What can high-cysteine foods do for you?

What events can indicate a need for more high-cysteine foods?

Food sources of cysteine include poultry, yogurt, egg yolks, red peppers, garlic, onions, broccoli, Brussel sprouts, oats, and wheat germ.


What is cysteine?

Cysteine is a sulfur-containing amino acid that occurs naturally in foods and can also be manufactured by the body from the amino acid methionine. In the production of cysteine, methionine is converted to S-adenosyl methionine (SAM), which is then converted to homocysteine. Homocysteine then reacts with serine to form cysteine. Cysteine is also found in the body and in food as cystine, an amino acid that contains two cysteines joined together.

How it Functions

What is the function of cysteine?

Promoting Antioxidant Activity

As a key constituent of glutathione, cysteine has many important physiological functions. Glutathione, formed from cysteine, glutamic acid, and glycine, is found in all human tissues, with the highest concentrations found in the liver and eyes. Glutathione is a potent antioxidant, protecting fatty tissues from the damaging effects of free radicals. The antioxidant activity of glutathione is attributed specifically to the presence of cysteine in the compound.


Glutathione also plays a vital role in the detoxification of harmful substances by the liver and can chelate (attach to) heavy metals such as lead, mercury, and cadmium. It is also believed that glutathione carries nutrients to lymphocytes and phagocytes, important immune system cells.

Help Eliminate Mucous

Cysteine also has the ability to breakdown proteins found in mucous that settles in the lungs. As a result, this amino acid may be useful in the treatment of bronchitis and other respiratory problems.

Deficiency Symptoms

What are deficiency symptoms for cysteine?

Cysteine deficiency is relatively uncommon, but may be seen in vegetarians with low intake of the plant foods containing methionine and cysteine. There is no known medical condition directly caused by cysteine deficiency, but low cysteine levels may reduce one's ability to prevent free radical damage and may result in impaired function of the immune system.

Toxicity Symptoms

What are toxicity symptoms for cysteine?

Consumption of foods containing cysteine, or its precursor methionine, is not likely to cause toxicity symptoms. However, cysteine is a brain excitoxin that can cause damage to brain cells in susceptible individuals. Such individuals do not metabolize the amino acid correctly, and, as a result, may be at risk for certain neurodegenerative diseases, including multiple sclerosis, amylotrophic lateral sclerosis (Lou Gehrig's disease) and Alzheimer's disease.

High doses of oral N-acetyl-cysteine, such as those given to patients with acetaminophen (Tylenol) toxicity, can cause nausea, vomiting, and diarrhea. Intravenous administration of N-acetyl cysteine can cause allergic reactions in a small percentage of people, characterized by skin flushing, a drop in blood pressure, irregular heart beat, and respiratory distress. Accidental overdose of intravenous N-acetyl-cysteine has proven to be fatal.

Impact of Cooking, Storage and Processing

How do cooking, storage, or processing affect cysteine?

There is no research available about the impact of cooking, storage or processing on cysteine.

Factors that Affect Function

What factors might contribute to a deficiency of cysteine?

The production of cysteine involves several nutrients. As a result, dietary deficiency of methionine, vitamin B6, vitamin B12, s-adenosyl methionine (SAMe) and folic acid may decrease the production of cysteine.

Drug-Nutrient Interactions

What medications affect cysteine?

Nutrient Interactions

How do other nutrients interact with cysteine?

There is no research available about how other nutrients interact with cysteine.

Health Conditions

What health conditions require special emphasis on cysteine?

Cysteine may play a role in the prevention and/or treatment of the following medical conditions:

Form in Dietary Supplements

What forms of cysteine are found in dietary supplements?

Many people take supplemental cysteine as a way to increase the level of glutathione in the body. As a dietary supplement, cysteine is available as L-cysteine hydrochloride, and more commonly as n-acetyl-cysteine (NAC). NAC is a more water-soluble form of cysteine, and as such is believed to be more bioavailable than oral L-cysteine hydrochloride.

Food Sources

Food Source Analysis not Available for this Nutrient

Public Health Recommendations

What are current public health recommendations for cysteine?

In its most recent 2005 public health recommendations for amino acids (published as the Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients), National Academies Press, 2005), the National Academy of Sciences (NAS) established a general principle for cysteine intake. The NAS lumped cysteine together with another sulfur-containing amino acid, methionine, and recommended that all individuals 1 year of age or greater consume 25 milligrams of cysteine plus methione (combined) for every 1 gram of food protein. Here is how that recommendation would look for each age and gender group, assuming RDA-level protein intake and 50% of sulfur-containing amino acid needs supplied by cysteine:


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