'B' healthy

Vitamin B12 - what does it do?

Vitamin B12, or cobalamin, is one of the B group vitamins. Vitamin B12 is required for the production of red blood cells and in the formation of genetic material, DNA and RNA. It is used in the maintenance of myelin, a fatty substance which surrounds nerves and help them function properly. Vitamin B12 also works with other B vitamins in controlling levels of homocysteine; a component in blood that at high levels, can increase an individual’s risk of heart disease.

How much do we need?

Our requirements of vitamin B12 are very low - adults need only 1.5ìg per day, although breast-feeding women have slightly higher requirements (2ìg/day) - and deficiency of vitamin B12 is rare.

Who is at risk?

Because meat is the primary source of vitamin B12, vegetarians are more at risk of deficiency and must take care to include other sources in their diet, such as vitamin B12-enriched yeast or supplements. Also at risk of deficiency are those with a specific digestive disorder. A chemical produced in the stomach called intrinsic factor, is needed to absorb vitamin B12 but a small number of people can’t make this chemical and so can’t absorb dietary vitamin B12.

These people should be treated by their doctor with injections of the vitamin or take very high-dose supplements, under medical supervision. Elderly people may also have lower levels of intrinsic factor as their digestive processes gradually become less efficient and should be treated by a doctor.

What happens if you don't get enough?

Mild vitamin B12 deficiency can slightly impair brain and nerve function while long-term deficiency, as seen in those lacking intrinsic factor, leads to pernicious or megaloblastic anaemia. This anaemia can act as an early warning of deficiency; if allowed to continue, severe vitamin B12 deficiency can result in irreversible nerve damage.

Unfortunately, this megaloblastic anaemia can be masked by high levels of folate, meaning that a vitamin B12 deficiency may go unnoticed in a person with particularly high folate or folic acid intake. For this reason, high doses of folate (above current recommendations) should not be taken without first having vitamin B12 status examined.

Vitamin B12 is the only B vitamin of which we can store significant amounts in our bodies. Even a vegetarian who used to eat meat could have enough vitamin B12 to last 20 or 30 years! Despite this, the amount of vitamin B12 we absorb and use can change so we should be sure to eat vitamin B12-rich foods on a regular basis.

What are the best sources?

The best sources of vitamin B12 are beef, liver and lamb, which provide up to 100g in an average serving. Sardines, trout, salmon, tuna, eggs and cheese are also good sources. For those who don’t eat meat, fish or dairy products, yeats extract provides a small amount, but it’s also a good idea to eat fortified breakfast cereals

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