Vitamin B12 is an essential water-soluble vitamin that is commonly found in a variety of foods such as fish, shellfish, meat, and dairy products. Vitamin B12 is frequently used in combination with other B vitamins in a vitamin B complex formulation. It helps maintain healthy nerve cells and red blood cells and is also needed to make DNA, the genetic material in all cells. Vitamin B12 is bound to the protein in food. Hydrochloric 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, so nutritional deficiency of this vitamin is extremely rare. Elderly are the most at risk. However, deficiency can result from being unable to use vitamin B12. Inability to absorb vitamin B12 from the intestinal tract can be caused by a disease known as pernicious anemia. Additionally, strict vegetarians or vegans who are not taking in proper amounts of B12 are also prone to a deficiency state. A day's supply of vitamin B12 can be obtained by eating 1 chicken breast plus 1 hard-boiled egg plus 1 cup plain low-fat yogurt, or 1 cup milk plus 1 cup raisin bran.
Liver extract and desiccated (dried) liver have been marketed as iron supplements for over a century. The extract is processed cow or pig liver that may either be a freeze-dried brownish powder or a concentrated liquid that has had most of the fat and cholesterol removed. Preliminary clinical studies indicate that liver extract may be helpful in treating hepatic (liver) dysfunction. In addition, liver extract seems to work synergistically with interferon in treating hepatitis C and other viral infections. More research is needed in these areas. Laboratory studies indicate that liver extract may have some effects that could be useful in treating certain forms of cancer, such as the ability to direct migration of metastasizing cells and the inhibition of DNA, RNA, and protein formation. More research is needed in these areas to quantify liver extract's properties. Some concern has been raised about the safety of liver extract, as it is made of animal liver, which may be infected with parasites, bacteria, or prion diseases. Although there are currently no available reports of diseases such as bovine spongiform encephalitis (BSE, or "mad cow disease") being transmitted by liver extract, the U. S. Food and Drug Administration (FDA) still cautions against the use of any animal organ extract. It is not clear how the processing of liver extract affects the transmission of these organisms.