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.

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, medications, 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 is 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.

Supplementation with L-cysteine is recommended in the treatment of rheumatoid arthritis, hardening of the arteries, and mutagenic disorders such as cancer. Cysteine promotes healing after surgery and severe burns, chelates heavy metals, and binds with soluble iron, aiding in iron absorption. This amino acid also promotes the burning of fat and the building of muscle. Because of its ability to break down mucus in the respiratory tract, L-cysteine is often beneficial in the treatment of bronchitis, emphysema, and tuberculosis. It promotes healing from respiratory disorders and plays an important role in the activity of white blood cells, which fight disease.

Cystine or the N-acetyl form of cysteine (N-acetylcysteine) may be used in place of L-cysteine. N-acetylcysteine 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. N-acetylcysteine has been shown to be more effective at boosting glutathione levels than supplements of cystine or even of glutathione itself.

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.

Cysteine may improve allergy and sinusitis conditions. Cysteine keeps fingernails, toenails and hair in good condition. Cysteine alleviates psoriasis.

Where is it found ?

The body can synthesize cysteine from methionine  and other building blocks. Cysteine, the amino acid from which NAC is derived, is found in most high-protein foods.

Who is likely to be deficient ?

According to several studies, blood levels of cysteine and glutathione are low in individuals infected with HIV. Cysteine has a role in the proper function of the immune system, so a deficiency of this amino acid may either contribute to or result from immune suppression associated with HIV.

How much to take

Most people do not need to supplement cysteine. Almost nothing is known about appropriate supplemental levels, in part because almost all clinical research has been done with N-acetyl cysteine and not cysteine itself.

Side effects

No consistent adverse effects of NAC have been reported in humans. One small study found that daily amounts of 1.2 grams or more could lead to oxidative damage. Extremely large amounts of cysteine, the amino acid NAC is derived from, may be toxic to nerve cells in rats.
Adequate amounts of methionine are needed in the diet, as the precursor to cysteine, to prevent cysteine deficiency.

Caution

It is recommended that diabetics only use cysteine/cystine under medical supervision. When used alone or in combination with vitamins C and B, it can interfere with and deactivate insulin. Persons suffering the rare genetic illness cystinuria, that causes the formation of cystine kidney stones, should not supplement with the amino acid cysteine. Discontinue use if nausea, vomiting, diarrhea or stomach cramps occur, and consult with your physician or naturally oriented healer.

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