Although it is not generated by the human body, the water-soluble vitamin C (also known as ascorbic acid) is vital to its proper operation. It is available through dietary sources, with citrus fruits being the major sources of Vitamin C. It supports protein metabolism and is essential for the bodys production of neurotransmitters, L-carnitine, collagen and vitamin E. It also aids in protein metabolism. Additionally, it is crucial for the immune systems operation as well as for the absorption of non-haem iron. The nutritional status of an individual can be determined by measuring the amounts of vitamin C in the blood.