Megaloblastic macrocytic anemia; Cobalamin 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.
Your body needs vitamin B12 to make red blood cells. In order to provide vitamin B12 to your cells:
Certain health conditions can make it difficult for your body to absorb enough vitamin B12. They include:
A lack of vitamin B12 may be due to dietary factors, including:
You may not have symptoms. Symptoms may be mild.
Symptoms may include:
If you have low vitamin B12 level for a long time, it can cause nerve damage. Symptoms of nerve damage include:
The health care provider will perform a physical exam. This may reveal problems with your reflexes or sensations.
Tests that may be done include:
Other procedures that may be done include:
Treatment depends on the cause of B12 deficiency anemia. The goal of treatment is to increase your vitamin B12 level.
For people who have a low level of B12 due to a restricted vegetarian diet, taking B12 pills may resolve the issue.
For people with a health condition that causes B12 deficiency, treatment may include a shot of vitamin B12, often 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 regularly for the rest of your life.
Your provider will also recommend that you eat a variety of foods.
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 promptly after your symptoms begin. If nerve damage is severe or long-lasting, some damage may be permanent.
Vitamin B12 deficiency anemia most often responds well to treatment. It will likely get better when the underlying cause of the deficiency is treated.
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.
Contact your provider if you have any of the symptoms of anemia.
Eating a well-balanced diet can help ensure you get enough vitamin B12 from the foods you eat. However, it can't prevent anemia in people with certain health conditions that prevent their body from using vitamin B12 properly.
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.
There is no evidence that taking B12 supplements will prevent or treat dementia, Alzheimer disease, or other health conditions such as heart disease.
Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 40.
Means Jr. RT. Approach to the anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 144.
National Institutes of Health website. Vitamin B12: fact sheet for health professionals. ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Updated March 26, 2024. Accessed August 17, 2024.
Stabler SP. Megaloblastic anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 150.
BACK TO TOPReview Date: 3/31/2024
Reviewed By: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 08/19/2024.
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06/01/2025
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