Vitamin B-12 has the largest, most complex structure of any vitamin, according to the Linus Pauling Institute at Oregon State University. Through diet, you can get vitamin B-12 through eating foods such as eggs, meat and poultry, and it is available as a dietary supplement as well. Essential to many aspects of overall health, vitamin B-12 has a unique mechanism of action within the human body.
Separation
As soon as your stomach begins digesting food you have eaten that contains vitamin B-12 -- such as eggs, meat and poultry -- the first step of B-12's mechanism of action begins. Hydrochloric acid and an enzyme in your stomach called gastric protease initiate the separation of B-12 from the proteins to which it is bound so that your body can use the vitamin. If the B-12 comes from a food fortified with the vitamin, then it is free -- or already separated when it reaches your stomach -- and skips this step, reports the Office of Dietary Supplements.
Absorption
After separation, free vitamin B-12 combines with a glycoprotein secreted by the stomach called intrinsic factor. This allows B-12 to absorb through the stomach and into the small intestine, which uses calcium supplied by the pancreas to pull the B-12, mixed with intrinsic factor, into specialized receptors within the lining of the small intestine. After this is complete, B-12 can begin to play its crucial role within the body.
Effects of B-12
When vitamin B-12 enters the bloodstream in its new, bio-available form, it immediately begins to work for your body's health. The effects of vitamin B-12's mechanism of action within the human body include production of new red blood cells, maintenance of healthy neurological cells, and synthesis of DNA. According to the National Institutes of Health, B-12 is also pivotal in regulating your metabolism -- the process through which your body converts food into energy, maintains healthy tissues, regulates your body temperature and allows for healthy organ function.
Storage and Excretion
As with other water-soluble vitamins, excess vitamin B-12 is excreted through urine. However, B-12 is unique in that, unlike its water-soluble counterparts, it can be stored in the liver for years, according to the NIH. However, your body needs a steady supply of vitamin B-12 through diet or supplementation in order to avoid a deficiency of the vitamin, which can lead to feelings of weakness, numbness and potentially cause anemia. Ensuring that you're getting enough B-12 is especially important if you are a vegetarian or vegan, in which case you must talk to your physician about supplementing with B-12 to make sure you stay healthy.
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