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Cysteine and Cystine - Benefits, Deficiency Symptoms And Food Sources

What is Cysteine and Cystine ?

These two amino acids are closely related; each molecule of cystine consists of two molecules of cysteine joined together. Cysteine is very unstable and is easily converted to L-cystine; however, each form is capable of converting into the other as needed. Both are sulfur containing amino acids that aid in the formation of skin and are important in detoxification. Cysteine is present in alpha-keratin, the chief protein constituent of the fingernails, toenails, skin, and hair. Cysteine aids in the production of collagen and promotes the proper elasticity and texture of the skin. It is also found in a variety of other proteins in the body, including several of the digestive enzymes.

Cystine or the N-acetyl form of cysteine (N-acetylcysteine, or NAC) may be used in place of L-cysteine. NAC aids in preventing side effects from chemotherapy and radiation therapy. Because it increases glutathione levels in the lungs, kidneys, liver, and bone marrow, it has an anti aging effect on the body-reducing the accumulation of age spots, for example. NAC has been shown to be more effective at boosting glutathione levels than supplements of cystine or even of glutathione itself.

Uses and Benefits of Cysteine and Cystine

Cysteine helps to detoxify harmful toxins and protect the body from radiation damage. It is one of the best free radical destroyers, and works best when taken with selenium and vitamin E. Cysteine is also precursor to glutathione, a substance that detoxifies the liver by binding with potentially harmful substances there. It helps to protect the liver and brain from damage due to alcohol, drugs, and toxic compounds in cigarette smoke.

Since cysteine is more soluble than cystine, it is used more readily in the body and is usually best for treating most illnesses. This amino acid is formed from L-methionine in the body. Vitamin B6, vitamin12 and folate are necessary for cysteine synthesis, which may not take place as it should in the presence of chronic disease. Therefore, people with chronic illnesses may need higher than normal doses of cysteine, as much as 1,000 milligrams three times daily for a month at a time.

People who have diabetes should be cautious about taking supplemental cysteine because it is capable of inactivating insulin. Persons with cystinuria, a rare genetic condition that leads to the formation of cystine kidney stones, should not take cysteine.

Deficiency Symptoms of Cysteine and Cystine

In chronic diseases it appears that the formation of cysteine from methionine is prevented, resulting in a deficiency.

Recommended Dosage of Cysteine and Cystine

General dosage is not known but as supplement cysteine is used at 200 mg two to three times per day. 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.

Rich Food Sources of Cysteine and Cystine

Cysteine is available in wholegrains, soyabeans, red peppers, garlic and leafy vegetables. And bananas, broccoli, dates, meat, eggs, and milk all contain cystine.


People suffering from diabetes should be careful when taking supplementation, as it could inactivate insulin. With typical doses of 1 to 1.5 grams daily, the most commonly reported side effects have been gastrointestinal, such as nausea. There are rare reports of cystine renal stone formation.

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