What Are B12 Shots Used For?

Vitamin B12, found primarily in animal products such as meat, poultry, fish, milk, eggs and cheese, helps to maintain nerve cells and breaks down some fatty acids and amino acids. Although the Recommended Dietary Allowance for adults is quite small, 2.4 micrograms per day, a deficiency can occur due to inadequate intake or problems in the digestive system that interfere with absorption of the vitamin. In some cases, vitamin B12 injections are prescribed to correct a deficiency.

Inadequate Intake

The daily requirement of just over two millionths of a gram seems like a tiny amount, especially when it is available in many foods and the body can store it for years. Yet if a person chooses to avoid foods that are rich in vitamin B12, inadequate intake over a prolonged period of time can result in a deficiency of the vitamin.

Inadequate Absorption

Some people, especially those over 60 years of age, develop a condition called atrophic gastritis, which damages the cells of the stomach. This condition can also result from iron deficiency or an infection from the bacteria implicated in the formation of ulcers. As a result of this condition, the production of a chemical called intrinsic factor, normally made by the stomach, diminishes and vitamin B12 absorption decreases, according to Eleanor Whitney and Sharon Rolfes in the text "Understanding Nutrition."

Pernicious Anemia

The type of vitamin B12 deficiency caused by atrophic gastritis and lack of intrinsic factor is called pernicious anemia. This blood disorder results in abnormally large and immature red blood cells. Pernicious anemia causes muscle weakness and irreversible neurological damage.

Lack of Intrinsic Factor

Without sufficient intrinsic factor, vitamin B12 is not absorbed. Lack of intrinsic factor can also result from an injury to the stomach or from a defective gene for the intrinsic factor. No matter how much vitamin B12 is consumed in food, if it does not get absorbed into the body, a deficiency develops.

Vegetarian Diet

Vegetarians avoid eating meat, but some do consume animal products such as eggs, milk and cheese, and those foods supply enough vitamin B12 to avoid creating a deficiency. Vegans not only avoid meat, but also avoid all products derived from animals, such as eggs and dairy.
For people who stop consuming animal products, it may take years to develop symptoms of vitamin B12 deficiency because the body recycles it to use over and over again. Because vitamin B12 is needed to activate folate, one symptom of vitamin B12 deficiency is the anemia of folate deficiency, which causes DNA synthesis to slow down.

Considerations

Some people advocate vitamin B12 shots for an energy boost, but most doctors and dietitians recommend getting vitamins primarily from food and only supplementing specific vitamin deficiencies that cannot be satisfactorily met by food in a particular circumstance. Another suggested use for vitamin B12 injections is for weight loss, but a registered dietitian spokesperson for the Mayo Clinic advises there is no evidence that vitamin B12 in any form enhances weight loss.