Medically reviewed on October 17, 2017
Vitamin B-12 (cobalamin) is a water-soluble vitamin that plays essential roles in red blood cell formation, cell metabolism, nerve function and the production of DNA.
Food sources of vitamin B-12 include poultry, meat, fish and dairy products. Vitamin B-12 is also added to some foods and is available as an oral supplement. Vitamin B-12 injections or nasal spray might be prescribed to treat vitamin B-12 deficiency.
Because your body is capable of storing several years' worth of vitamin B-12, deficiency is rare. However, if you follow a vegetarian or vegan diet, you might be prone to deficiency because plant foods don't contain vitamin B-12. Older adults and people with digestive tract conditions that affect absorption of nutrients also are susceptible to vitamin B-12 deficiency.
Left untreated, a vitamin B-12 deficiency can lead to anemia, fatigue, muscle weakness, intestinal problems, nerve damage and mood disturbances.
The recommended daily amount of vitamin B-12 for adults is 2.4 micrograms.
Research on the use of vitamin B-12 for specific activities and conditions shows:
- Heart and blood vessel disease. Vitamin B-12, in combination with vitamin B-6 and folate (vitamin B-9), has been shown to control high levels of homocysteine in the blood. Elevated homocysteine might increase your risk of diseases of the heart and blood vessels (cardiovascular disease). Despite this benefit, there's no evidence to show that vitamin B-12 supplements prevent heart disease.
- Dementia. Vitamin B-12 deficiency is associated with dementia and low cognitive function, but it's not clear whether vitamin B-12 supplements might help prevent or treat dementia.
- Athletic performance. Unless you have a vitamin B-12 deficiency, there's no evidence that vitamin B-12 supplements will boost your energy or make you a better athlete.
Most people get enough vitamin B-12 from a balanced diet. However, older adults, vegetarians and people who have conditions that affect their ability to absorb vitamin B-12 from foods might benefit from the use of oral supplements.
Vitamin B-12 supplements also are recommended for women who are pregnant or breast-feeding exclusively and follow vegetarian or vegan diets.
Safety and side effects
When taken at appropriate doses, vitamin B-12 supplements are generally considered safe. While the recommended daily amount of vitamin B-12 for adults is 2.4 micrograms, you can safely take higher doses. Your body absorbs only as much as it needs, and any excess passes through your urine.
High doses of vitamin B-12, such as those used to treat a deficiency, might cause:
Possible interactions include:
- Aminosalicylic acid. Taking this drug used to treat digestive problems might reduce your body's absorption of vitamin B-12.
- Colchicine (Colcrys, Mitigare). Taking this anti-inflammatory drug used to prevent and treat gout attacks might decrease your absorption of vitamin B-12.
- Metformin (Glumetza, Glucophage, Fortamet). Taking this diabetes drug might reduce your absorption of vitamin B-12.
- Proton pump inhibitors. Taking omeprazole (Prilosec), lansoprazole (Prevacid) or other stomach acid-reducing drugs might decrease your absorption of vitamin B-12.
- Vitamin C (ascorbic acid) supplements. Taking vitamin B-12 with vitamin C might reduce the available amount of vitamin B-12 in your body. To avoid this interaction, take vitamin C two or more hours after taking a vitamin B-12 supplement.
Your doctor might recommend changing drugs or timing doses to offset any potential interactions.