   Vitamin B12 is an essential water-soluble vitamin that is
commonly found in a variety of foods, such as fish, shellfish,
meat, eggs, and dairy products. Vitamin B12 is frequently used
in combination with other B vitamins in a vitamin B complex
formulation. Vitamin B12 is important in DNA synthesis. Vitamin
B12 is bound to the protein in food. Acid in the stomach
releases B12 from protein during digestion. Once released, B12
combines with a substance called intrinsic factor (IF) before it
is absorbed into the bloodstream.  The human body stores several
years' worth of vitamin B12 in the liver, so low levels in the
body are rare. Decreases in vitamin B12 levels are more common
in the elderly, HIV-infected persons, and vegetarians. Inability
to absorb vitamin B12 from the intestinal tract can cause a type
of anemia called pernicious anemia. Fever and symptoms of
"excessive sweating" have been reported with anemia due to low
levels of vitamin B12; however, these are fixed with vitamin B12
treatment.