Your body needs vitamin B-12 to produce healthy red blood cells, the vehicle for oxygen transportation throughout the body. Vitamin B-12 also plays an essential role in neurological function, metabolism and DNA synthesis. A variety of health conditions can affect the body's absorption of vitamin B-12. In some cases, the body may be able to absorb synthetic vitamin B-12 more easily than natural vitamin B-12. However, people who cannot absorb either type efficiently may require treatment with B-12 shots.
Absorption Basics
Naturally occurring vitamin B-12 in foods remains attached to protein until the body frees it using hydrochloric acid in the stomach. Synthetic vitamin B-12 in supplements and fortified foods is already free, and does not require this separation step. Both types of vitamin B-12 must attach to intrinsic factor, a glycoprotein, before they can be absorbed in the gastrointestinal tract. The body cannot absorb large amounts of vitamin B-12 at one time because of the limited capacity of intrinsic factor.
Low Hydrochloric Acid and Absorption Problems
A variety of factors can reduce the stomach's secretion of hydrochloric acid, reducing the body's ability to absorb vitamin B-12 from foods. Atrophic gastritis, gastrointestinal surgeries and long-term use of antacids, such as proton pump inhibitors and H2 receptor antagonists, can all reduce levels of hydrochloric acid in the stomach. Individuals with low levels of hydrochloric acid may not absorb sufficient amounts of vitamin B-12 from food, but they can absorb synthetic forms of the vitamin in fortified cereals and dietary supplements.
Low Intrinsic Factor and Absorption Problems
Pernicious anemia, a rare condition affecting only 2 percent of older adults, decreases the body's production of intrinsic factor. Individuals with pernicious anemia may not be able to absorb sufficient amounts of vitamin B-12 from foods or supplements, and typically require treatment with intramuscular B-12 injections. These B-12 shots bypass absorption problems. However, very high oral doses may also be able to treat pernicious anemia, suggests the National Institutes of Health.
Injections vs. Oral Supplements
Doctors typically treat existing B-12 deficiencies with intramuscular injections to bypass underlying absorption problems. However, high oral doses may also prove effective, some studies show. A 2003 study published in the journal "Clinical Therapeutics" found that 1,000 microgram oral doses of vitamin B-12 were just as effective at treating deficiencies as intramuscular injections. The less expensive oral doses were also better tolerated by patients. In 2006, the journal "Family Practice" published a review of studies comparing intramuscular injections and oral supplements. The review concluded that high oral doses were as effective as intramuscular injections in limited studies but suggested that further evidence may be needed to determine the efficacy of such treatment over the long-term.
References
- National Institutes of Health Office of Dietary Supplements: Vitamin B-12 Quick Facts
- "Family Practice"; Oral Vitamin B12 Versus Intramuscular Vitamin B12 for Vitamin B12 Deficiency; CC Butler, et al.; June 2006
- "Clinical Therapeutics"; Oral Versus Intramuscular Cobalamin Treatment in Megaloblastic Anemia; Z. Bolaman, et al.; December 2003
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