What is Cysteine?

Cysteine is a sulfur-containing non-essential amino acid commonly found in high-protein meat products. It is synthesized by the body if there is a substantial amount of methionine, another non-essential amino acid, available. It has a chemical structure similar to that of selenocysteine, with the difference being that selenocysteine contains a selenium atom instead of a sulfur atom.

As a nutritional supplement, this substance reportedly has several benefits. When consumed, it is converted into glutathione, an antioxidant. Antioxidants have been reported to have numerous health benefits for humans, including the reduction of free radical damage. Scientists believe that free radicals damage the deoxyribonucleic acid (DNA) and membranes of cells, which can lead to premature aging, heart disease and cancer. It can be converted into a powerful antioxidant that can prevent this damage, which might lower a person's risk for heart disease and certain types of cancers.

When given intravenously, cysteine also might prevent or reduce liver or kidney damage caused by an acetaminophen overdose. It also might reduce the symptoms of influenza, acute respiratory distress syndrome (ARDS), asthma, cystic fibrosis, emphysema and Sjogren's syndrome. It also has a preventative effect against colon cancer and cataracts. People recovering from cocaine addiction, severe schizophrenia episodes or gambling addiction also might benefit from taking it. It also can help women with polycystic ovary disease become pregnant, because of its ability to improve their fertility rate.

It occurs naturally in some dietary sources, such as meat and vegetable products. High-protein foods, such as pork, sausage, chicken, turkey, eggs, whey protein and yogurt, contain a high amount of this amino acid. Some vegetables, such as Brussels sprouts, broccoli, garlic and red peppers also contain a high amount of it.

It is available in supplement form as N-acetyl-L-cysteine (NAC). When consumed, the body converts this into cysteine. The NAC form of it is specifically used to prevent side effects caused by some drugs. It also is used to break down mucus in the body and might reduce the severity of bronchitis and chronic obstructive pulmonary disease (COPD), which are worsened by mucus buildup.

This amino acid is available in spray, liquid, topical ointment, powder or capsule form. Although NAC might prevent liver and kidney damage, it can raise homocysteine levels, which can increase a person's risk for heart disease. NAC also might cause vomiting, diarrhea and nausea. Some forms of this amino acid, including D-cysteine and 5-methyl cysteine, are potentially toxic.