Vitamin B12 shots have erroneously been popularized over the years for boosting energy, speeding metabolism and promoting weight loss. In fact the supplementation of this vitamin will do nothing but cure a deficiency state. The injection form is necessary for those who cannot properly absorb the vitamin in food or pill form.
Deficiency From Inadequate Dietary Intake
The dietary source of vitamin B12 is animal products, including eggs and dairy products. Very small amounts are needed in the diet, and the vitamin is stored in the body for two to five years, according to the American Family Physician journal. Vegans, however, do not eat any animal products and therefore have no source of vitamin B12 in their diet. Taking a B12 pill would provide the required amounts. As long as there are no existing absorption problems there is no need for shots.
Deficiency From Inadequate Stomach Acid
An acid environment is required in the stomach to free vitamin B12 from food to bind with a compound called intrinsic factor (IF). It is this IF-B12 complex that is absorbed further down the digestive tract. The stomach environment typically is acidic, but when acid secretion is reduced, as may result from antacids or other medications, the vitamin will not be freed to join with IF. People also tend to produce less stomach acid with advancing age, and the Micronutrient Information Center at Oregon State University reports an estimated 10 to 15 percent of adults over age 60 suffer from a B12 deficiency. Reduced stomach acid prevents B12 from becoming available from food, but free B12 in dietary supplements is absorbable. Therefore the person with inadequate stomach acid can use oral supplements of B12 instead of injections.
Deficiency From Lack of Intrinsic Factor
If IF is not present, only about one percent of the vitamin can be absorbed. The Merck Manual reports the free vitamin will simply be excreted. The absence of intrinsic factor may occur after surgeries where part or all of the stomach is removed. Such an operation may be performed for gastric cancer, large ulcers or even weight loss surgery. Injections of B12 are generally given monthly when IF is lacking. However, oral supplementation given in megadose levels of 1000 mcg daily will allow 10 mcg to be absorbed. This is adequate to meet the recommended dietary allowance of 2.4 mcg for adults.
Deficiency From Diseases Affecting the Terminal Ileum
The last part of the small intestine, the terminal ileum, is where the IF-B12 is absorbed. Conditions preventing absorption include inflammatory bowel diseases, bacterial overgrowth, surgical removal of this portion of the small intestine or infestation with tapeworms. Injections of B12 are needed monthly to prevent deficiency in cases of intestinal malabsorption.
Treating Existing Deficiency
According to the Merck Manual, a deficiency treatment regimen consists of high-dose vitamin B12 supplements orally unless there are symptoms present. Those with symptoms are given injections daily or weekly until the blood level returns to normal. Injections are continued monthly unless the cause of the disorder can be corrected.
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