations, bariatric surgery
  • Long-term PPI treatment (pantoprazole, omeprazole) - can impair iron absorption
  • An iron-poor diet - especially with a vegan or very one-sided diet

Increased iron requirement

  • Pregnancy and breastfeeding
  • Growth phases in children and adolescents
  • Competitive sport
In men and in women after menopause: rule out a source of bleeding In men and in women after menopause, with iron deficiency a source of bleeding in the gastrointestinal tract should usually always be ruled out - even when there are no symptoms. Iron deficiency can be the first sign of bowel cancer.

5. Diagnosis

Diagnosing iron deficiency is usually straightforward.1

  • Ferritin: the most important lab value for assessing the iron stores. A lowered ferritin proves iron deficiency. Note: ferritin is an acute-phase protein - with concurrent inflammation, infection, or liver disease it can be falsely normal or raised, even though iron deficiency is present.
  • Complete blood count: hemoglobin, MCV (mean cell volume), MCH (mean cell hemoglobin). With iron-deficiency anemia usually: Hb down, MCV down (microcytic), MCH down (hypochromic).
  • Transferrin saturation: can help with the assessment, especially when ferritin is distorted by inflammation. With iron deficiency, usually lowered.
  • CRP: to rule out concurrent inflammation that can keep ferritin falsely normal.
  • Searching for the cause: gynecological history (menstruation?), gastroenterological workup (gastroscopy, colonoscopy if GI bleeding is suspected), celiac serology, medication history (PPIs? NSAIDs?).

More: preparing for a doctor's appointment, understanding blood test results.

6. Treatment: taking iron supplements correctly

Treatment consists of two steps: treating the cause (e.g. stopping a source of bleeding, treating celiac disease) and refilling the iron stores. The dosage is set individually by your treating practice.1

First choice Oral iron supplementation

Iron tablets or drops are usually the first choice for uncomplicated iron deficiency. Taking them does, however, require a few rules to ensure good absorption:

  • Take on an empty stomach - usually some time before breakfast, since absorption is best on an empty stomach
  • Not together with coffee, tea, milk, or calcium products - these can considerably reduce absorption
  • Vitamin C (e.g. a glass of orange juice) can improve absorption
  • Keep a gap from levothyroxine and PPIs - they should usually not be taken at the same time
  • Most common side effect: gastrointestinal intolerance (constipation, nausea, dark stool). With poor tolerability, switching the preparation or taking it with a meal can help - at the cost of absorption
  • Treatment duration usually a few months - even after hemoglobin has normalized, intake should be continued to refill the stores

More: iron supplements, medications before or after meals.

Black stool while on iron tablets is normal Dark to black stool is a harmless side effect of iron preparations and no cause for concern. But: black stool without iron intake can be a sign of bleeding in the gastrointestinal tract and should be evaluated by a doctor.

7. Intravenous iron

When oral iron preparations are not tolerated, do not work well enough, or rapid refilling is necessary, iron can be given intravenously.1

Typical indications for IV iron
• Severe intolerance of oral preparations
• Malabsorption (e.g. with celiac disease, Crohn's disease, after stomach operations)
• Chronic kidney disease
• Severe anemia where rapid refilling is necessary

Intravenous administration is usually done under medical supervision. Severe allergic reactions are rare, but possible - which is why the infusion is mostly done in the practice or an outpatient clinic.

8. Diet

With a manifest iron deficiency, diet alone is usually not enough to refill the stores. Nevertheless, an iron-rich diet is sensible to prevent a renewed deficiency.

  • Heme iron (animal sources) is usually absorbed better than non-heme iron (plant sources): meat, liver, fish
  • Plant iron sources: legumes, whole-grain products, oats, spinach (actually less than often claimed), nuts, seeds
  • Vitamin C improves the absorption of plant iron - e.g. bell peppers, citrus fruits, or broccoli with an iron-rich meal
  • Inhibit iron absorption: coffee, tea, milk, and calcium supplements - usually keep a gap from iron-rich meals
  • With a vegan diet, deliberate iron planning is particularly important; regular checks of iron values are usually recommended

9. Everyday life with iron deficiency

  • Iron supplements: take on time and regularly, even when you already feel better. The stores usually need a few months to refill fully.
  • Check-ups: ferritin and complete blood count are usually checked after a few weeks to assess the treatment success.
  • Interactions: iron can affect the absorption of other medications (e.g. levothyroxine, antibiotics, PPIs). Keep a gap. More: drug interactions.
  • Keep an eye on the cause: iron deficiency often comes back if the cause is not treated. Regular checks are important.

How brite helps you with iron deficiency

Iron in the morning on an empty stomach, then wait half an hour - no coffee, no breakfast with milk, no levothyroxine at the same moment. Iron treatment often fails not because of the preparation but because of the timing gaps. brite solves that.

  • Intake reminders - iron in the morning on an empty stomach, half an hour's gap before breakfast, no coffee at the same time: brite reminds you on time and can include the vitamin C tip too. Set up a reminder
  • Interaction check - iron plus levothyroxine? Plus PPIs? Plus antibiotics? brite shows which medications block iron absorption - and which gaps make sense. Check now
  • Health journal - document ferritin, hemoglobin, energy, and symptoms over time. That way you can see clearly whether the treatment is working - and whether the deficiency comes back after stopping. Track your progress
  • Digital medication plan - all your medications clearly laid out for your GP, gynecology, and gastroenterology. Important because the search for the cause often involves several specialists. Go to the medication plan
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FAQ: common questions about iron deficiency

The most common signs are persistent fatigue, exhaustion, difficulty concentrating, paleness, hair loss, and brittle nails. A blood test (ferritin, complete blood count) usually gives quick clarity.1
Ferritin is the most important lab value. A lowered ferritin level proves iron deficiency. Note: with concurrent inflammation, ferritin can be falsely normal - then transferrin saturation helps.1
Iron is absorbed best on an empty stomach. Coffee, tea, milk, and calcium products can considerably reduce absorption. Vitamin C (e.g. orange juice) can improve absorption.
Usually a few months - even after hemoglobin has normalized, intake should be continued for some time to fully refill the iron stores. The exact duration is set by your treating practice.
With a manifest iron deficiency, usually not. Diet alone mostly does not provide enough iron to refill the stores. An iron-rich diet is, however, sensible to prevent a renewed deficiency.
Gastrointestinal complaints (constipation, nausea, dark stool) are common side effects. Possible solutions: switching the preparation, taking it with a meal (slightly worse absorption but better tolerability), liquid preparations instead of tablets. With persistent intolerance, intravenous iron can be considered.
Yes - dark to black stool is a harmless side effect of iron preparations and no cause for concern. Important: black stool without iron intake can be a sign of bleeding in the gastrointestinal tract and should be evaluated by a doctor.
When oral preparations are not tolerated, with malabsorption (e.g. celiac disease, Crohn's disease), with chronic kidney disease, or with severe anemia requiring rapid refilling. The decision is made by your treating practice.1
Iron supplements Hypothyroidism (Hashimoto's) Crohn's disease Ulcerative colitis Medications before or after meals Drug interactions

Sources

  1. Onkopedia Guideline Iron Deficiency and Iron-Deficiency Anemia (DGHO, as of April 2025), Germany. onkopedia.com
  2. gesundheitsinformation.de (IQWiG): Iron-Deficiency Anemia. gesundheitsinformation.de
  3. S1 Guideline Iron-Deficiency Anemia (AWMF reg. no. 025-021), Germany. awmf.org
  4. German Society for Hematology and Medical Oncology (DGHO). dgho.de
Medical disclaimer: This article is for general information and does not replace medical advice, diagnosis, or treatment. With iron deficiency, the cause should usually be evaluated by a doctor - especially in men and in women after menopause (ruling out a source of bleeding). Dosing and the choice of preparation are always set individually by your treating practice. Last updated: April 2026.