Vitamin B12 Deficiency
(Vitamin B12 Deficiency; Macrocytic Achylic Anemia)
Pronounced: Vite-ah-min bee-twelv di-fish-ens-ee
by Monique Kahn, MS, RD
Vitamin B12 has many important roles in the body. It helps to make red blood cells, build DNA, and maintains a protective coating around the nerves.
Vitamin B12 deficiency is a shortage of available B12 in the body. It can occur when:
A deficiency in vitamin B12 can lead to:
There are many causes of vitamin B12 deficiency, such as:
Risk Factors ▲
The following factors increase your chance of developing vitamin B12 deficiency:
The symptoms can vary from person-to-person and may change or worsen over time. Symptoms can include:
You will be asked about your symptoms and medical history. A physical exam will be done. Tests may include the following:
Treatment options include the following:
Oral Vitamin B12 Supplement
Daily high doses of an oral vitamin B12 supplement may help improve levels in the body. These dosages should only be given under a doctor's care.
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.
Intranasal Vitamin B12 ▲
This form of vitamin B12 supplement is as a spray through the nose.
Treatment with Antibiotics ▲
A bacterial overgrowth in the intestines can slow or stop the absorption of B12. Antibiotics may help to control the bacteria and improve vitamin levels in the body.
To help reduce your chances of developing a deficiency of vitamin B12, take the following steps:
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: https://www.dietitians.ca/Your-Health/Nutrition-A-Z/Vitamins/Food-Sources-of-Vitamin-B12.aspx. Accessed November 7, 2017.
Pernicious anemia. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T116294/Pernicious-anemia . Updated May 17, 2017. Accessed November 7, 2017.
Vitamin B12. American Association of Clinical Chemistry—Lab Tests Online website. Available at:
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Updated April 24, 2015. Accessed November 7, 2017.
Vitamin B12. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T233168/Vitamin-B12 . Updated November 6, 2017. Accessed November 7, 2017.
Vitamin B12 deficiency. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T116899 . Updated December 4, 2015. Accessed November 7, 2017.
Last reviewed November 2018 by EBSCO Medical Review Board Dianne Scheinberg Rishikof MS, RD, LDN
Last Updated: 2/6/2018
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