Cysteine is a nonessential sulfur-containing amino acid. Sufficient amounts of cysteine are provided to our bodies from either the dietary essential amino acid methionine, or the nonessential amino acid serine via a transsulfuration reaction. Being an unstable organic compound, cysteine may also be derived from the amino cystine in times of need. Cysteine does not need to be obtained from dietary sources due to its relatively high bioavailability.

Cysteine is present in nearly all sources of protein, with minute amounts existing in body fluids and plants. The highest concentrations are found in alpha-keratin. [1] Alpha-keratin is a fibrous protein located throughout the body in various structural tissues. It is a principal constituent of digestive enzymes, fingernails, skin, and hair.

Because of its abundance, cysteine may be used for energy expenditure in humans. In times of elongated physical activities, cysteine is often converted into glucose. It is also of equal importance in the production of taurine; an amino acid that provides for a host of specialized processes within the human body.

N-acetyl cysteine (NAC) is the most popular modified form of cysteine to be used in dietary supplementation. In conjunction with L-cysteine, NAC has been recognized in the metabolization of various biochemicals in the body. These biochemicals include; biotin, coenzyme A, heparin, lipoid acid, and perhaps of greatest importance is the antioxidant glutathione.

Cysteine may be considered conditionally essential in preterm infants. Healthcare providers often recommend a complete amino acid supplement, containing cysteine, to be administered to this population of newborns.

Products Containing Cysteine
Name Price Rating Serving Price # of Servings Manufacturer Health Condition
Lean Body Chocolate Peanut Butter $48.95
$2.45 20 Labrada
Myoplex Deluxe $99.99
$2.78 36 EAS
Nisim $13.80
$0.00 0 Nisim Hair Loss
Pro Blend 55 $31.49
$2.42 13 Wellement
Superior Amino 2222 $17.99
$0.12 150 Optimum Nutrition
Whey Gourmet $27.95
$0.93 30 PVL
Whey Matrix $26.00
$0.37 71 ISS


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