What is the definition of Vitamin B12 Deficiency Anemia?

Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. There are many types of anemia.

Vitamin B12 deficiency anemia is a low red blood cell count due to a lack (deficiency) of vitamin B12.

What are the alternative names for Vitamin B12 Deficiency Anemia?

Megaloblastic macrocytic anemia

What are the causes for Vitamin B12 Deficiency Anemia?

Your body needs vitamin B12 to make red blood cells. In order to provide vitamin B12 to your cells:

  • You must eat foods that contain vitamin B12, such as meat, poultry, shellfish, eggs, fortified breakfast cereals, and dairy products.
  • Your body must absorb enough vitamin B12. A special protein, called intrinsic factor, helps your body do this. This protein is released by cells in the stomach.

A lack of vitamin B12 may be due to dietary factors, including:

  • Eating a strict vegetarian diet
  • Poor diet in infants
  • Poor nutrition during pregnancy

Certain health conditions can make it difficult for your body to absorb enough vitamin B12. They include:

  • Alcohol use 
  • Crohn disease, celiac disease, infection with the fish tapeworm, or other problems that make it difficult for your body to digest foods
  • Pernicious anemia, a type of vitamin B12 anemia that occurs when your body destroys cells that make intrinsic factor
  • Surgery that removes certain parts of your stomach or small intestine, such as some weight-loss surgeries
  • Taking antacids and other heartburn medicines for a long period of time
  • Abuse of "laughing gas" (nitrous oxide)

What are the symptoms for Vitamin B12 Deficiency Anemia?

You may not have symptoms. Symptoms may be mild.

Symptoms can include:

  • Diarrhea or constipation
  • Fatigue, lack of energy, or lightheadedness when standing up or with exertion
  • Loss of appetite
  • Pale skin
  • Feeling irritable
  • Shortness of breath, mostly during exercise
  • Swollen, red tongue or bleeding gums

If you have low vitamin B12 level for a long time, you can have nerve damage. Symptoms of nerve damage include:

  • Confusion or change in mental status (dementia) in severe cases
  • Problems concentrating
  • Psychosis (losing contact with reality)
  • Loss of balance
  • Numbness and tingling of hands and feet
  • Hallucinations

What are the current treatments for Vitamin B12 Deficiency Anemia?

Treatment depends on the cause of B12 deficiency anemia.

The goal of treatment is to increase your vitamin B12 level.

  • Treatment may include a shot of vitamin B12 once a month. If you have a very low level of B12, you may need more shots in the beginning. It is possible you may need shots every month for the rest of your life.
  • Some people may respond to treatment by taking vitamin B12 supplements by mouth.

Your provider will also recommend that you eat a variety of foods.

What is the outlook (prognosis) for Vitamin B12 Deficiency Anemia?

People with this type of anemia often do well with treatment.

Long-term vitamin B12 deficiency can cause nerve damage. This may be permanent if you do not start treatment within 6 months of when your symptoms begin.

Vitamin B12 deficiency anemia most often responds well to treatment. It will likely get better when the underlying cause of the deficiency is treated.

What are the possible complications for Vitamin B12 Deficiency Anemia?

A woman with a low B12 level may have a false positive Pap smear. This is because vitamin B12 deficiency affects the way certain cells (epithelial cells) in the cervix look.

When should I contact a medical professional for Vitamin B12 Deficiency Anemia?

Call your provider if you have any of the symptoms of anemia.

How do I prevent Vitamin B12 Deficiency Anemia?

You can prevent anemia caused by a lack of vitamin B12 by eating a well-balanced diet.

Shots of vitamin B12 can prevent anemia if you've had a surgery known to cause vitamin B12 deficiency.

Early diagnosis and prompt treatment can reduce or prevent complications related to a low vitamin B12 level.

Megaloblastic anemia - view of red blood cells
Hypersegmented PMN (Close-up)


Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 39.

Means RT. Approach to the anemias. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 149.

Perez DL, Murray ED, Price BH. Depression and psychosis in neurological practice. In: Daroff RB, Jankovic J, Mazziotta JC, Pomeroy SL, eds. Bradley's Neurology in Clinical Practice. 7th ed. Philadelphia, PA: Elsevier; 2016:chap 10.

  • Condition: Cerebral Venous Sinus Thrombosis Caused by Nitrous Oxide (NO) Abuse
  • Journal: BMJ case reports
  • Treatment Used: Vitamin B12 Supplementation, Low-Molecular-Weight Heparin, and Dabigatran
  • Number of Patients: 1
  • Published —
This case report describes a 24-year-old man diagnosed with cerebral venous sinus thrombosis (clot) as a complication of nitrous oxide (NO) abuse treated with vitamin B12 supplementation, low-molecular-weight-heparin, and dabigatran.
  • Journal: Journal of tropical pediatrics
  • Published —
Plasma and Urinary Amino Acid Profile in Children with Infantile Tremor Syndrome.
Clinical Trial
  • Status: Active, not recruiting
  • Phase: N/A
  • Intervention Type: Dietary Supplement
  • Participants: 24
  • Start Date: December 17, 2018
Factors Affecting Colonic Folate Absorption and Metabolism in Humans
Clinical Trial
  • Status: Recruiting
  • Phase: N/A
  • Intervention Type: Dietary Supplement
  • Participants: 80
  • Start Date: January 20, 2020
Nutrition, Vision, and Cognition in Sport Study: Beef