What is the most common cause of low red blood cell count?

September 25, 2025 •

4 min read

Globally, iron deficiency is the most prevalent cause of anemia, the condition defined by a low red blood cell (RBC) count. Understanding what is the most common cause of low red blood cell count is the first step toward effective diagnosis and treatment.

Quick Summary

The most frequent cause of low red blood cell count is iron deficiency anemia, which often stems from inadequate dietary intake or chronic blood loss. Underlying health conditions, nutritional deficiencies, and other factors can also contribute to the decrease in red blood cells.

Key Points

Iron Deficiency: Iron deficiency is the most common cause of anemia, often resulting from insufficient dietary iron or chronic blood loss, such as heavy menstruation or gastrointestinal issues.
Blood Loss: Both acute (sudden) and chronic (long-term) blood loss can deplete the body's iron stores, directly leading to a lower red blood cell count.
Vitamin Deficiencies: A lack of vitamin B12 or folate can impair red blood cell production, causing megaloblastic anemia where cells are abnormally large.
Chronic Illness: Persistent inflammation from conditions like kidney disease, cancer, or autoimmune disorders can suppress red blood cell production in the bone marrow.
Diagnosis is Key: Proper diagnosis through blood tests like a Complete Blood Count (CBC) is essential to determine the specific cause of a low red blood cell count and guide treatment.
Dietary Role: Your diet plays a major role in preventing certain types of anemia, with adequate intake of iron, B12, and folate being critical for healthy red blood cell production.

Understanding Anemia and Red Blood Cells

Red blood cells, also known as erythrocytes, are essential for transporting oxygen throughout the body. They contain a protein called hemoglobin, which binds to oxygen and gives blood its characteristic red color. A low red blood cell count, also known as anemia, means your body's tissues and organs are not receiving enough oxygen, leading to symptoms like fatigue, weakness, and shortness of breath. While many conditions can cause a low red blood cell count, one cause is seen far more frequently than others.

Iron Deficiency: The Leading Cause

Iron deficiency anemia is the most common type of anemia worldwide. Your bone marrow needs iron to produce hemoglobin for red blood cells. Without sufficient iron, the body cannot create enough healthy red blood cells, which results in a low count.

Factors contributing to iron deficiency include:

Blood Loss: Chronic or acute blood loss is a primary driver. This can be caused by heavy menstrual periods, internal bleeding from gastrointestinal ulcers, colon polyps, or certain cancers. Regular use of NSAIDs like aspirin can also lead to slow internal bleeding.
Dietary Factors: A diet lacking sufficient iron, particularly common in infants, young children, vegans, and vegetarians, can lead to iron deficiency.
Poor Iron Absorption: Certain intestinal conditions like celiac disease or Crohn's disease, or surgeries such as gastric bypass, can inhibit the body's ability to absorb iron from food.
Pregnancy: The increased blood volume and iron requirements to support a developing fetus make iron deficiency anemia common during pregnancy if not managed with supplements.

Other Nutritional Deficiencies

Beyond iron, other nutrients are vital for red blood cell production. Deficiencies in these can also cause anemia.

Vitamin B12 Deficiency: Vitamin B12 is crucial for the formation of red blood cells. A lack of B12 can result in megaloblastic anemia, where red blood cells are abnormally large and oval-shaped. This can be due to a poor diet or, more commonly, an autoimmune condition called pernicious anemia, which prevents the absorption of B12.
Folate (B9) Deficiency: Like B12, folate is necessary for proper red blood cell development. Low folate can also lead to megaloblastic anemia and may result from a poor diet or malabsorption.

Anemia of Chronic Disease

This type of anemia is linked to persistent inflammatory conditions. Chronic inflammation can interfere with the production of red blood cells by affecting the bone marrow. Conditions commonly associated with this include:

Cancer
HIV/AIDS
Rheumatoid arthritis
Kidney disease
Inflammatory bowel diseases like Crohn's disease

Problems with the Bone Marrow

Since the bone marrow is where red blood cells are produced, issues with this spongy tissue can significantly impact their count.

Aplastic Anemia: This rare and serious condition occurs when the bone marrow stops producing new blood cells. It can be triggered by infections, autoimmune diseases, or exposure to toxic chemicals.
Bone Marrow Disorders: Diseases such as leukemia and myelofibrosis can affect how the bone marrow makes blood, from mild to life-threatening effects.

Hemolytic Anemias

This group of anemias involves the premature destruction of red blood cells, which the bone marrow cannot replace quickly enough. Hemolytic anemias can be inherited or acquired through infections or autoimmune disorders.

Sickle Cell Anemia: An inherited condition where hemoglobin is abnormal, forcing red blood cells into a sickle shape that die prematurely.
Thalassemia: An inherited disorder where the body produces an abnormal form of hemoglobin.

Comparing Common Causes of Low Red Blood Cell Count


Cause	Mechanism	Key Indicators	At-Risk Populations
Iron Deficiency	Insufficient iron for hemoglobin production	Small, pale red blood cells (microcytic anemia), low ferritin levels	Menstruating/pregnant women, vegetarians, individuals with chronic blood loss
Vitamin B12 Deficiency	Impaired production of healthy red blood cells due to lack of B12	Abnormally large red blood cells (megaloblastic anemia)	Older adults, vegans, individuals with malabsorption issues (pernicious anemia)
Chronic Disease	Persistent inflammation suppresses red blood cell production in bone marrow	Often mild to moderate anemia, normal-sized red blood cells (normocytic)	People with cancer, kidney disease, autoimmune disorders
Chronic Blood Loss	Gradual loss of red blood cells depletes iron stores over time	Similar to iron deficiency; possible GI symptoms	Menstruating women, individuals with ulcers, GI bleeding
Hemolytic Anemia	Rapid destruction of red blood cells, faster than bone marrow production	Low RBC count with signs of high RBC turnover	Individuals with inherited conditions, autoimmune diseases, or infections

Diagnosis and Management

Diagnosing the cause of a low red blood cell count requires a comprehensive approach by a healthcare provider. A key diagnostic tool is the complete blood count (CBC), which measures red blood cells, hemoglobin, and hematocrit. Further testing, such as iron studies, vitamin B12 levels, or a bone marrow biopsy, may be necessary to pinpoint the specific cause. Treatment is tailored to the root cause and can involve dietary adjustments, supplements, medication, or managing the underlying chronic condition. For inherited anemias or severe cases, more advanced treatments like blood transfusions or bone marrow transplants may be needed.

Conclusion

While many factors can lead to a low red blood cell count, iron deficiency stands out as the most common cause globally, often linked to blood loss or poor diet. However, chronic diseases, other nutritional deficiencies, and genetic disorders can also play a role. A proper diagnosis from a healthcare professional is crucial for determining the specific type of anemia and establishing an effective treatment plan to restore optimal health and energy. For more detailed information on anemia and blood health, consulting an authoritative resource like the National Heart, Lung, and Blood Institute is recommended.

Frequently Asked Questions

Symptoms can include fatigue, weakness, pale skin, headaches, dizziness, and shortness of breath. Symptoms may be mild at first and worsen as the condition progresses.

While a balanced diet rich in iron, vitamin B12, and folate can help prevent and treat nutritional anemias, it may not be sufficient if the underlying cause is chronic blood loss, a medical condition, or a malabsorption issue. Always consult a healthcare provider.

A doctor can diagnose iron-deficiency anemia with a Complete Blood Count (CBC) and specific iron tests that measure ferritin, serum iron, and total iron-binding capacity. The CBC often shows small, pale red blood cells.

Yes, a low red blood cell count, or low hemoglobin, is the defining characteristic of anemia. However, anemia itself can be a sign of many different underlying issues, from nutritional deficiencies to chronic diseases.

Yes, heavy menstrual bleeding is a common cause of chronic blood loss, which can lead to iron deficiency anemia over time as the body loses iron faster than it can be replaced.

Hemolytic anemia occurs when red blood cells are destroyed faster than the bone marrow can produce new ones. This can be due to inherited conditions, autoimmune diseases, or infections.

If you experience symptoms like persistent fatigue, pale skin, dizziness, or shortness of breath, you should see a doctor. A simple blood test can determine your red blood cell count and help identify the cause.