Cysteine is a nonessential amino acid, which means that
it is manufactured from other amino acids in the liver; it does not have to be
obtained directly through the diet. It is synthesized in the liver from
Cysteine is an important free radical antioxidant in
cellular systems. It blocks oxidants of the free radical type that may be
engaged in certain forms of cellular pathology, including aging,
carcinogenesis, diabetes mellitus, and the development of heart disease.
Cysteine is incorporated in the cellular glutathione, which works along with
vitamin E to protect cells against free radical oxidant damage.
Deficiencies of a nonessential amino acid will not occur
if a well-balanced diet is consumed because the intake of proper foods will
allow the body to produce exactly the amount of amino acid required to function
optimally. For cysteine, deficiencies of methionine, vitamin B-2, or selenium
will result in poor metabolism of cysteine and reduced antioxidant protection.
Cysteine is best administered therapeutically as
glutathione or in combination with adequate vitamin B-6, vitamin B-12, and
folic acid. Doses of cysteine are between 100 and 500 mg per day.