The main causes of anemia

Anemia happens when your body either doesn't make enough red blood cells, destroys them too quickly, or loses them faster than it can replace them. The reason this happens depends on what's going wrong inside your body — and there are dozens of different causes. Some are straightforward to fix, like a missing nutrient. Others are more complex, like a chronic disease or a genetic condition you were born with.

The three broad categories are: your bone marrow isn't producing enough cells, your body is destroying cells faster than normal, or you're losing blood. Most people fall into one of these groups, and understanding which one applies to you helps explain what happens next in your care.

Key Takeaways

  • Iron, vitamin B12, and folate deficiencies are the most common causes of anemia and are often reversible with supplements or dietary changes.
  • Chronic diseases like kidney disease, heart disease, and cancer can lower the hormones or conditions your body needs to make red blood cells.
  • Some people are born with genetic conditions like sickle cell disease or thalassemia that affect how their red blood cells form or function.
  • Blood loss from heavy periods, ulcers, or other internal bleeding can deplete your red blood cells faster than your body replaces them.
  • Certain medications and autoimmune conditions can cause your immune system to attack and destroy your own red blood cells.

Nutritional deficiencies that lead to anemia

Your bone marrow needs specific nutrients to build red blood cells. When you don't get enough of them, production slows down. The three most common deficiencies are iron, vitamin B12, and folate.

Iron deficiency is the most frequent cause of anemia worldwide. Your body uses iron to make hemoglobin, the protein inside red blood cells that carries oxygen. Without enough iron, you can't make hemoglobin, so your cells come out smaller and paler. This happens when you don't eat enough iron-rich foods, your body can't absorb iron properly, or you're losing blood regularly — like through heavy menstrual periods or a bleeding ulcer.

Vitamin B12 deficiency occurs when you don't eat enough animal products, your stomach can't absorb B12 properly, or you've had surgery that removes part of your digestive tract. B12 is essential for your bone marrow to make healthy red blood cells. Without it, the cells that do form are often larger than normal and don't work as well.

Folate deficiency develops similarly — your body needs folate (a B vitamin) to divide cells and make DNA. Pregnancy, certain medications, and some digestive disorders can deplete your folate stores. Alcoholism also interferes with folate absorption and storage.

Chronic diseases that cause anemia

Long-term illnesses can trigger anemia even when you're eating well and your blood isn't visibly leaking. These conditions affect the hormones or environment your bone marrow needs to work properly.

Kidney disease is one of the most common culprits. Your kidneys produce erythropoietin (EPO), a hormone that tells your bone marrow to make more red blood cells. When your kidneys are damaged, they produce less EPO, so your marrow slows production. This happens in both early and advanced kidney disease.

Cancer and cancer treatment can cause anemia in multiple ways. The cancer itself may damage your bone marrow, chemotherapy drugs can kill bone marrow cells along with cancer cells, or the cancer may cause chronic bleeding. Some cancers also trigger your immune system to attack your own red blood cells.

Other chronic conditions that frequently lead to anemia include heart disease, diabetes, rheumatoid arthritis, lupus, inflammatory bowel disease, and HIV. These conditions create ongoing inflammation in your body, which interferes with red blood cell production or causes your immune system to destroy cells faster.

Genetic and inherited blood disorders

Some people are born with conditions that affect how their red blood cells form or function. These are inherited from parents and present from birth, though symptoms may not appear until later in childhood or adulthood.

Sickle cell disease causes red blood cells to become crescent-shaped instead of round. These rigid cells get stuck in blood vessels, blocking blood flow and breaking apart faster than normal cells. This leads to hemolytic anemia — anemia caused by cells being destroyed too quickly.

Thalassemia is a genetic disorder where your body makes abnormal hemoglobin. Depending on the type, your red blood cells may be destroyed quickly or your bone marrow may not produce enough cells. Thalassemia ranges from mild to severe.

Hereditary spherocytosis and other inherited conditions affect the shape or structure of red blood cells, making them fragile and prone to breaking down in your spleen. These are less common than sickle cell or thalassemia but follow the same pattern: cells are destroyed faster than your body can replace them.

Blood loss and bleeding disorders

When you lose blood faster than your bone marrow can make new red blood cells, anemia develops. This can happen suddenly from a major injury or slowly from ongoing bleeding you might not notice.

Heavy menstrual bleeding is one of the most common causes of anemia in women of childbearing age. If your periods last longer than seven days or you soak through one or more pads or tampons every hour for several hours, you're losing more blood than normal. Over months, this depletes your iron stores.

Gastrointestinal bleeding from ulcers, inflammatory bowel disease, hemorrhoids, or polyps can cause slow, steady blood loss that you don't see. You might notice dark or tarry stools, which indicate blood in your digestive tract. Serious bleeding can happen suddenly, but chronic low-level bleeding is more common.

Other sources of blood loss include nosebleeds, bleeding gums, urinary tract bleeding, and injuries. People with bleeding disorders like hemophilia or von Willebrand disease have trouble clotting, so even minor cuts or internal bleeding can lead to significant blood loss over time.

Autoimmune and medication-related causes

Sometimes your immune system mistakenly attacks your own red blood cells, destroying them faster than your bone marrow can replace them. This is called autoimmune hemolytic anemia. It can develop on its own or alongside other autoimmune conditions like lupus or rheumatoid arthritis.

Certain medications can also trigger anemia. Some drugs directly damage bone marrow cells and reduce production. Others cause your immune system to attack red blood cells. Medications that commonly cause anemia include some antibiotics, anti-seizure drugs, and immunosuppressants. If you develop anemia after starting a new medication, your doctor may switch you to an alternative.

Infections can also cause hemolytic anemia — your immune system may attack red blood cells while fighting off bacteria or viruses. This is usually temporary and resolves once the infection clears.

Bone marrow disorders

Your bone marrow is the factory where red blood cells are made. When the marrow itself is damaged or diseased, it can't produce enough cells, even if you have all the nutrients you need.

Aplastic anemia occurs when your bone marrow stops producing adequate numbers of red blood cells, white blood cells, and platelets. This can be triggered by certain medications, infections, autoimmune disease, or radiation. Sometimes no clear cause is found.

Myelodysplastic syndromes are disorders where bone marrow produces cells that are abnormal or don't function properly. These are more common as people age and can progress to leukemia over time.

Leukemia and lymphoma are cancers of blood cells that crowd out normal red blood cell production in the bone marrow. As cancer cells multiply, there's less room for healthy cells to form.

Frequently Asked Questions

Can anemia be caused by not eating enough?

Yes, if your diet lacks iron, vitamin B12, or folate. Vegetarians and vegans are at higher risk for B12 deficiency since it comes mainly from animal products. People who eat very little meat or dairy may develop iron deficiency. A doctor can test your nutrient levels to confirm.

Is anemia always serious?

Not always. Mild iron deficiency anemia from heavy periods or a poor diet is common and often reversible with supplements or dietary changes. Severe anemia or anemia from serious conditions like cancer or bone marrow disease is more concerning and requires treatment. Your doctor will determine how serious yours is based on your blood counts and symptoms.

Can you develop anemia suddenly or does it take time?

Both happen. Anemia from sudden blood loss (like a car accident) develops within hours. Anemia from nutritional deficiency or chronic disease develops slowly over weeks or months, which is why you might not notice symptoms at first. Your doctor can tell how long you've had anemia by looking at your blood cell sizes and iron stores.

Does anemia run in families?

Some types do. Sickle cell disease, thalassemia, and hereditary spherocytosis are inherited genetic conditions. If your parents or siblings have these conditions, your risk is higher. Other causes like nutritional deficiency or kidney disease are not inherited, though family members might share similar diets or health conditions.

Can medications cause anemia?

Yes. Some medications damage bone marrow or trigger your immune system to attack red blood cells. If anemia develops after you start a new medication, tell your doctor — they may switch you to a different drug or adjust your dose. Never stop taking a medication without talking to your doctor first.