Vitamin B6 is an essential water-soluble vitamin that performs a wide variety of functions in the body. It is needed for more than 100 enzymes involved in protein metabolism, as well as for red blood cell metabolism. The nervous and immune systems need vitamin B6 to function efficiently, and it is also needed for the conversion of tryptophan (an amino acid) to niacin (a vitamin). Vitamin B6 also helps support normal range blood glucose (sugar) levels. When caloric intake is low the body needs B6 to help convert stored carbohydrates to glucose. Because of its involvement in protein metabolism and cellular growth, B6 is important to the immune system. It supports the health of lymphoid organs (thymus, spleen, and lymph nodes) that produce white blood cells.