Vitamin B12 Deficiency

(Vitamin B12 Deficiency; Macrocytic Achylic Anemia)

Pronounced: Vite-ah-min bee-twelv di-fish-ens-ee


Vitamin B12 helps in red blood cell formation, production of DNA, and function of the nervous system.

Vitamin B12 deficiency can occur when the body needs more vitamin B12 than it receives from the diet. Alternatively, the condition may occur when the body is unable to use vitamin B12 from the diet. A shortage of vitamin B12 can lead to anemia. Anemia occurs when levels of red blood cells are abnormally low and there is insufficient delivery of oxygen by red blood cells from the lungs to the cells of the body.

Red Blood Cells

Nucleus factsheet image
Copyright © Nucleus Medical Media, Inc.

Causes    TOP

There are many causes of vitamin B12 deficiency, such as:

  • Removal of part of the small intestine or stomach
  • Poor absorption of B12 in older adults
  • Long-term use of certain acid-reducing stomach medications:
    • H2 blockers
    • Proton pump inhibitors
  • Atrophic gastritis (inflammation of the stomach) due to:
  • Disorders affecting vitamin absorption:
  • Inadequate intake of vitamin B12
    • Long-term veganism or vegetarianism
    • Breastfed infants of vegan or vegetarian mothers
    • Poor nutrition
    • Inadequate nutrition for a pregnant woman
    • Chronic alcohol abuse
  • Chronic intestinal conditions that lead to malabsorption
  • Inflammation of the intestine due to radiation treatment
  • Malnutrition
  • Increased need of vitamin B12:
  • Metabolic disorders:

Risk Factors    TOP

The following factors increase your chance of developing vitamin B12 deficiency:

  • Alcoholism
  • Use of certain drugs:
    • Biguanides for diabetes
    • Cimetidine
    • Acid-reducing medications
  • Strict vegan or vegetarian diet

Symptoms    TOP

The symptoms of pernicious anemia can vary from person-to-person. Symptoms may change or worsen over time.

Symptoms can include:

  • Sensation of pins and needles in feet or hands
  • Stinging sensation on the tongue or smooth red tongue
  • Substantial weight loss
  • Tiredness
  • Paleness
  • Altered sense of taste
  • Confusion
  • Depression
  • Impaired sense of balance, especially in the dark
  • Inability to sense vibrations in feet or legs
  • Lightheadedness when changing to standing position
  • Rapid heart rate

Diagnosis    TOP

You will be asked about your symptoms and medical history. A physical exam will be done. Tests may include the following:

  • Complete blood count (CBC)—a count of the number of red and white blood cells in a blood sample
  • Vitamin B12 level—a test that measures the amount of vitamin B12 in the blood
  • Methylmalonic acid (MMA) level
  • Homocysteine level
  • Schilling test—a test in which a small amount of radiation is used to assess the absorption of vitamin B12 deficiency
  • Folate level—a measurement of the amount of a B vitamin called folic acid
  • Intrinsic factor antibodies—this test helps to determine pernicious anemia as the cause of symptoms

Treatment    TOP

Talk with your doctor about the best treatment plan for you. Treatment options include the following:

Oral Vitamin B12 Supplement

This treatment consists of high doses of an oral vitamin B12 supplement.

Vitamin B12 Injections

The doctor may advise injections of vitamin B12 into a muscle. Injections of vitamin B12 may be given frequently at first. When blood tests show improvement, the injections may be given on a monthly basis.

Treatment with Antibiotics    TOP

This type of medication may be needed in cases where bacterial overgrowth in the intestines exists. The bacteria compete with the body to absorb the vitamin B12 in the intestines.

Intranasal Vitamin B12    TOP

The doctor may advise a supplement of vitamin B12 that is placed in the nose.

Prevention    TOP

To help reduce your chances of developing a deficiency of vitamin B12, take the following steps:

  • Eat foods that are a source of vitamin B12, such as:
    • Eggs, milk, cheese, and milk products
    • Meat, fish, shellfish, and poultry
    • Soy-based meat substitutes
    • Some soy and rice beverages
  • Avoid long-term over-consumption of alcohol.
  • As directed by your doctor, take a daily supplement containing vitamin B12.
  • As directed by your doctor, give vitamin B12 to your breastfed baby if you are a vegan or vegetarian.
  • Undergo testing if your doctor suspects you have a bacterial infection.
  • Have your doctor monitor your health closely if you are taking certain medications:
    • Biguanides
    • Cimetidine
    • Acid-reducing medications


Family Doctor—American Academy of Family Physicians
National Institutes of Health Office of Dietary Supplements


College of Family Physicians of Canada


Food sources of vitamin B12. Dietitians of Canada website. Available at: Accessed November 7, 2017.
Pernicious anemia. EBSCO DynaMed Plus website. Available at: Updated May 17, 2017. Accessed November 7, 2017.
Vitamin B12. American Association of Clinical Chemistry—Lab Tests Online website. Available at:
...(Click grey area to select URL)
Updated April 24, 2015. Accessed November 7, 2017.
Vitamin B12. EBSCO DynaMed Plus website. Available at: Updated November 6, 2017. Accessed November 7, 2017.
Vitamin B12 deficiency. EBSCO DynaMed Plus website. Available at: Updated December 4, 2015. Accessed November 7, 2017.
Last reviewed November 2017 by EBSCO Medical Review BoardDianne Scheinberg Rishikof MS, RD, LDN
Last Updated: 12/20/2014

EBSCO Information Services is fully accredited by URAC. URAC is an independent, nonprofit health care accrediting organization dedicated to promoting health care quality through accreditation, certification and commendation.

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

To send comments or feedback to our Editorial Team regarding the content please email us at Our Health Library Support team will respond to your email request within 2 business days.