What is L-cysteine?

L-cysteine, also abbreviated as C or Cys, is a naturally occurring α-amino acid containing sulphur. Sulphur is a very important element vital for normal, healthy growth and metabolism. Since L-cysteine can be synthesised in the human liver it is not classified as an ‘essential’ amino acid. However, in order to meet our daily body’s requirement for L-cysteine it’s important to supplement this amino acid through our diet. The concentration of L-cysteine in protein is very small (approximately 2%), so a varied diet is needed to counteract this shortage.

L-cysteine is produced from an essential amino acid called methionine. Methionine and cysteine are involved in many vital catalytic reactions that keep our body functioning properly. Again, our diet plays a critical role in how much of this essential amino acid is available to our body. As we are unable to produce our own methionine, we must rely on the foods we eat to maintain a healthy supply. Having a sufficient quantity of methionine available is critical for our body to produce L-cysteine.

L-cysteine has many significant roles within our body. It counteracts copper toxicity and protects against the harmful effects of tobacco and alcohol use. Cysteine also helps with the detoxification and the protection of cells from free radicals.

Additionally, due to the sulphurous content, L-cysteine has important antioxidant properties. In combination with glycine and glutamic acid, L-cysteine contributes to the formation of one of the most powerful antioxidants in the human body, glutathione. Glutathione, amongst other functions, is responsible for maintaining antioxidants such as vitamins C and E in their active form. This is very important for helping protect our body from harmful toxins.

Given the critical functions cysteine plays within our body it’s important to supplement our own production through our diet. This will ensure that our cysteine levels remain adequate. Protein rich foods are the best source of L-cysteine. Eating a varied diet of foods such as dairy and meat, as well as vegetables such as broccoli, garlic and onion, will help to boost L-cysteine levels.

To meet the daily needs of about 1,400 mg L-cysteine a diet including meat and soy products is usually recommended. Pork and chicken are particularly good sources, providing approximately 220 to 240 mg per 100 g and can help increase L-cysteine levels. Also, raw salmon (about 219 mg per 100 g) and chicken eggs (about 272 mg per 100 g) are suitable for an adequate intake of L-cysteine. Vegetarians may include sunflower seeds (about 451 mg per 100 g) and walnuts (about 208 mg per 100 g) as their sources, soybeans especially have a very high content (about 655 mg per 100 g).

It’s important to understand that L-cysteine is highly soluble in water. This means that you need to keep this in mind during food preparation. If foods containing L-cysteine are exposed to long periods in water the amino acid will be leached out and you won’t receive the full benefits.

For people who struggle to get enough L-cysteine rich foods in their diet or need a boost of this amino acid there are a variety of dietary supplements available.
Generally people suffering from health issues such as chronic diseases, cataracts and arthritis have a larger requirement for semi-essential amino acids. These patients may considerably benefit from an appropriate supplement.

Also, digestive diseases increase the demand for L-cysteine. Disorders of the gastrointestinal tract reduce the absorption capacity and thus valuable nutrients are lost and cannot be recycled.

Furthermore, environmental factors such as stress or a high physical exertion place a larger demand on cysteine than usual. People who engage in low protein diets also run the risk of significantly reducing the body’s reserves of vitamins and amino acids.

Functions of L-cysteine

Your physical well-being is strongly tied to cysteine as this amino acid offers a wide range of advantages.

L-cysteine has powerful anti-aging properties and the ability to help protect us from a wide range of serious diseases. It is involved in the formation of essential fatty acids, and thus allows the production of cell membranes and nerve sheaths. This vital amino acid plays an important role in the protection of myelin and neurons from environmental damage, helping to keep the brain healthy and discouraging degenerative diseases like Parkinson’s.

L-cysteine plays a significant role in the disposal of hazardous and/or toxic substances from the body because it can support the synthesis of the antioxidant glutathione. It can also be stored in this form which is important because free L-cysteine is very unstable. Glutathione helps to protect numerous tissues and organs throughout the body. It can also guard against Alzheimer’s disease and Multiple Sclerosis, as these diseases are associated with an accumulation of toxic substances.

Glutathione also inhibits inflammatory reactions and leads to an increased production of immune cells. At the same time it stimulates the production of leukotrienes, which support the work of the white blood cells and act as chemical messengers. This helps to maintain vitality and reduce illnesses.

A cysteine deficiency can lead to an increase in infections and inflammatory responses, which are accompanied by a strong decrease in the number of natural defence cells. In the worst case scenario, such a deficiency can contribute to developing life-threatening diseases such as cancer.

Cysteine is required for the formation of many structural proteins of the connective tissues. This means that the health of your skin and hair is partly dependant on this amino acid. It helps to add strength to tissues and it also produces taurine. Taurine is an important organic acid used in the transmission of nerve impulses, as well as being essential for the digestive tract and the cardiovascular system.

Various studies have investigated the influence of regular L-cysteine doses in the development of inflammatory reactions. It has been well established within scientific research that there is a direct link between oxidative stress and inflammatory processes. It has been hypothesised that the elimination of harmful free radicals will help to reduce the risk of inflammation of existing diseases. Ultimately, this research discovered that L-cysteine supplementation helps to reduce inflammation and assists in promoting faster healing without any negative side-effects.

Studies have shown that L-cysteine can play an important role in controlling Osteoporosis. This debilitating disease leads to an increase risk of bone fractures and a reduction of bone density. It has been found that low bone densities are often closely associated with a low plasma concentration of cysteine.

Higher doses of L-cysteine may reduce bone loss significantly. This amino acid helps to combat Osteoporosis two ways. Firstly, it reduces the activity of osteoclasts. These are bone cells that eliminate bone tissue by breaking down the organic structure. Simultaneously, L-cysteine can increases collagen synthesis that is normally reduced as a result of Osteoporosis.


L-cysteine is a vital amino acid that is widely utilised within the body. Its sulphur content helps to covert toxic heavy metal compounds into stable complexes that can be removed from the body. In carrying out its natural functions alongside other amino acids, cysteine offers excellent anti-oxidant effects and can help to boost the immune system and fight off infections.

Not only that, because cysteine protects the cells of the nervous system from oxidative degradation it helps to prevent debilitating diseases like Alzheimer’s and Parkinson’s.

While L-cysteine improves your inner health its strong anti-aging properties are also very desirable. Cysteine contributes to a healthy appearance through strengthen and stabilising human connective tissue, providing you with healthy hair and skin.

Since L-cysteine has many positive effects on human health, it’s important not only for the prevention of diseases, but also for therapeutic purposes such as the treatment of Osteoporosis. Undoubtedly as more research is conducted on this amazing amino acid further revelations of its health benefits will be revealed.

Next time you are thinking about your diet, remember to try and include L-cysteine rich foods or appropriate supplements to enhance your well-being and longevity.