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Vitamin B-12

Vitamin B-12
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Vitamin B12, also called cobalamin, is one of 8 B vitamins. All B vitamins help the body convert food (carbohydrates) into fuel (glucose), which is used to produce energy. These B vitamins, often referred to as B complex vitamins, also help the body use fats and protein. B complex vitamins are needed for healthy skin, hair, eyes, and liver. They also help the nervous system function properly.

All B vitamins are water-soluble, meaning that the body does not store them.

Vitamin B12 is an especially important vitamin for maintaining healthy nerve cells, and it helps in the production of DNA and RNA, the body's genetic material. Vitamin B12 also works closely with vitamin B9, also called folate or folic acid, to help make red blood cells and to help iron work better in the body. Folate and B12 work together to produce S-adenosylmethionine (SAMe), a compound involved in immune function and mood.

Vitamins B12, B6, and B9 work together to control blood levels of the amino acid homocysteine. High levels of homocysteine are associated with heart disease. However, researchers aren't sure whether homocysteine is a cause of heart disease or just a marker that indicates someone may have heart disease.

It’s rare for young people to be deficient in vitamin B12, but it’s not uncommon for older people to be mildly deficient. That may be because their diets are not as healthy or because they have less stomach acid, which the body needs to absorb B12. Low levels of B12 can cause a range of symptoms including fatigue, shortness of breath, diarrhea, nervousness, numbness, or tingling sensation in the fingers and toes. Severe deficiency of B12 causes nerve damage.

Others at risk for B12 deficiency include:Vegans, vegetarians who also don't eat dairy or eggs -- vitamin B12 is found only in animal products

People with problems absorbing nutrients, due to conditions such as Crohn’s disease, pancreatic disease, and people who have had weight loss surgery.

People who are infected with Helicobacter pylori, an organism in the intestines that can cause an ulcer. H. pylori damages stomach cells that make intrinsic factor, a substance the body needs to absorb 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.


Vitamin B12, like the other B vitamins, is important for 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 foods. 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 foodsSome breakfast cereals and nutritional yeastsTo 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. Nonanimal 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 doctor about taking B12 supplements.

Those 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's disease, may not absorb enough vitamin B12.

Low levels of B12 can cause:

Anemia, Loss of balance, Numbness or tingling in the arms and legs, Weakness, RecommendationsThe best way to meet your body's vitamin B12 needs is to eat a wide variety of animal products.

Supplemental vitamin B12 can be found in the following:

Almost all multivitamins. Vitamin B12 is better absorbed by the body when it is taken along with other B vitamins, such as niacin, riboflavin, vitamin B6, and magnesium.A prescription form of vitamin B12 can be given by injection or as a nasal gel.Vitamin B12 is also available in a form that dissolves under the tongue (sublingual).The Recommended Dietary Allowance (RDA) for vitamins reflects how much of each vitamin most people should receive on a daily basis. The RDA for vitamins may be used as goals for each person.

How much of each vitamin you need depends on your age and gender. Other factors, such as pregnancy and illnesses, are also important. Women who are pregnant or breast-feeding need higher amounts. Ask your health care provider which amount is best for you.

Dietary Reference Intakes for vitamin B12:
Infants (adequate intake)0 - 6 months: 0.4 micrograms per day (mcg/day)7 - 12 months: 0.5 mcg/day

Children1 - 3 years: 0.9 mcg/day4 - 8 years: 1.2 mcg/day9 - 13 years: 1.8 mcg/day

Adolescents and AdultsMales and females age 14 and older: 2.4 mcg/dayPregnant teens and women: 2.6 mcg/dayBreastfeeding teens and women: 2.8 mcg/day

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