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L-cysteine is a protein amino acid that exists naturally as a
protein in most living organisms. Although most cysteine is found in
proteins, small amounts cysteine are also located in body fluids and
in plants in non-protein form. The average diet of most individuals
contributes approximately 1 gram of L-cysteine
daily.
L-cysteine is considered a nonessential amino acid,
meaning that sufficient amounts are formed by the body itself.
Cysteine is one of the few amino acids that contains sulfur. This
allows cysteine to bond in a special way and maintain the structure
of proteins in the body.
L-cysteine aids in the synthesis of
proteins, glutathione, taurine, coenzyme A and inorganic sulfate in
the body. Glutathionine itself has a number of biochemical
functions, including maintenance of normal cellular redox state.
Certain conditions, e.g. an acetaminophen overdose, can deplete
hepatic glutathione, and this can be life-threatening. The antidote
to an acetaminophen overdose is L-cysteine, in the delivery form of
N-acetylcysteine. The L-cysteine derived from N-acetylcysteine helps
to restore hepatic glutathione.
Medical
Indications
Cysteine can also be transformed into
glucose and used by the body as a source of energy. Cysteine
strengthens the protective lining of the stomach and intestines,
which may help prevent damage caused by aspirin and similar drugs.
Additionally, cysteine may play an important role in the
communication between immune system cells. Cysteine is rarely used
as a dietary supplement. N-acetyl cysteine (NAC), which contains
cysteine, is more commonly used as a
supplement.
Dosage and
Administration
The usual supplemental dosage of
L-cysteine is 500 milligrams to 1.5 grams daily. Those who
supplement with L-cysteine should drink at least six to eight
glasses of water daily in order to prevent cystine renal stones.
Some studies indicate that an intake of 3 to 5 grams daily of
vitamin C may prevent cystine stones. However, high-dose vitamin C
itself may contribute to renal stones in some (see Vitamin
C).
Healthy people do not need to supplement N-acetyl
cysteine. Optimal levels of supplementation remain unknown, though
much of the research uses 250-1,500 mg per
day.
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