Vitamin B-12 is the most molecularly complex of all the essential vitamins. Its effects are wide-ranging and crucial to many aspects of your health. Though this vitamin is readily available in many common foods, disorders related to the absorption of B-12 sometimes lead to deficiencies. A chemical called intrinsic factor, which is secreted by cells in your stomach, aids in the absorption of this vital nutrient.
About B-12
B-12 is sometimes referred to as cobalamin, due to the presence of a cobalt ion within its molecular structure. Your body needs B-12 for nerve function, red blood cell formation, and the creation of substances such as DNA, hormones and proteins. When you consume B-12 in foods, it is bound to a protein that makes it difficult for your body to absorb. In your stomach, acids release B-12 from the protein that binds it, thus enabling the freed B-12 to bind with another gastric secretion: intrinsic factor.
About Intrinsic Factor
Intrinsic factor is a glycoprotein released by parietal cells that line the internal surface of your stomach. Without intrinsic factor, your body can only absorb about 1 percent of the B-12 you ingest. With the help of intrinsic factor, this amount increases to 56 percent of a 1 microgram dosage of B-12. However, Intrinsic factor has its limits. If you take dosages of B-12 that exceed the capacity of intrinsic factor -- between 1 and 2 micrograms -- absorption is decreased.
Conditions Affecting Intrinsic Factor
Some disorders can affect your ability to produce intrinsic factor and, consequently, your ability to absorb B-12. Pernicious anemia is an example of this type of malabsorption syndrome. If you have pernicious anemia, your body undergoes an autoimmune response that incorrectly identifies your parietal cells as a threat. Your immune system attacks and destroys these cells, thus compromising your ability to absorb B-12.
B-12 Deficiency
A deficiency in B-12 can take years to become apparent, as your body stores large amounts of B-12 in your liver. Once it does occur, however, B-12 deficiency is a serious matter. Adverse effects such as fatigue, weakness can be signs of megaloblastic anemia due to B-12 deficiency. B-12 deficiency can also cause nerve damage that affects cognitive and muscle function and can become permanent if not treated in time.
References
- Linus Pauling Institute at Oregon State University; Vitamin B-12; Jane Higdon; March 2003
- University of Maryland Medical Center; Vitamin B12; Linda Vorvick, MD; March 2009
- "American Family Physician"; Vitamin B12 Deficiency; Robert C. Oh, et al.; March 2003
- Office of Dietary Supplements: Vitamin B-12
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