Vitamin B12 deficiency anemia refers to a condition where the body does not have a sufficient amount of healthy red blood cells due to a lack of vitamin B12. Without enough B12, the body may not be able to produce enough red blood cells to supply the body with oxygen comfortably.

Vitamin B12, or cobalamin, is an important B vitamin that plays a crucial role in a number of bodily functions, including the production of red blood cells (RBCs). As a lack of vitamin B12 may decrease the number of healthy circulating RBCs, a person without enough B12 may experience anemia. This can occur due to malabsorption, an underlying condition, or diet. Treatment typically involves supplementation of vitamin B12.

In this article, we will discuss B12 deficiency anemia, including the different types, causes, and treatments.

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Vitamin B12 is a water-soluble vitamin that contains the mineral cobalt and is sometimes known as cobalamin. It is present in foods such as fish, meat, and dairy products. The body uses vitamin B12 for:

  • creating new RBCs
  • DNA synthesis
  • brain and neurological function
  • fat and protein metabolism

The recommended dietary allowance for vitamin B12 may vary among individuals due to different factors, but it is roughly 2.4 micrograms for most adults.

Vitamin B12 deficiency anemia occurs when a person’s levels of B12 are too low, meaning the body is not able to produce enough healthy RBCs. When this happens, the body may not produce enough RBCs to supply the body with oxygen adequately. Without enough oxygen, the body cannot work as well, causing a person to experience fatigue, weakness, and other complications.

Vitamin B12 deficiency anemia is a type of megaloblastic anemia. This term describes when RBCs do not develop normally. Instead, they are very large and have a more oval shape than healthy, mature RBCs. Deficiency in another B vitamin, known as folate, is another type of megaloblastic anemia.

Some common causes of vitamin B12 deficiency anemia include:

Autoimmune conditions

Pernicious anemia is an autoimmune condition that affects the lining of the stomach and prevents the production of a protein called intrinsic factor. This is due to the immune system creating antibodies that attack the parietal cells, which line the stomach and produce this protein. Intrinsic factor helps the body absorb vitamin B12 in the small intestine. When a person lacks this protein, they can become deficient in vitamin B12.

Pernicious anemia is often associated with other autoimmune conditions such as type 1 diabetes, vitiligo, and thyroid conditions. Pernicious anemia is a rare condition, but evidence suggests it is more common in people of Northern European descent and over the age of 60.

Intestinal conditions

Chronic inflammation of the stomach lining, or chronic gastritis, can prevent the secretion of intrinsic factor and stomach acids, which play a key role in helping the body absorb vitamin B12.

Inflammation may be due to autoimmune conditions, such as Crohn’s disease and celiac disease. Alternatively, it may occur due to infections such as Helicobacter pylori.


Some surgeries, such as gastric bypass or small bowel resection, may involve rearranging or removing parts of the gastrointestinal tract. As a result of these anatomical changes, a person may experience difficulties absorpting vitamin B12.

Evidence suggests that vitamin B12 deficiency is common after this type of surgery, with 13–60% of people experiencing a deficiency.


Long-term use of certain medications may also prevent the body from absorbing vitamin B12 and lead to a deficiency. Some medications associated with poor vitamin B12 absorption include:


Vitamin B12 is only present in animal-based foods. People who have diets low in these foods, such as vegan and vegetarian diets, may not consume enough vitamin B12 and become deficient.

Risk factors

Some factors that may make a person more at risk of vitamin B12 deficiency anemia include:

  • having a family member with the condition
  • having an autoimmune condition associated with the deficiency, including thyroid disease, diabetes, and vitiligo
  • older age, as the risk of B12 malabsorption increases with age

Symptoms of vitamin B12 deficiency anemia can develop slowly and may vary from person to person. Symptoms may include:

Click here to learn more about the symptoms of vitamin B12 deficiency.

While complications are rare, people with severe anemia are at a higher risk of developing heart and lung complications due to difficulties supplying the vital organs with oxygen. Additionally, people with vitamin B12 deficiency anemia may also experience:

Vitamin B12 deficiency anemia can be difficult for a doctor to diagnose due to its broad symptoms and frequent association with other conditions. Often, a doctor may diagnose the condition during a medical exam through a routine blood test.

To diagnose vitamin B12 deficiency anemia, a doctor may ask a person about their medical history, perform a physical exam, and run some blood tests. This includes a complete blood count, which will pick up any abnormalities in RBCs and amount of hemoglobin, as well as a person’s serum vitamin B12 levels.

If the blood test shows signs of anemia, further tests may be necessary to find the cause. Such tests may include:

  • a blood test to see a person’s reticulocyte count and measure the number of young RBCs
  • a blood test for intrinsic factor antibodies associated with pernicious anemia
  • bone marrow tests to see if a person’s bone marrow is making RBCs properly

Treatment typically involves supplementing vitamin B12 to bring a person’s levels back into a healthy range. The duration and form of treatment can vary depending on the cause of a person’s B12 deficiency.

For people who are deficient due to dietary causes, a doctor may prescribe oral B12 supplements to relieve symptoms. A person may also work with a dietitian to try and include more vitamin B12 into their diet. Foods high in vitamin B12 include:

  • fish
  • meat
  • poultry
  • eggs
  • dairy products

If a person wishes to include vitamin B12 into their diet without consuming animal products, they can consume foods fortified with vitamin B12, such as yeast extracts, cereals, and some plant milks.

Click here to learn more about the best foods for vitamin B12.

In the case of malabsorption, treatment often involves a doctor administering an injection of B12. Injecting the vitamin into a muscle allows the body to absorb the vitamin without involving the digestive system. Examples of these injections include cyanocobalamin or hydroxocobalamin.

At the beginning of treatment, a person may receive these injections frequently to replenish their stores before moving to monthly injections. For some people, this treatment may need to be lifelong to keep their vitamin B12 levels in a healthy range.

Symptoms of B12 deficiency anemia can resemble several other conditions, and long-term deficiency can cause symptoms to become more severe. A person experiencing any symptoms may wish to contact a doctor to understand the cause of their symptoms and promptly start treatment.

Vitamin B12 deficiency anemia describes when a lack of vitamin B12 affects the production of healthy red blood cells. Due to a lower number of healthy red blood cells, people may experience symptoms of anemia, such as weakness, fatigue, and shortness of breath.

The condition can occur due to other underlying medical conditions, certain medications, or following surgery. To help manage a deficiency, a doctor may suggest using B12 supplements and adding B12-rich or fortified foods to the diet.