Vitamin B-12 is one of several water-soluble B vitamins that help metabolize, or break down, food. This important vitamin also plays several other important roles. B-12 has the most complex chemical structure of all the vitamins, the Linus Pauling Institute explains. Because it is so complex, several things must be in place for it to be broken down and absorbed. Although it is a water-soluble vitamin, it is the only one that is stored in small amounts in your liver.
Purpose of Vitamin B12
Vitamin B-12 helps make new red blood cells, says the Office of Dietary Supplements. It also helps synthesize DNA, the genetic material found in all cells, and is essential for normal neurological function. If you don't have adequate amounts in your diet, you can have neurological problems, such as tingling in the limbs, confusion and loss of balance. A long-term deficiency can cause these symptoms to become permanent and irreversible. You need only 2.4 micrograms of vitamin B-12 from your diet, which you easily can ingest by consuming certain foods.
How It is Absorbed
Vitamin B-12 is bound to protein in the food you eat. When food reaches the stomach, hydrochloric acid and gastric protease release B-12. Synthetic types of B-12 in supplements and fortified foods already are in a free form and do not need to be released. Once B-12 is free, it combines with intrinsic factor, a glycoprotein secreted by the stomach. From this point it moves to the ileum in the small intestine, where it is absorbed into the bloodstream. It then travels to the liver, where it is used right away or stored for later use.
Factors Affecting Absorption
Several factors can inhibit the absorption of vitamin B-12 in your gut. As you age, you might lose glands in your stomach, a condition known as atrophic gastritis. This disorder minimizes the production of stomach acids that release B-12. Additionally, decreased stomach acid also results in an abundance of anaerobic bacteria, interfering with B-12 absorption. Pernicious anemia is an autoimmune disorder that leads to destruction of stomach cells, and also leads to decreased stomach acid and enzymes that release B-12. Lastly, having a gastrointestinal surgery in which portions of the stomach or small intestines are resectioned also can lead to malabsorption of B-12, since these organs are necessary for proper absorption.
Forms of Vitamin B-12
B-12 is a unique vitamin in that it is the only one that attaches to a mineral in order to function. It is available in many forms, but when B12 is attached to cobalt, it is referred to as methylcobalamin. Both methylcobalamin and 5-deoxyadenosylcobalamin are the types of B-12 that are most active in humans. In dietary supplements, B-12 usually is present as cyanocobalamin, which converts into usable active forms. Vitamin B-12 from fortified foods, supplements and plant foods is not easily absorbed by your body, the National Center for Biotechnology Information reports. While B-12 in these foods can be converted into methylcobalamin and 5-deoxyadenosylcobalamin, the conversion is not very efficient, limiting the amount of vitamin B-12 you absorb. Vitamin B-12 from animal foods is easier for your body to break down and absorb. Including meat, eggs, dairy, poultry and shellfish in your diet ensures that you consume adequate amounts of B-12.
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