Cysteine is an all-purpose amino acid. It is synthesized internally from methionine but requires Vitamin B-6 for the conversion to take place. It helps to break down harmful toxins, thereby protecting and preserving the cells. An effective free radical destroyer, it protects the liver and brain from damage caused by alcohol and cigarette smoke. In its antioxidant role, cysteine works best when taken with the antioxidants selenium and Vitamin E. Along with selenium, it is an important cofactor in the formation of glutathione peroxidase, one of the most powerful antioxidants. Without proper levels of cysteine, the body is not able to produce the amino acid glutathione, a powerful antioxidant in its own right. Its chelating effect enables it to remove excess copper from the body. This amino acid also promotes the burning of fat and the building of muscle.
Due to its effectiveness in breaking down respiratory mucus, this amino acid has been used to treat bronchitis, emphysema, and tuberculosis. Because the hair and skin are composed of 10-14% cysteine, it is also helpful for the healing of burns and recovery of post-operative wounds. This amino acid is believed to prevent wrinkles as well.
Cysteine is very unstable and is easily converted to the amino acid cystine, the stable form of this sulfur-rich amino acid. In metabolic terms, they may be thought of as the same. Because of its instability and potential toxicity, it is recommended that cysteine supplements be taken with large doses of Vitamin C to prevent it from increasing the risk of forming kidney stones, but Vitamin C is not required to convert to cystine.
Diabetics should seek a doctors approval before taking cysteine supplements because insulin contains large quantities of the amino acid, and because it is a vital component of the glucose tolerance factor. Cysteine levels often fall with advancing age, and supplements may be taken to boost blood levels of the amino acid. Cysteine supplementation is recommended for treating rheumatoid arthritis.