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Vitamin B12

What is it?

Vitamin B12 is a vitamin. It can be found in foods such as meat, fish, and dairy products. It can also be made in a laboratory.

Vitamin B12 is used for treating and preventing vitamin B12 deficiency, a condition in which vitamin B12 levels in the blood are too low. It is also used to treat pernicious anemia, a serious type of anemia that is due to vitamin B12 deficiency and is found mostly in older people. For this purpose, people use either a supplement that is taken by mouth or a gel that is applied inside the nose.

Vitamin B12 is also used for memory loss; Alzheimer’s disease; boosting mood, energy, concentration and the immune system; and slowing aging. It is also used for heart disease, lowering high homocysteine levels (which may contribute to heart disease), male infertility, diabetes, sleep disorders, depression, mental disorders, weak bones (osteoporosis), swollen tendons, AIDS, inflammatory bowel disease, asthma, allergies, a skin disease called vitiligo, preventing cervical and other cancers, and skin infections.

Some people use vitamin B12 for amyotrophic lateral sclerosis (Lou Gehrig’s disease), multiple sclerosis, preventing the eye disease age-related macular degeneration (AMD), Lyme disease and gum disease. It is also used for ringing in the ears, bleeding, liver and kidney disease, and for protection against the poisons and allergens in tobacco smoke.

Vitamin B12 is applied to the skin either alone or in combination with avocado oil for psoriasis and eczema.

Vitamin B12 is frequently used in combination with other B vitamins in various vitamin B complex products.

How effective is it?

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

The effectiveness ratings for VITAMIN B12 are as follows:

Effective for...

  • Treatment and prevention of vitamin B12 deficiency, and diseases caused by low vitamin B12 levels.
  • Treatment of pernicious anemia.

Likely effective for...

  • Reducing a condition related to heart disease called “hyperhomocysteinemia” when taken with folic acid and vitamin B6.

Possibly effective for...

  • Age-related macular degeneration (AMD). Some research shows that taking vitamin B12 with other vitamins including folic acid and vitamin B6 might help prevent getting the eye disease called age-related macular degeneration.

Possibly ineffective for...

  • Sleep disorders.
  • Preventing another stroke.
  • Improving thinking and memory in people aged 65 and older, when used in combination with vitamin B6 and folic acid.

Insufficient evidence to rate effectiveness for...

  • Shaky-leg syndrome. There are some reports that one form of vitamin B12 (cyanocobalamin) can help relieve tremor due to shaky-leg syndrome.
  • Eczema (atopic dermatitis). Limited research shows that applying a specific vitamin B12 0.07% cream (Regividerm) to the affected area twice daily reduces the extent and severity of eczema.
  • Alzheimer’s disease. Limited research suggests that higher vitamin B12 intake does not seem to prevent Alzheimer’s disease.
  • Canker sores. Preliminary research shows that taking vitamin B12 1000 mcg under the tongue (sublingually) might help reduce the number of canker sore outbreaks, length of outbreaks, and pain caused by the canker sores.
  • Cervical cancer. Increasing vitamin B12 intake from food and supplements, along with taking folic acid, thiamine, and riboflavin, might help to prevent cervical cancer.
  • Breast cancer. There is no evidence that dietary vitamin B12 alone reduces the risk of breast cancer.
  • Lung cancer. Preliminary evidence suggests that there is no relationship between levels of vitamin B12 in the blood and lung cancer.
  • Allergies.
  • Aging.
  • Chronic fatigue syndrome (CFS).
  • Preventing re-blockage of blood vessels after heart artery dilation (balloon angioplasty).
  • Fatigue or tiredness.
  • Diabetes.
  • Heart disease.
  • Lyme disease.
  • Immune system problems.
  • Memory problems.
  • Multiple sclerosis.
  • High cholesterol.
  • Psoriasis.
  • Other conditions.
More evidence is needed to rate vitamin B12 for these uses.

How does it work?

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Vitamin B12 is required for the proper function and development of the brain, nerves, blood cells, and many other parts of the body.

Are there safety concerns?

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Vitamin B12 is LIKELY SAFE for most people when taken by mouth or when the prescription-only, injectable product is used correctly. In some people, vitamin B12 might cause diarrhea, blood clots, itching, serious allergic reactions, and other side effects.

Vitamin B12 also appears to be safe when used on the skin for psoriasis. Mild itching has been reported in one person who used a specific avocado oil plus vitamin B12 cream for psoriasis.

Special precautions & warnings:

Pregnancy and breast-feeding: Vitamin B12 is LIKELY SAFE for pregnant or breast-feeding women when taken by mouth in the amounts recommended. The recommended amount for pregnant women is 2.6 mcg per day. Breast-feeding women should take no more than 2.8 mcg per day. Don’t take larger amounts. The safety of larger amounts is unknown.

High numbers of red blood cells (polycythemia vera): The treatment of vitamin B12 deficiency can unmask the symptoms of polycythemia vera.

Abnormal red blood cells (megaloblastic anemia): Megaloblastic anemia is sometimes corrected by treatment with vitamin B12. But this can have very serious side effects. Don’t attempt vitamin B12 therapy without close supervision by your healthcare provider.

Leber’s disease, a hereditary eye disease: Do not take vitamin B12 if you have this disease. It can seriously harm the optic nerve, which might lead to blindness.

Allergy or sensitivity to cobalt or cobalamin: Do not use vitamin B12 if you have this condition.

Are there interactions with medications?

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Do not take this combination.

Vitamin B12 is important for producing new blood cells. Chloramphenicol might decrease new blood cells. Taking chloramphenicol for a long time might decrease the effects of vitamin B12 on new blood cells. But most people only take chloramphenicol for a short time, so this interaction isn't a big problem.

Are there interactions with herbs and supplements?

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Folic acid
Folic acid, particularly in large doses, can cover up vitamin B12 deficiency, and cause serious health effects. Be sure that your healthcare provider checks your vitamin B12 levels before you start taking folic acid.

Potassium supplements can reduce absorption of vitamin B12 in some people and might contribute to vitamin B12 deficiency.

Vitamin C
Early research suggests that vitamin C supplements can destroy dietary vitamin B12. It isn't known whether this interaction is important, but to stay on the safe side, take vitamin C supplements at least 2 hours after meals.

Are there interactions with foods?

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Heavy drinking for at least a two-week period can decrease vitamin B12 absorption from the gastrointestinal tract.

What dose is used?

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The following doses have been studied in scientific research:


The typical general supplemental dose of vitamin B12 is 1-25 mcg per day.

The recommended dietary allowances (RDAs) of vitamin B12 are: Infants 0-6 months, 0.4 mcg; infants 7-12 months, 0.5 mcg; children 1-3 years, 0.9 mcg; children 4-8 years, 1.2 mcg; children 9-13 years, 1.8 mcg; older children and adults, 2.4 mcg; pregnant women, 2.6 mcg; and breast-feeding women, 2.8 mcg. Because 10% to 30% of older people do not absorb food-bound vitamin B12 efficiently, those over 50 years should meet the RDA by eating foods fortified with B12 or by taking a vitamin B12 supplement. Supplementation of 25-100 mcg per day has been used to maintain vitamin B12 levels in older people.
  • For vitamin B12 deficiency or pernicious anemia: cyanocobalamin doses of 300-10,000 mcg (microgram) daily have been used. However, some evidence suggests that the most effective oral dose is between 647-1032 mcg/day.
  • For high blood levels of homocysteine: vitamin B12 500 mcg in combination with 0.5-5 mg folic acid and 16.5 mg pyridoxine has been used.
  • For preventing age-related macular degeneration (AMD): vitamin B12 1 mg, folic acid 2.5 mg, and pyridoxine 50 mg daily has been studied.
  • For atopic dermatitis (eczema): a specific vitamin B12 0.07% cream (Regividerm) applied twice daily has been used.
  • For psoriasis: a specific cream (Regividerm, Regeneratio Pharma AG, Wuppertal, Germany) containing avocado oil plus vitamin B12 0.7 mg/gram applied for 12 weeks twice daily has been used.

Other names

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B-12, B12, B Complex Vitamin, Bedumil, Cobalamin, Cobalamine, Cobamin, Cobamine, Complexe Vitaminique B, Cyanocobalamin, Cyanocobalamine, Cyanocobalaminum, Cycobemin, Hydroxocobalamin, Hydroxocobalamine, Hydroxocobalaminum, Hydroxocobemine, Hydroxocobémine, Idrossocobalamina, Methylcobalamin, Méthylcobalamine, Vitadurin, Vitadurine, Vitamina B12, Vitamine B12.


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To learn more about how this article was written, please see the Natural Medicines Comprehensive Database methodology.methodology (


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To see all references for the Vitamin B12 page, please go to

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