In this Fact Sheet: Functions, Dietary Sources and Required Intakes
Vitamin B12 is a member of the B vitamin group, these are water soluble vitamins and play an important role in cell metabolism. B12 consists of a small group of compounds, (the cobalamins) and is necessary for the synthesis of red blood cells, the maintenance of the nervous system and for child development.
B12 is synthesised in nature by micro-organisms and foods derived from animals are a source of this vitamin because they eat other animal food, the internal production of B12 due to their intestinal bacteria (not present in humans) or by eating food contaminated with bacteria.
Diets which exclude all animal produce need to ensure that they obtain their recommended daily intake from other sources.
The primary functions of vitamin B12 (cyanocobalamin) are for:
- The formation of red blood cells and their roles
- Normal cell division
- Nerve structure and function
- The maintenance of normal blood homocysteine levels, together with folate and vitamin B6 (raised levels are a risk factor in cardiovascular disease).
The substance in our bodies needed for the absorption of B12 is known as intrinsic factor (mainly secreted from gastric parietal cells), a lack of this can also cause deficiency of the vitamin. The deficiency of B12 is due mostly to inherited/acquired defects resulting in malabsorption or the impaired transport of the vitamin within the body. A shortage of B12 can cause anaemia and neurological damage. B12 is also essential to the growth and development of a baby. The amount of B12 in the diet is of special concern within the elderly as deficiency occurs more frequently in older people. Disorders relating to B12 malabsorption are usually treated by either repeat injection or through oral supplementation.
Vitamin B12 can be stored in small amounts by the body (predominantly in the liver), with a normal amount being around 2-3mgs in adults (this amount is sufficient for 2 to 4 years). According to the British Nutrition Foundation, dietary deficiency is rare but it can sometimes be seen in vegans who obtain virtually no B12 in their diet.
The main foods which provide a source of vitamin B12 those derived from animals e.g. dairy products and eggs. For those individuals not eating any animal produce yeast extract is a good source of vitamin B12 along with other fortified/supplemented foods such as breakfast cereals, soya milks, soya/veggie burger products and also vegetable margarines.
Fermented products, such as tempeh and miso (obtained from fermented soya beans), shiitake mushrooms and algae (spirulina and nori) contain substances which are similar chemically to vitamin B12. However, as they do not work in the body in the same way as the active vitamin these foods cannot be relied upon as sources of vitamin B12.
Very young babies will get all the vitamin B12 they need from breast or formula milk. Later, vegetarian babies should obtain enough of this vitamin from dairy products and eggs. However it is particularly important to ensure that vegan babies get vitamin B12 from clearly labelled fortified foods such as soya formula (seek advice from a health professional prior to feeding), low-salt yeast extract and breakfast cereals.
According to the Food Standards Agency (FSA), the reference nutrient intake for Vitamin B12 in adults is 1.5 micrograms per day.
Any questions regarding this information sheet please contact firstname.lastname@example.org | Last updated May 2010