Overview

Vitamin B-12 (cobalamin) plays an essential role in red blood cell formation, cell metabolism, nerve function and the production of DNA, the molecules inside cells that carry genetic information.

Food sources of vitamin B-12 include poultry, meat, fish and dairy products. Vitamin B-12 is also added to some foods, such as fortified breakfast cereals, and is available as an oral supplement. Vitamin B-12 injections or nasal spray might be prescribed to treat vitamin B-12 deficiency.

Vitamin B-12 deficiency is not common in the U.S. However, people who follow a vegetarian or vegan diet 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 (mcg). Most people can get enough vitamin B-12 in the foods they eat. But people who follow a vegetarian or vegan diet should eat nutritional yeast and other foods fortified with vitamin B-12. Or they can take a low-dose multivitamin that includes 2.4 mcg of vitamin B-12. Higher doses are suggested only in those with a vitamin B-12 deficiency.

What the research says

Research on the use of vitamin B-12 for specific activities and conditions shows:

• Heart and blood vessel disease. Researchers had previously believed that vitamin B-12, when combined with folic acid (vitamin B-9) and vitamin B-6, might prevent diseases of the heart and blood vessels by reducing the levels of an amino acid in the blood (homocysteine). However, studies show that the combination of these vitamins doesn’t seem to reduce the risk or severity of cardiovascular disease and stroke.
• 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.

Our take

Generally safe

Most people get enough vitamin B-12 from a balanced diet. However, older adults, vegetarians, vegans 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 breastfeeding 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, higher doses have been found to be safe. 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:

• Headache
• Nausea and vomiting
• Diarrhea
• Fatigue or weakness
• Tingling sensation in hands and feet

Interactions

Possible interactions include:

• Aminosalicylic acid (Paser). Taking this drug used to treat digestive problems might reduce your body’s ability to absorb vitamin B-12.
• Colchicine (Colcrys, Mitigare, Gloperba). Taking this anti-inflammatory drug used to prevent and treat gout attacks might decrease your body’s ability to absorb vitamin B-12.
• Metformin (Glumetza, Fortamet, others). Taking this diabetes drug might reduce your body’s ability to absorb vitamin B-12.
• Proton pump inhibitors. Taking omeprazole (Prilosec), lansoprazole (Prevacid) or other stomach acid-reducing drugs might decrease your body’s ability to absorb 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.