Learn About Common Causes of Anemia

What Is Anemia and How Does It Develop?

Anemia is a condition in which your blood does not have enough healthy red blood cells to carry oxygen throughout your body. Red blood cells contain a protein called hemoglobin, which binds to oxygen in your lungs and delivers it to tissues and organs. When you have anemia, your blood carries less oxygen than normal, which can leave you feeling tired, weak, or short of breath.

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Your body produces millions of red blood cells every day in the bone marrow—the soft tissue inside larger bones. These cells typically live about 120 days before your body breaks them down and removes them. Anemia develops when one of three things happens: your body does not make enough red blood cells, your body destroys red blood cells faster than it can replace them, or you lose blood faster than your body can make new red blood cells.

The severity of anemia varies widely. Some people have mild anemia with few noticeable symptoms, while others experience significant symptoms that affect daily activities. Anemia is quite common: according to the World Health Organization, approximately 1.62 billion people worldwide have anemia. In the United States, about 3 million people have iron-deficiency anemia, which is the most common type.

Understanding how anemia develops helps explain why different people experience different symptoms and why different treatments work for different types of anemia. The underlying cause of your anemia determines which treatment approaches may help and how your condition might progress.

Practical Takeaway: Anemia occurs when your blood cannot carry enough oxygen because of low red blood cell numbers or hemoglobin levels. Recognizing this basic mechanism helps you understand why your doctor may recommend specific tests or treatments based on your individual situation.

Iron-Deficiency Anemia: The Most Common Type

Iron-deficiency anemia occurs when your body does not have enough iron to make hemoglobin. Iron is a mineral your body uses to create hemoglobin, the protein that allows red blood cells to transport oxygen. Without adequate iron, your body cannot make sufficient hemoglobin, which leads to fewer functional red blood cells.

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Iron-deficiency anemia accounts for roughly 50 percent of all anemia cases worldwide and is the leading cause of anemia globally. In the United States, it affects approximately 7-10 percent of children and 9-12 percent of women of reproductive age. The condition develops over time as your body's iron stores become depleted.

Several situations increase your risk of developing iron-deficiency anemia. Heavy menstrual bleeding is a leading cause in women of reproductive age—if you lose more than 80 milliliters of blood during your period, you may struggle to maintain adequate iron levels. Pregnancy increases iron needs significantly because you must produce extra blood to support both yourself and a developing baby. Gastrointestinal bleeding from ulcers, inflammatory bowel disease, or polyps can cause chronic blood loss that depletes iron stores. Poor dietary intake of iron-rich foods, particularly in vegetarians or vegans who do not consume animal sources of iron, may contribute to developing this type of anemia. Certain medical conditions that affect how your body absorbs nutrients, such as celiac disease or Crohn's disease, can prevent you from absorbing dietary iron effectively.

You might experience specific symptoms with iron-deficiency anemia, including extreme fatigue, weakness, pale or yellowish skin, shortness of breath with minimal exertion, dizziness or lightheadedness, cold hands and feet, or brittle nails. Some people develop an unusual craving for non-food items like ice, dirt, or starch—a condition called pica.

Practical Takeaway: Iron-deficiency anemia is the most common type and develops when your body lacks sufficient iron to produce hemoglobin. Identifying whether you have risk factors like heavy periods, pregnancy, or gastrointestinal bleeding can help you understand your condition and discuss appropriate monitoring with your healthcare provider.

Vitamin B12 and Folate Deficiency Anemia

Your body needs both vitamin B12 and folate (vitamin B9) to produce healthy red blood cells. These vitamins help your bone marrow create red blood cells with normal size and shape. When you lack sufficient B12 or folate, your bone marrow produces fewer red blood cells, and the cells that do form are often larger than normal—a condition called megaloblastic anemia. Both B12 and folate deficiency can occur separately or together, and both require different approaches to address.

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Vitamin B12 deficiency can develop for several reasons. Your body obtains B12 exclusively from animal-based foods like meat, fish, eggs, and dairy products, so strict vegans who do not consume these foods may develop deficiency over time. Your stomach produces a protein called intrinsic factor that allows your intestines to absorb B12 from food. Pernicious anemia occurs when your immune system attacks cells in your stomach that produce intrinsic factor, preventing B12 absorption. This autoimmune condition becomes more common with age and affects roughly 1-2 percent of people over age 60. Gastrointestinal surgery, inflammatory bowel disease, or celiac disease can reduce your ability to absorb B12. Certain medications like metformin (used for diabetes) and proton pump inhibitors (used for acid reflux) can interfere with B12 absorption if used long-term.

Folate deficiency typically develops from inadequate dietary intake. Your body does not store large amounts of folate, so you need a continuous dietary supply. Leafy green vegetables, legumes, asparagus, and fortified grains all contain folate. Pregnant women need significantly more folate to prevent birth defects—the recommendation increases from 400 micrograms daily to 600 micrograms during pregnancy. Excessive alcohol consumption increases folate deficiency risk because alcohol interferes with folate absorption and storage. Certain medications like methotrexate (used for cancer and autoimmune conditions) can deplete folate levels.

Symptoms of B12 or folate deficiency anemia include fatigue, weakness, pale skin, shortness of breath, numbness or tingling in hands and feet (particularly with B12 deficiency), confusion or memory problems, difficulty concentrating, and mood changes including depression or irritability. B12 deficiency can also cause a sore or swollen tongue and a distinctive bright red color to the tongue.

Practical Takeaway: B12 and folate deficiency anemia can develop from dietary insufficiency, absorption problems, or certain medications. Understanding your dietary patterns and whether you have conditions affecting nutrient absorption can help inform conversations with your healthcare provider about monitoring or supplementation.

Anemia of Chronic Disease and Hemolytic Anemia

Anemia of chronic disease occurs when you have a long-term health condition that interferes with your body's ability to produce red blood cells or causes them to break down faster than normal. This type of anemia frequently develops in people with kidney disease, cancer, rheumatoid arthritis, lupus, inflammatory bowel disease, heart disease, or chronic infections like HIV or tuberculosis. Anemia of chronic disease is the second most common type of anemia after iron-deficiency anemia and affects millions of people with ongoing health conditions.

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When you have a chronic disease, your body produces increased amounts of a hormone called hepcidin. Hepcidin regulates iron absorption and storage, and elevated levels prevent your intestines from absorbing dietary iron effectively. Additionally, chronic inflammation reduces production of a hormone called erythropoietin, which signals your bone marrow to produce red blood cells. The combination of reduced red blood cell production and impaired iron availability leads to anemia. Treating anemia of chronic disease requires managing the underlying chronic condition, as the anemia typically improves when the primary disease is controlled.

Hemolytic anemia differs from other types because your body destroys red blood cells faster than it produces them. While normal red blood cells live about 120 days, hemolytic anemia causes cells to break down in days or weeks. Your bone marrow attempts to compensate by producing extra cells, but it cannot keep pace with the destruction rate. Hemolytic anemia may be inherited or acquired. Inherited forms include sickle cell disease, where abnormal hemoglobin causes red blood cells to become rigid and curved, and hereditary spherocytosis, where red blood cells have an abnormal shape. Acquired hemolytic anemia can result from auto