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Vitamin B12 Deficiency

Also indexed as: Pernicious Anemia


Your body relies on B12 for healthy blood. Too little of this vital vitamin can lead to anemia and other health issues. According to research or other evidence, the following self-care steps may be helpful:

What you need to know

  • Get your B12
  • Manage mild deficiency with over-the-counter vitamin B12 supplements
  • Add vitamins to your vegan diet
  • If you follow a strict vegan diet, take a daily B12 supplement of at least 2.4 mcg

These recommendations are not comprehensive and are not intended to replace the advice of your doctor or pharmacist. Continue reading the full vitamin B12 deficiency article for more in-depth, fully-referenced information on medicines, vitamins, herbs, and dietary and lifestyle changes that may be helpful.

About vitamin B12 deficiency

An abnormally low level of vitamin B12 (cobalamin) is a factor in many disorders.

The absorption of dietary vitamin B12 occurs in the small intestine and requires a secretion from the stomach known as intrinsic factor. If intrinsic factor is deficient, absorption of vitamin B12 is severely diminished. Vitamin B12 deficiency impairs the body’s ability to make blood, accelerates blood cell destruction, and damages the nervous system. The result is pernicious anemia (PA). In the classical definition, PA refers only to B12 deficiency anemia caused by a lack of intrinsic factor.

True PA is probably an autoimmune disease. The immune system destroys cells in the stomach that secrete intrinsic factor. Many people with PA have both chronic inflammation of the stomach lining, called atrophic gastritis, and antibodies that fight their intrinsic factor-secreting cells.1

The term pernicious anemia is sometimes used colloquially to refer to any anemia caused by vitamin B12 deficiency. Vitamin B12 deficiency can be due to malabsorption of dietary B12 despite normal levels of intrinsic factor. For example, celiac disease and Crohn’s disease may cause B12 malabsorption, which can lead to anemia. Less common causes of B12 deficiency include gastrointestinal surgery, pancreatic disease, intestinal parasites, and certain drugs. Pregnancy, hyperthyroidism, and advanced stages of cancer may increase the body’s requirement for B12, sometimes leading to a deficiency state.

Low stomach acid, known as hypochlorhydria, interferes with the absorption of B12 from food but not from supplements. Aging is associated with a decrease in the normal secretion of stomach acid. As a result, some older people with normal levels of intrinsic factor and with no clear cause for malabsorption will become vitamin B12-deficient unless they take at least a few micrograms per day of vitamin B12 from supplements.

Caution: PA is a serious medical condition. When fatigue, often the first symptom of PA, is present, a qualified healthcare practitioner should be consulted. Symptoms of PA can be caused by other conditions, none of which would respond to vitamin B12 supplementation. Moreover, if true vitamin B12 deficiency exists, the cause—lack of intrinsic factor, general malabsorption conditions, lack of stomach acidity, or dietary deficiency—must also be properly diagnosed by examination and blood tests before the appropriate treatment can be determined.

Product ratings for pernicious anemia

Science Ratings Nutritional Supplements Herbs

Vitamin B12 (cobalamin)


B-Complex (for prevention of deficiency in people with low stomach acid)

Multivitamin containing vitamin B12 (for prevention of deficiency in people with low stomach acid)

3Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

What are the symptoms?

Symptoms of severe vitamin B12 deficiency (regardless of the cause) may include burning of the tongue, fatigue, weakness, loss of appetite, intermittent constipation and diarrhea, abdominal pain, weight loss, menstrual symptoms, psychological symptoms, and nervous system problems, such as numbness and tingling in the feet and hands. Most symptoms can occur before the deficiency is severe enough to cause anemia. Healthcare professionals have a series of laboratory tests that can determine B12 deficiency at earlier stages that are not accompanied by anemia.

Medical options

Prescription drug treatment for some individuals includes lifelong intramuscular vitamin B12 injections preferably as cyanocobalamin or hydroxocobalamin.

Dietary changes that may be helpful

Vitamin B12 is found in significant amounts only in animal protein foods—meat and poultry, fish, eggs, and dairy products. Even small amounts of these foods supply sufficient amounts of vitamin B12 to provide enough for healthy people.

Except for vegans (vegetarians who also abstain from eggs, dairy, and other animal products), virtually no one in North America has a diet deficient in vitamin B12. Those who avoid animal protein foods can easily take vitamin B12 supplements instead. Strict vegans generally develop a dietary deficiency of vitamin B12, but it is often many years before a deficiency becomes severe enough to cause symptoms or to be diagnosed. Doctors recommend that all vegans supplement with vitamin B12.

People who lack intrinsic factor or have a malabsorption condition need to depend on high amounts of vitamin B12 from supplements and not the lower amounts found in food. Similarly, older people with a vitamin B12 deficiency due to a lack of stomach acid, but not a lack of intrinsic factor, cannot depend on food-based vitamin B12.

Tempeh, a fermented soybean product, provides some vitamin B12. However, the B12 content of tempeh is variable and insufficient to meet dietary B12 requirements.2 Small but inconsistent amounts of B12 also occur in seaweed and spirulina.3 4 Because of this variability, most doctors do not recommend vegetable sources of vitamin B12 to replenish deficient stores. No other vegetables provide vitamin B12, unless they are contaminated with fecal matter (e.g., fertilizer).

Lifestyle changes that may be helpful

Alcohol abuse can lead to gastritis and damage to the lining of the intestines, both of which can interfere with vitamin B12 absorption. If B12 deficiency is due to alcoholism, abstinence may prevent further impairment of B12 absorption.5

Vitamins that may be helpful

Normally, only 3 to 4 mcg per day of vitamin B12 is required to prevent dietary deficiency. If gastrointestinal function is normal, even these small amounts of vitamin B12 from oral supplementation can prevent deficiency in vegans.6 If a deficiency already exists, most doctors will recommend an initial vitamin B12 injection, then oral amounts ranging from 500 mcg to 1,000 mcg per day until symptoms subside; this is followed by a maintenance level of approximately 10 mcg per day to prevent future deficiencies.

In a person with true PA, initial B12 supplementation should begin with an injection given by a qualified healthcare professional. After blood abnormalities are reversed, maintenance supplementation can be successfully accomplished with oral vitamin B12 at 1,000 to 2,000 mcg (1 to 2 mg) per day and does not require further injections.7 In a person lacking intrinsic factor, only about 1% of this oral amount (10–20 mcg) will be absorbed, but that amount is more than sufficient to prevent future vitamin B12 deficiency.8 9 Many physicians are unaware of this well-researched option and thus unnecessarily recommend lifelong B12 injections.10

People with a vitamin B12 deficiency due to a malabsorption condition must have an appropriate treatment tailored to their individual needs by a healthcare professional. In older people who have inadequate absorption of vitamin B12 from food due to low stomach acid, prevention of deficiency can be achieved with small amounts of supplemental vitamin B12 found in B-complex and multivitamins. However, if a deficiency already exists in such people, a vitamin B12 injection is typically the initial treatment, followed by varying amounts of oral supplemental vitamin B12 depending on the extent of the deficiency.

Are there any side effects or interactions?
Refer to the individual supplement for information about any side effects or interactions.

Caution: Individuals with vitamin B12 deficiency must not take large amounts (greater than 800 mcg per day) of folic acid without the supervision of a doctor. At high levels, folic acid can mask the signs of vitamin B12 deficiency, potentially resulting in serious and irreversible nerve damage.


1. Beers MH, Berkow R, eds. The Merck Manual, 17th ed. Whitehouse Station, NJ: Merck and Co., Inc., 1999, 868.

2. Areekul S, Pattanamatum S, Cheeramakara C, et al. The source and content of vitamin B12 in the tempehs. J Med Assoc Thai 1990;73:152–6.

3. Dagnelie PC, van Staveren WA, van den Berg H. Vitamin B-12 from algae appears not to be bioavailable. Am J Clin Nutr 1991;53:695–7. Published erratum appears in Am J Clin Nutr 1991;53:988.

4. Rauma AL, Torronen R, Hanninen O, Mykkanen H. Vitamin B-12 status of long-term adherents of a strict uncooked vegan diet (“living food diet”) is compromised. J Nutr 1995;125:2511–5.

5. Gozzard DI. Experiences with dual protein bound aqueous vitamin B12 absorption test in subjects with low serum vitamin B12 concentrations. J Clin Pathol 1987;40:633–7.

6. Little DR. Ambulatory management of common forms of anemia. Am Fam Physician 1999;59:1598–604.

7. Kuzminski AM, Del Giacco EJ, Allen RH, et al. Effective treatment of cobalamin deficiency with oral cobalamin. Blood 1998;92:1191–8.

8. Kondo H. Haematological effects of oral cobalamin preparations on patients with megaloblastic anaemia. Acta Haematol 1998;9:200–5.

9. Berlin R, Berlin H, Brante G, Pilbrant A. Vitamin B12 body stores during oral and parenteral treatment of pernicious anaemia. Acta Med Scand 1978;204:81–4.

10. Lederle FA. Oral cobalamin for pernicious anemia. Medicine’s best kept secret? JAMA 1991;265(1):94–5.

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