Cysteine belongs to the sulphur group of amino acids. It is obtained from dietary sources and can also be synthesized from methionine. Cysteine contributes to the structure of proteins, in the form of cystine. (Cystine is created when two molecules of cysteine bond together the two amino acids can for most purpose be considered as the same). It also plays a role in energy metabolism and can be converted to glucose if necessary. Cysteine supply may be a limiting factor for white blood cell (lymphocyte) function. Research has shown that cysteine supply is impaired in a number of conditions associated with immunodeficiency, including Aids.
In the liver, cysteine is used to form the amino acid glutathione which helps to detoxify potentially harmful substances and free radicals. It is also a precursor of the detoxifying amino acid taurine.
A cysteine deficiency can result in allergic-like chemical sensitivities and in abnormal glucose metabolism, since cysteine is involved in glucose metabolism and holds the insulin molecule together.
Do not supplement cysteine or glutathione in insulin-dependent diabetes because cysteine acts as a coenzyme for insulin degeneration.
Vegetarian sources: Weight for weight, soya protein concentrates, almonds, sesame seeds and walnuts are as rich in cysteine as animal proteins.
Availability of supplements: N-acetyl cysteine is becoming the preferred form of cysteine supplementation, and is available in health food shops or through practitioners. As a detoxification aid, the suggested dose is about 1 gram per day.