Vitamin B12

Vitamin B12 is a water-soluble vitamin. Water-soluble vitamins dissolve in water. After the body uses these vitamins, leftover amounts leave the body through the urine.

The body can store vitamin B12 for years in the liver.

Function

Vitamin B12, like the other B vitamins, is important for protein metabolism. It helps in the formation of red blood cells and in the maintenance of the central nervous system.

Food Sources

Vitamin B12 is found naturally in a wide variety of animal proteins. Plant foods have no vitamin B12 unless they are fortified.

You can get the recommended amounts of vitamin B12 by eating a variety of the foods including:

  • Organ meats (beef liver)
  • Shellfish (clams)
  • Meat, poultry, eggs, milk and other dairy foods
  • Some breakfast cereals and nutritional yeasts

To find out if vitamin B12 has been added to a food product, check the nutrition fact panel on the food label.

The body absorbs animal sources of vitamin B12 much better than plant sources. Non-animal sources of vitamin B12 vary in their amount of B12. They are not thought to be reliable sources of the vitamin.

Side Effects

A lack of vitamin B12 (B12 deficiency) occurs when the body does not get or is unable to absorb the amount of vitamin that the body needs.

  • Many people over age 50 lose the ability to absorb vitamin B12 from foods.
  • People who follow a vegetarian or vegan diet should try to eat vitamin B12-fortified foods or talk to their health care provider about taking B12 supplements.
  • People who have had gastrointestinal surgery, such as weight loss surgery, lose the ability to absorb vitamin B12.
  • People who have digestive disorders, such as celiac disease or Crohn disease, may not absorb enough vitamin B12.

Low levels of B12 can cause:

  • Anemia and pernicious anemia
  • Loss of balance
  • Numbness or tingling in the arms and legs
  • Weakness