Cysteine

What is cysteine?

Cysteine is a conditionally essential amino acid, which can be produced in your body from another amino acid methionine, but infants may need to obtain additional amounts from foods to be healthy ^[1]. In foods, cysteine is incorporated into proteins.

Cysteine abbreviation (symbol): Cys

Cysteine Functions in the Human Body

Cysteine is ^[2]:

• A building block of proteins, especially of collagen in the skin and beta-keratin in hair and nails
• A glucogenic amino acid, which can be converted into glucose in your body ^[3]
• A source of sulfur
• A precursor of the amino acid cystine and the antioxidant glutathione

Cysteine Rich Foods

• ANIMAL FOODS: chicken, turkey, fish (bluefish, yellowtail, tuna, salmon), pork (ham) beef, veal, lamb, bison, crabs, mollusks, cheese ^[4]
• PLANT FOODS: nuts (butternuts, peanuts), seeds (pumpkin, sunflower), legumes (beans, soybeans, lentils) ^[4]

NOTE: Cysteine contains sulfur, so diet high in cysteine can cause sulfur smelling gas.

Cysteine as a Food Additive

L-cysteine obtained from animal foods, may be added to certain foods, like leavened breads, as a stabilizator. In the European Union it is labeled as the E-number E920.

Cysteine Supplements

Available forms of cysteine supplements:

• L-cysteine powder without prescription. L-cysteine may be obtained from human hair, duck feathers or other animal or plant proteins, produced using microbes or can be artificially synthesized.
• L-cysteine/N-acetyl cysteine combination
• L-cysteine hydrochloride as a prescribed solution for intravenous infusions in infants

Cysteine Health Benefits

There is INSUFFICIENT EVIDENCE about the effectiveness of L-cysteine supplements in the prevention or treatment of homocystinuria ^[5].

Cysteine Safety: Side Effects, Toxicity

L-cysteine hydrochloride injections can cause local reactions, such as a warm sensation, skin redness, vein inflammation and blood clotting ^[7].