The most common causes of anemia
Anemia happens when your body doesn't have enough red blood cells or hemoglobin—the protein that carries oxygen through your blood. The reason varies widely. Iron deficiency is the most common cause worldwide, followed by chronic disease, vitamin deficiencies, and blood loss. Some people are born with conditions that affect how their body makes or uses red blood cells. Others develop anemia because of medications, kidney problems, or cancer treatment.
The cause matters because it determines what happens next—what your doctor will test for, what treatment might work, and whether the anemia will resolve on its own or needs ongoing management. Understanding what's behind your anemia is the first step toward addressing it.
Key Takeaways
- Iron deficiency anemia develops when your body lacks enough iron to make hemoglobin, usually from blood loss, poor diet, or absorption problems.
- Vitamin B12 and folate deficiencies prevent your body from making healthy red blood cells, even if iron levels are normal.
- Chronic diseases like kidney disease, heart disease, and cancer can trigger anemia by reducing how much of a hormone called erythropoietin your body produces.
- Some people inherit genes that cause their red blood cells to be shaped wrong or break down too quickly, such as sickle cell disease or thalassemia.
- Medications, autoimmune conditions, and bone marrow disorders can all interfere with red blood cell production or survival.
Iron deficiency: the most common type
Iron deficiency anemia develops when your body doesn't have enough iron to build hemoglobin. Iron is the core of the hemoglobin molecule—without it, your red blood cells can't carry oxygen effectively. This is the most common form of anemia in the world, especially in women of childbearing age and in countries where malnutrition is widespread.
Iron deficiency usually comes from one of three sources: blood loss, poor intake, or absorption problems. Chronic blood loss—from heavy periods, bleeding ulcers, or colorectal polyps—is the leading cause in developed countries. Poor diet, especially one low in red meat, poultry, beans, and fortified grains, can deplete iron over time. Absorption problems occur when your digestive system can't pull iron from food properly, which happens with celiac disease, Crohn's disease, or after gastric bypass surgery.
Your doctor will measure ferritin and serum iron levels to confirm iron deficiency. Treatment usually involves iron supplements by mouth or, less commonly, iron infusions if absorption is severely impaired.
Vitamin B12 and folate deficiencies
Your bone marrow needs both B12 and folate to manufacture red blood cells. Without enough of either vitamin, your body produces fewer cells, and the ones it does make are often larger and less functional. Pernicious anemia, the most common B12-related form, happens when your stomach can't absorb B12 from food because it lacks a protein called intrinsic factor—usually because of an autoimmune condition.
B12 deficiency also occurs in strict vegetarians and vegans who don't eat animal products, in people with digestive disorders that affect absorption, and in those taking metformin or proton pump inhibitors long-term. Folate deficiency is less common in developed countries because many foods are fortified, but it can develop from poor diet, pregnancy, dialysis, or certain medications like methotrexate.
Testing involves measuring B12 and folate levels in your blood. B12 deficiency is treated with injections or high-dose oral supplements; folate deficiency usually responds to oral folate pills or dietary changes.
Chronic disease and kidney problems
Long-standing illness can trigger anemia even when iron and vitamins are adequate. Chronic kidney disease is the most common culprit: your kidneys produce a hormone called erythropoietin (EPO) that tells your bone marrow to make red blood cells. When kidney function declines, EPO production drops, and red blood cell production slows.
Other chronic conditions that cause anemia include heart disease, diabetes, rheumatoid arthritis, lupus, inflammatory bowel disease, and cancer. These conditions often trigger inflammation, which interferes with iron absorption and EPO signaling. Cancer patients also become anemic from chemotherapy and radiation, which damage bone marrow directly.
Treating anemia from chronic disease means managing the underlying condition and sometimes using EPO-stimulating medications or blood transfusions if the anemia is severe.
Inherited blood disorders
Some people inherit genes that affect how their red blood cells are made or how long they survive. Sickle cell disease causes red blood cells to become crescent-shaped and rigid, so they get stuck in blood vessels and break down faster than normal cells. Thalassemia is a group of inherited disorders where the genes that code for hemoglobin are faulty, resulting in abnormal or insufficient hemoglobin production.
Both conditions are inherited in an autosomal recessive pattern, meaning you need to inherit the faulty gene from both parents to have the disease. People who inherit the gene from only one parent are carriers and usually have no symptoms, though they may have mild anemia.
Other inherited disorders include hereditary spherocytosis, where red blood cells are shaped abnormally and break down too quickly, and glucose-6-phosphate dehydrogenase (G6PD) deficiency, which makes red blood cells fragile when exposed to certain medications or foods.
Autoimmune and bone marrow disorders
Autoimmune hemolytic anemia occurs when your immune system mistakenly attacks and destroys your own red blood cells. Your bone marrow tries to replace them, but can't keep up with the destruction. This can happen on its own or as part of another autoimmune disease like lupus or rheumatoid arthritis.
Bone marrow disorders directly interfere with red blood cell production. Aplastic anemia happens when bone marrow stops producing enough blood cells of all types. Myelodysplastic syndromes are a group of disorders where bone marrow produces abnormal cells that don't function properly. Leukemia and lymphoma can crowd out normal blood cell production.
These conditions are diagnosed through blood tests and sometimes bone marrow biopsy. Treatment varies widely depending on the specific disorder and its severity.
Medications and other triggers
Some medications can cause or worsen anemia. Chemotherapy drugs damage bone marrow. Antibiotics like sulfonamides and nitrofurantoin can trigger hemolytic anemia in people with G6PD deficiency. Methotrexate, used for cancer and autoimmune diseases, interferes with folate metabolism. ACE inhibitors and some other blood pressure medications can reduce EPO production.
Alcohol use disorder damages bone marrow and interferes with folate absorption. Severe infections, especially sepsis, can destroy red blood cells faster than bone marrow can replace them. Pregnancy increases demand for iron and folate, sometimes unmasking a deficiency that wasn't apparent before.
If you develop anemia after starting a new medication, tell your doctor. Sometimes switching to a different drug resolves the problem.
Frequently Asked Questions
Can anemia go away on its own?
It depends on the cause. Iron deficiency anemia from a one-time blood loss may resolve if you eat iron-rich foods and your body replaces the lost iron. Anemia from vitamin deficiency usually improves once you correct the deficiency. Anemia from chronic kidney disease, inherited disorders, or autoimmune conditions typically requires ongoing treatment.
Is anemia always serious?
Mild anemia often causes no symptoms and may not need treatment beyond addressing the underlying cause. Severe anemia can be life-threatening because your organs aren't getting enough oxygen. The seriousness depends on how low your hemoglobin is, how quickly it dropped, and your overall health.
Can you have more than one cause of anemia at the same time?
Yes. Someone with chronic kidney disease might also have iron deficiency from blood loss. A person with B12 deficiency might also have folate deficiency. Your doctor tests for multiple causes when the obvious one doesn't fully explain your anemia.
What tests show what's causing anemia?
A complete blood count (CBC) shows how low your hemoglobin is and the size and shape of your red blood cells. Iron studies measure ferritin and serum iron. B12 and folate levels are measured separately. If those are normal, your doctor may order tests for kidney function, reticulocyte count, or bone marrow biopsy depending on what the initial results suggest.