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Short for N-acetyl cysteine, NAC is the supplement form of cysteine, an amino acid found in protein-rich foods such as beef, turkey, eggs, fish, and nuts. Because your body can produce it from the amino acids methionine and serine—also found in high-protein foods—it’s classified as a non-essential or conditionally essential amino acid.
Cysteine is necessary for the production of glutathione, one of the body’s most important antioxidants. Called the “master antioxidant,” glutathione protects against free radical damage to cells and plays a critical role in immunity, healthy aging, and disease prevention.
By promoting glutathione production, NAC supports immune health, and supplementing with NAC has been shown to enhance the activity and function of immune system cells, to inhibit replication of the influenza A virus, and to significantly reduce flu-like episodes and symptoms. Now, some researchers suggest that NAC may have potentially powerful actions in preventing or treating Covid-19.
But NAC offers benefits beyond immunity. Some highlights:
1. Lung and respiratory function.
By protecting against cellular damage, reducing inflammation in the lungs, and thinning mucus secretions, NAC can promote healthy breathing and respiratory function. Findings are mixed, but some research suggests that NAC can improve lung function, reduce wheezing and coughing, and benefit respiratory conditions such as chronic obstructive pulmonary disease (COPD) and bronchitis.
2. Brain health.
By enhancing glutathione levels and reducing oxidative damage, NAC can promote brain health and cognitive function. Some human trials link NAC with improved brain function, and other research suggests that it can protect against neurodegeneration, slow the loss of cognitive function, prevent memory decline, and lessen the risk of Alzheimer’s disease and other forms of cognitive impairment.
3. Psychiatric disorders and addictions.
NAC can benefit certain psychiatric conditions thought to be related to oxidative stress, including bipolar disorder and schizophrenia. And it shows promise in treating obsessive-compulsive disorder (OCD) and depression. NAC may also play a role in substance abuse and addictions, and studies suggest that it can decrease cravings, reduce withdrawal symptoms, and lessen the chance of relapse.
4. Detox and liver support.
Cysteine helps the body deal with environmental toxins and chemicals—in hospital settings, intravenous NAC is used to reduce liver and kidney damage after paracetamol (acetaminophen) overdose. Some research suggests that NAC supplementation can reduce inflammation, protect against free radical damage, and improve liver function in people with some forms of liver disease.
5. Healthy aging.
The body’s levels of glutathione naturally decrease with age, so by boosting glutathione, NAC may mitigate this decline. In one recent study, subjects who took a combination of NAC and glycine—also needed for glutathione production—showed improvements in many characteristic effects of aging, including inflammation, insulin resistance, body fat, and cognitive function. Other research suggests that NAC can inhibit cancer cell growth, reduce markers associated with cardiovascular disease, diminish the effects of aging, and promote longevity.
Most people can make enough cysteine through dietary sources, but low protein intake is linked with decreased levels of cysteine and glutathione, so vegans and vegetarians may be lacking. Plus, your body needs other nutrients, including folate, vitamin B6, and vitamin B12—found primarily in animal proteins—to synthesize cysteine. If any of these are in short supply, supplementing with NAC can fill in the gaps.
Despite the recent FDA warning letter to supplement manufacturers, NAC is still available over-the-counter—for now. Look for a high-quality capsule, tablet, or softgel that is free from additives or fillers. Most are sold in 500 or 600 mg formulations. In general, the recommended dosage is 500–600 mg, once or twice a day, preferably on an empty stomach to enhance absorption.
When Should I Take NAC?
Like other amino acid supplements, NAC should be taken either 30 minutes before or two hours after eating to avoid competing with protein for absorption.