Micronutrient: Vitamin B12
Type of Papers: Reports completed by expert consultations and published by the World Health Organization jointly with the Food and Agriculture Organization of the United Nations (FAO).
Note: Two WHO reports were summarized together as they contain much of the same information. See references below.
- Vitamin B12 (cobalamin) is involved in protein synthesis (specifically synthesis of the amino acid methionine) and is necessary for cell metabolism and survival.
- It functions closely with folate in protein synthesis and metabolism.
Prevalence of Deficiency:
- The worldwide prevalence of vitamin B12 deficiency is not known due to insufficient data. However, the World Health Organization estimates that millions of people across the world may be affected.
- The prevalence of vitamin B12 deficiency does not seem to vary systematically with country or geographic region. Several studies have assessed the prevalence of vitamin B12 deficiency, and examples of the prevalence rates include:
- Venezuela: 11-12% of preschool and school-age children
- Germany: 15% women of reproductive age
- U.S.: 0-3%
- Costa Rica: 5.3% lactating women
- Kenya: 40% school-age children
- Israel: 21% adults
- India: 46% adults
- Botswana (preschool children), Thailand (school-age children), Japan (adults): <1%
- The incidence of vitamin B12 deficiency seems to increase with age (due to gastric atrophy).
Risk Factors for Deficiency:
- Dietary factors: Low intake of animal products (e.g., meat, eggs, milk)
- Intakes are very low in economically disadvantaged groups or those who do not eat animal products for religious or other reasons
- High risk for deficiency in vegetarians (vegans) and even in lacto-ovo vegetarians (but at a lower risk)
- Malabsorption due to Helicobacter pylori, bacterial overgrowth, or gastric atrophy in the elderly
- Genetic disorders of vitamin B12 metabolism
- Indicators include: Low serum or plasma vitamin B12, elevated methylmalonic acid (MMA), and elevated plasma homocysteine.
- Low serum or plasma vitamin B12 should be the first indicator used to identify vitamin B12, and elevated methylmalonic acid (MMA) may be used to confirm the deficiency (if the assay is available). Elevated homocysteine is also a good predictor of vitamin B12 deficiency.
- MMA is specific to vitamin B12 in that it is not affected by other nutrient deficiencies. It may however be elevated for other reasons, such as renal insufficiency.
- Elevated homocysteine is not specific to vitamin B12 and is elevated due to folate deficiency or other vitamin B deficiencies.
- MMA and homocysteine are more expensive to measure than vitamin B12.
Dietary Sources and Bioavailability:
- Best Dietary Sources: Vitamin B12 is found almost exclusively in foods from animal tissues and products, including milk, butter, cheese, eggs, meat, and poultry (vitamin B12 is synthesized in the gut of animals and then distributed to animal tissues).
- Individuals who consume vegan diets (i.e., no animal products) are therefore at risk for vitamin B12 deficiency.
- Lacto-ovo vegetarians (those who consume eggs, milk, and other dairy products) are still at risk for inadequate vitamin B12; however the risk is lower compared to those with vegan diets.
Recommended Nutrient Intakes (µg/day): The following are the Recommended Nutrient Intakes (RNI) as defined by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization.
- Large amounts of supplemented vitamin B12 do not seem to have negative effects, but there is no benefit for large doses and should probably be avoided.
- Consumption of animal products is recommended to improve vitamin B12 status in individuals who consume vegan diets.
- In some communities where animal products are not consumed, the only source of vitamin B12 is from food contamination with microorganisms. Vegans living in communities with improved hygiene, and less food contamination, are at increased risk for vitamin B12 deficiency. Adding animal products to the diet is recommended in these communities.
- Supplementing schoolchildren in Kenya with meat and milk was effective in reducing the prevalence of vitamin B12 deficiency.
- Fermented vegetables may be a source of vitamin B12 for vegans, but more research is needed to determine its adequacy.
Health Consequences of Deficiency and Benefits of Intervention:
- Health Consequences of Deficiency:
- Consequences of vitamin B12 deficiency include megaloblastic anemia (low hemoglobin with large immature red blood cells), and demyelination of the central nervous system leading to various neurological disorders, poor memory and cognitive function
- In children, vitamin B12 deficiency has been associated with impaired cognition and growth. Examples include:
- School children in Guatemala City with low plasma vitamin B12 performed poorly on several cognitive assessments and had poorer school performance.
- Infants fed breast milk from vitamin B12 deficient mothers had failure to thrive, poor brain development, and in several cases, mental retardation.
- Health outcomes associated with interventions in infants in industrialized nations include:
- Fewer incidence of anemia and tremors
- Improved development in infants
Vitamin B12. Vitamin and mineral requirements in human nutrition. Report of a joint FAO/WHO expert consultation on human vitamin and mineral requirements, Bangkok, Thailand, 21–30 September 1998. 2nd ed. Geneva: World Health Organization, 2004:279-288.