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Vitamin B12

A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. It is found in liver, meat, eggs, poultry, shellfish, milk, and milk products.

PubMed Health Glossary
(Source: NIH - National Cancer Institute)

About Vitamin B12

A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. Vitamin B12 helps make red blood cells, DNA, RNA, energy, and tissues, and keeps nerve cells healthy. It is found in liver, meat, eggs, poultry, shellfish, milk, and milk products.

Vitamin B12 is water-soluble (can dissolve in water) and must be taken in every day. Not enough vitamin B12 can cause certain types of anemia (a condition in which the number of red blood cells is below normal) and neurologic disorders.

It is being studied with folate in the prevention and treatment of some types of cancer. Also called cobalamin and cyanocobalamin. NIH - National Cancer Institute

What works? Research summarized

Evidence reviews

Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency

Vitamin B12 deficiency can cause anaemia and neurological complications. Vitamin B12 is rarely prescribed in the oral form in most countries. Two randomised controlled studies were included in this review. The trials recruited a total of 108 participants and followed up 93 of these from 90 days to four months. The evidence derived from these limited studies suggests that high oral doses of B12 (1000 mcg and 2000 mcg) could be as effective as intramuscular administration in achieving haematological and neurological responses.

No evidence of the efficacy of vitamin B12 supplementation for cognitive function

Vitamin B12 is essential for maintaining normal function of the nervous system, but the relationship between vitamin B12 and cognitive function is not fully understood. From the three studies involving people with dementia or cognitive impairment and low blood levels of vitamin B12 eligible for inclusion in this review there was no statistically significant effect of vitamin B12 supplementation on cognition. The variety of measurement scales used to assess outcomes and uncertainty about diagnostic criteria for vitamin B12 deficiency create difficulties in pooling the results of trials.

No evidence that folic acid with or without vitamin B12 improves cognitive function of unselected elderly people with or without dementia. Long‐term supplementation may benefit cognitive function of healthy older people with high homocysteine levels

In the economically developed world, folate deficiency is one of the commonest vitamin deficiencies. Several reports suggest a higher prevalence of various psychiatric disorders in elderly people with folate deficiency. There is interest in whether dietary supplements of folic acid (an artificial chemical analogue of naturally occurring folates) can improve cognitive function of people at risk of cognitive decline associated with ageing or dementia, whether by affecting homocysteine metabolism or through other mechanisms. Eight trials met the criteria for inclusion. It was not possible to pool the data because the trials studied different populations, tested folic acid in different doses, and used different outcome measures. There were two trials of folic acid in conjunction with B12. The analysis showed significant benefit of folic acid over placebo in some measures of cognition in a long‐term trial recruiting elderly people with high homocysteine levels from a general population. In one pilot trial, 1 mg/day of folic acid was associated with significant improvement in behavioural response to cholinesterase inhibitors in people with Alzheimer's disease.

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Summaries for consumers

Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency

Vitamin B12 deficiency can cause anaemia and neurological complications. Vitamin B12 is rarely prescribed in the oral form in most countries. Two randomised controlled studies were included in this review. The trials recruited a total of 108 participants and followed up 93 of these from 90 days to four months. The evidence derived from these limited studies suggests that high oral doses of B12 (1000 mcg and 2000 mcg) could be as effective as intramuscular administration in achieving haematological and neurological responses.

No evidence of the efficacy of vitamin B12 supplementation for cognitive function

Vitamin B12 is essential for maintaining normal function of the nervous system, but the relationship between vitamin B12 and cognitive function is not fully understood. From the three studies involving people with dementia or cognitive impairment and low blood levels of vitamin B12 eligible for inclusion in this review there was no statistically significant effect of vitamin B12 supplementation on cognition. The variety of measurement scales used to assess outcomes and uncertainty about diagnostic criteria for vitamin B12 deficiency create difficulties in pooling the results of trials.

No evidence that folic acid with or without vitamin B12 improves cognitive function of unselected elderly people with or without dementia. Long‐term supplementation may benefit cognitive function of healthy older people with high homocysteine levels

In the economically developed world, folate deficiency is one of the commonest vitamin deficiencies. Several reports suggest a higher prevalence of various psychiatric disorders in elderly people with folate deficiency. There is interest in whether dietary supplements of folic acid (an artificial chemical analogue of naturally occurring folates) can improve cognitive function of people at risk of cognitive decline associated with ageing or dementia, whether by affecting homocysteine metabolism or through other mechanisms. Eight trials met the criteria for inclusion. It was not possible to pool the data because the trials studied different populations, tested folic acid in different doses, and used different outcome measures. There were two trials of folic acid in conjunction with B12. The analysis showed significant benefit of folic acid over placebo in some measures of cognition in a long‐term trial recruiting elderly people with high homocysteine levels from a general population. In one pilot trial, 1 mg/day of folic acid was associated with significant improvement in behavioural response to cholinesterase inhibitors in people with Alzheimer's disease.

See all (19)

More about Vitamin B12

Photo of an adult

Also called: Cobalamin, Cyanocobalamin

Other terms to know:
Anemia, Pernicious Anemia

Keep up with systematic reviews on Vitamin B12:

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