Cysteine is a non-essential amino acid that can be manufactured in the liver. It is obtained in the diet from beans, brewer’s yeast, broccoli, Brussels sprouts, dairy products, eggs, fish, garlic, legumes, meat, nuts, onions, red peppers, seafood, seeds, soy, whey, and whole grains. N-acetyl cysteine (NAC) is a modified form of cysteine. NAC helps the body make the antioxidant enzyme glutathione.

Cysteine may help to diminish the effects of aging, protect against heart disease and cancer, boost the immune system, promotes metabolism of fats and production of muscle tissue, aid healing after surgery, promote hair growth, and prevent hair loss. It is also known to work synergistically with vitamin E and selenium as an antioxidant, protecting against the damaging effects of radiation, acetaldehyde, acrolein in tobacco smoke, alcohol and environmental pollutants.

Several studies have found that NAC is beneficial to patients with chronic bronchitis and angina; there is also preliminary evidence to suggest that it may help to prevent colon cancer Some experts believe that NAC increases the efficacy of chemotherapy drugs and helps to alleviate their side effects, however there is little clinical evidence to support this. Very high doses of NAC are given to patients in hospital to treat acetaminophen poisoning.

Symptoms of cysteine deficiency include: apathy, loss of pigmentation in hair, edema, lethargy, liver damage, muscle loss, skin lesions, weakness, fat loss, and slowed growth in children.

Optimal levels of NAC and cysteine have not been determined. 250 to 1,500 mg of NAC per day has been used in clinical studies with no adverse effects.

MAXIMUM SAFE LEVEL: Not established -there are no known signs of toxicity from cysteine. NAC appears to be a very safe supplement even in high doses, however an animal study found that 60-100 times the normal dose could cause liver injury. Note: NAC is known to have antioxidant activity, however one study found that daily doses of 1.2g or more increased oxidative stress.

People with diabetes mellitus and allergies to eggs, milk, or wheat should not take supplementary cysteine. People taking the drug may experience severe headaches when taking NAC. Cysteine supplements must be taken with vitamin C to prevent cysteine being converted to cystine, which may form kidney or bladder stones. People with kidney or liver disease should consult their doctor before taking supplementary cysteine.