Cysteine is an amino acid—one of the building blocks of proteins—that can be manufactured within the body but can also be found in a variety of foods, including eggs. Cysteine plays an essential physiological role as a precursor compound for substances that support the immune and respiratory systems and that may help decrease the risk of cancer. Because of the significant amount of cysteine that eggs provide, they are thought to be useful as both a health enhancer and as a hair strengthener.
The World's Healthiest Foods website describes cysteine as an amino acid that contains sulfur and that can be produced by the body in a metabolic pathway involving the conversion of methionine to S-adenosyl methionine, then to homocysteine, a compound which reacts with serine to yield cysteine. Because cysteine does not need to be consumed for the body to obtain it, it is considered a nonessential amino acid.
Cysteine's main functions in the body are linked to glutathione, a compound that cysteine is a major component of and that is a vital part of the proper functioning of the immune system. Glutathione cannot be manufactured in the body without cysteine. Glutathione is an antioxidant—a chemical substance in the body that neutralizes free radicals, the compounds thought to cause damage to cells and their DNA. The presence of antioxidants like glutathione are believed to decrease the risk of serious medical problems like cancer and heart disease. According to the World's Healthiest Foods, glutathione helps the liver detoxify the bloodstream by binding to heavy metals like mercury and lead and allowing them to be eliminated from the body. In addition, cysteine by itself aids the respiratory system; it can promote the breakdown of mucus and helps decrease the symptoms of bronchitis and other respiratory ailments that cause excessive mucus development. Naturopathy Digest reports that cysteine strengthens the lining of the digestive system, stimulates immune system function by improving communication between immune cells and can be converted to glucose when metabolic fuel is needed.
Cysteine in Eggs
According to the Nutriteam.com, eggs—and, in particular, egg yolks—contain 250 mg of cysteine. The World's Healthiest Foods reports that the National Academy of Sciences recommend that men consume anywhere between 425 and 700 mg of cysteine per day, women between 425 and 575 mg of cysteine daily and children up to the age of 8 between 163 to 238 mg. Consuming eggs regularly can easily help fill these daily recommended intakes of cysteine.
According to Hair2Stay.co.uk, eggs are an important part of a diet that supports the proper growth and health of hair; the site reports that the cysteine contained in eggs is one major reason for the beneficial effects eggs have on hair strength and appearance. NaturalHairLossRemedies.com advises that cysteine improves hair texture and is thought to prevent hair loss. For healthy hair, make eggs a part of your diet at least three times a week.
Other Cysteine Sources
Other than eggs and egg yolks, cysteine is found in significant amounts in the following food sources: broccoli, cheese, poultry, wheat germ, red meat, Brussels sprouts, oats, yogurt, onions, garlic and red peppers. Two types of cysteine supplements are also available: L-cysteine hydrochloride and n-acetyl-cysteine, or NAC. The NAC form of cysteine is considered the most easily absorbable form of cysteine supplement.