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Vitamins & minerals health centre

Vitamin B12 (cobalamin)

What is vitamin B12?

Vitamin B12 (cobalamin) plays a role in making DNA. Vitamin B12 also helps maintain healthy nerve cells and red blood cells.

Vitamin B12 uses

Vitamin B12 supplements can help people who have an actual deficiency. Low levels of vitamin B12 are more likely in people over 50. Vitamin B12 deficiency is also more common in those with certain conditions, including digestive problems and some types of anaemia. Low levels of vitamin B12 can cause fatigue, weakness, memory loss and other problems related to the nervous system.

Strict vegetarians are at risk of vitamin B12 deficiency. Pregnant women and nursing mothers who are vegetarian should talk to a doctor about vitamin B12 supplements. If infants do not get enough vitamin B12, they can suffer lasting neurological harm.

Vitamin B12 has been studied as a treatment for many diseases and conditions. These include fatigue, Alzheimer’s disease, heart disease, breast cancer, high cholesterol and sickle cell disease. However, the results have been inconclusive. Studies suggest that vitamin B12 does not help with stroke risk or lung cancer. In fact B12 may increase a person's risk of lung cancer. There is some evidence that vitamin B12 may help prevent cervical cancer though this is not proven.

Vitamin B12 dose and instructions for use

The NHS says adults need around 0.0015mg (1.5mcg) a day of vitamin B12.

Even at high doses, vitamin B12 seems fairly safe. Experts have not found a specific dose of vitamin B12 that is dangerous. The NHS says that taking 2 milligrams (2000mcg) or less of vitamin B12 supplements a day is unlikely to cause adults any harm.

Vitamin B12 Food Sources

Some good food sources of vitamin B12 are:

  • Fish and shellfish
  • Meat
  • Poultry and eggs
  • Dairy products
  • Fortified cereals

Generally, it is best to get vitamins from eating a balanced healthy diet, but doctors often suggest fortified foods and supplements for people over 50. As we age, it is harder for our bodies to absorb vitamin B12 from food.

Vitamin B12 supplement information

Vitamin B12 comes in tablets, capsules and other forms, including those placed under the tongue (sublingual). It is standard in multivitamin products. Doctors can also give it by injection. As with any supplement, keep vitamin B12 supplements in a cool, dry place, away from humidity and direct sunlight.

Unless vitamin B12 is specifically prescribed on its own, it is usually recommended to take B vitamin supplements along with vitamin B complex, which includes eight vitamins, including B12, plus thiamine (B1) riboflavin (B2), niacin (B3), folic acid, biotin, pantothenic acid and pyroxidine (B6).

Vitamin B12 warnings

  • Side-effects and risks. When vitamin B12 is taken at normal doses, side-effects are rare. High doses may cause acne. Allergies to vitamin B12 supplements have been reported and can cause swelling, itchy skin and shock.
  • Interactions. Drugs for acid reflux, diabetes and other conditions may make it harder for your body to absorb vitamin B12.

WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on March 30, 2017

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