Vitamin B12 (cobalamin) is a water-soluble vitamin needed for red blood cell formation, nerve function and DNA synthesis. It also acts as a cofactor for enzymes that convert homocysteine to methionine and that support energy metabolism from fats and proteins.

Dietary B12 is naturally found only in animal foods such as meat, fish, eggs and dairy. In the stomach it is released from food proteins and binds to intrinsic factor, which allows absorption in the small intestine. This pathway can become less efficient with age, and absorption is lower in people who take certain medicines for reflux. A small amount can also be absorbed passively without intrinsic factor, which is how higher oral doses work. Common supplement forms are cyanocobalamin, methylcobalamin and adenosylcobalamin (see NIH Office of Dietary Supplements, Vitamin B12 fact sheet). The liver stores B12 for years.

• Helps maintain energy levels when dietary intake is inadequate
• Helps relieve tiredness and fatigue when due to a vitamin B12 deficiency
• Helps support normal red blood cell formation
• Helps maintain healthy nervous system function
• Helps support healthy homocysteine metabolism

Which form of vitamin B12 is best?

Both cyanocobalamin and methylcobalamin are used effectively by the body. Cyanocobalamin is stable and widely studied, while methylcobalamin is a naturally occurring form some people prefer. The best choice depends on your preference and your healthcare professional's advice.

Who might need extra vitamin B12?

People who eat little or no animal food, such as vegans, and older adults often have lower intakes or absorption. If you are unsure, a blood test through your doctor can check your levels.

Vitamin B12 is generally well tolerated. Tell your healthcare professional if you take metformin or reflux medicines, as these can reduce B12 absorption. Always read the label and use only as directed.

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