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How can one supplement offer so many potential benefits? Why aren’t more people taking this stuff? These are just a few of the questions I couldn’t stop asking myself as I revisited the interesting roles N-acetyl cysteine plays in our overall health.

What Is N-Acetyl Cysteine?

N-acetyl cysteine (or NAC for short) is a precursor to the sulfur-rich amino acid L-cysteine.

L-cysteine is found naturally in many protein– and sulfur-rich foods, including meat, poultry, egg yolks, broccoli, Brussels sprouts, garlic, oats, onions, and red bell peppers.

L-cysteine is classified as a “conditionally essential” amino acid, which means that under certain conditions, we need to consume extra sources because our body cannot make adequate amounts of it from other amino acids.

NAC is not an essential nutrient and it’s not found in nature, so there isn’t an established daily requirement for N-acetyl cysteine.

NAC may be most familiar to physicians since it’s used as a standard treatment for acetaminophen toxicity (overdose of the active ingredient in Tylenol®). NAC is also used medically as an aerosolized mist to break up mucus in the airways of patients with cystic fibrosis.

It’s also a common dietary supplement ingredient that has more functions than simply being a protein building block. Let’s explore.

What are the Potential Health Benefits of NAC?

Enhances Antioxidant Capacity

N-acetyl cysteine acts on its own as an antioxidant and is also used for the formation of glutathione. The amino acids cysteine, glycine, and glutamic acid combine to form glutathione, the body’s primary antioxidant.

Low glutathione levels can lead to premature aging, excessive free radical production, and difficulty with Phase I detoxification.

Cysteine is the rate-limiting amino acid, meaning if you don’t consume enough of it, you can’t produce enough glutathione.

The liver, lungs, and kidneys produce the most glutathione. Glutathione is built inside our cells with the three amino acids mentioned above. It cannot get transferred from the outside of the cell to inside of it, so supplementing with glutathione itself doesn’t seem to work well. Instead, you’re better off taking NAC to support glutathione capacity.

Promotes Respiratory Health

Multiple research studies show NAC has a positive impact on respiratory health. It’s often recommended as a mucolytic agent, meaning it helps break down mucus in our airways for both acute and chronic conditions that affect breathing.

Both a systematic review and a meta-analysis of clinical trials suggest NAC may be particularly helpful for reducing the frequency and duration of bronchitis symptoms in those with chronic, recurring bronchitis.

Evidence also suggests regular use of NAC seems to improve lung function in those with chronic obstructive pulmonary disease (COPD).

NAC may also help with other inflammation-related breathing conditions, such as asthma and nasal sinus infection; it’s even been shown to have protective effects in smokers.

Supports Immune Health

In one well-designed study of elderly subjects, 600 mg of NAC taken twice daily appeared to significantly reduce symptoms of viral respiratory illnesses (influenza), even though it did not reduce the risk of becoming infected.

However, another interesting study did show that a combination of NAC and L-theanine significantly reduced the incidence of the common cold and fevers, though it had no apparent effect on the duration of the cold.

A meta-analysis of NAC’s effects during acute respiratory distress syndrome (ARDS), which often requires risky and costly hospital management in intensive care units (ICUs), found that patients treated with NAC had shorter ICU stays than those not given the supplement. Interestingly, the short term and 30-day mortality were not different between the two groups, but the duration of ICU stays were significantly shorter in the NAC group.

While NAC may not be a “magic bullet,” it may help reduce the demand for critical care.

Encouraging results like these show the need for further research on dietary supplements and immune health.

Helps Cognitive, Neurological, and Behavioral Health

Perhaps related to NAC’s antioxidant function, it appears to mitigate cognitive disturbance of neuroinflammation in healthy subjects and those with other neurological disorders (including trauma, Alzheimer’s disease, Parkinson’s disease, and drug use).

Although the specific mechanisms behind NAC’s cognitive benefits are not well understood, it appears to be helpful as an individual supplement and in combination with other antioxidants, such as alpha-lipoic acid, vitamin A, vitamin E, and omega-3s.

Some research shows NAC supplementation reduces compulsive behavior, such as hair pulling, skin picking, and other obsessive-compulsive behaviors. It also shows promise as a treatment for substance abuse and withdrawal in those with cocaine addiction.

A meta-analysis of several clinical studies concluded that NAC helps reduce depressive symptoms and improve overall cognitive function and was well tolerated.

Supports Cardiovascular Function

Dietary cysteine intake appears to be inversely associated with ischemic stroke in women, meaning women with higher dietary cysteine intakes tend to have fewer strokes.

Supplemental NAC has been studied as a potential treatment option for several cardiovascular disease conditions, in addition to existing standard treatments, for its role in helping support nitric oxide production and endothelial function. One study of patients in end-stage renal failure showed 600 mg of NAC twice daily reduced heart attack or stroke as compared to a placebo. 

Improves Inflammatory Response

Researchers gave NAC in doses of 1,200 mg per day, 600 mg per day, or a placebo to three different groups of patients who all had COPD and elevated C-reactive protein (one of the most common measures of systemic inflammation).

After 10 days, 90 percent of those who took 1,200 mg per day, 52 percent of those who took 600 mg, and 19 percent of the placebo group saw their C-reactive protein levels return to normal. 

In another study, the use of 1.8 grams of NAC per day lowered homocysteine levels — another marker of systemic inflammation — by 11.7 percent. Elevated homocysteine, like C-reactive protein, is considered a risk factor for cardiovascular disease.

Promotes Liver Health and Detoxification

The liver is our primary detoxification organ, and it relies heavily on adequate glutathione antioxidant capacity to protect itself from the potentially harmful effects of unstable compounds that are either ingested or produced by the body.

NAC is one of several compounds known to promote the activity of certain Phase I detoxification enzymes our liver relies on to neutralize and filter out waste products or toxins from circulation.

It’s also been shown to help reduce the negative effects of non-alcoholic fatty liver disease, or NAFLD, the most common chronic liver disease in the United States that affects as many as one in three adults.

Other Potential Benefits

NAC appears to help improve insulin sensitivity in women with polycystic ovary syndrome (PCOS), but it’s not yet clear if NAC helps other populations with insulin resistance. As such, it’s not a replacement for other treatments or medications for diabetes. Interestingly, NAC is also being studied as a possible treatment to help improve fertility rates in women with PCOS, too.

A newly published study of patients with multiple sclerosis (MS) showed NAC improved cerebral glucose metabolism, which translated to improved cognitive function.

NAC may also help reduce muscle fatigue and improve force output, especially in those with low glutathione levels. Early studies suggest improvements can be significant with as little as 30 days of supplementation.

These are promising areas of investigation since MS is thought to be a progressively-worsening condition that leads to neurocognitive and physical function declines.

Beyond NAC’s apparent roles supporting optimal physiologic function, other evidence suggests NAC supplementation may slow visual signs of aging through improved antioxidant capacity, glutathione support, and decreased DNA damage in the skin.

How Much NAC Is Effective?

The typical dose for supporting skin health is 200 to 400 mg per day, though doses for other benefits range from 45 to 2,400 mg per day.

Most therapeutic applications call for 600 to 900 mg twice per day.

Cautions With NAC Supplementation

Though the short-term benefits of N-acetyl cysteine are significant, some theorize it may not be a great supplement for long-term use by healthy and fit individuals.

It turns out that curbing inflammation too much or overdoing antioxidants can work against you.

One small study of 10 men who took 20 mg/kg per day of NAC for eight days (that’s just over 1,500 mg a day for a 170-pound person) showed that while their antioxidant status improved and inflammation decreased, they also experienced a mild slow down of muscle recovery.

This is in line with what happens with NSAIDs, such as ibuprofen, as well. The decrease in inflammation from their use slows muscle recovery and growth.

If you’re fit and healthy, it’s probably best to use NAC for short periods, when you need to support your respiratory health or detoxification, as opposed to using it daily.

NAC is contraindicated during certain cancer treatments and if someone is taking blood thinners or nitroglycerin as well.

As with any supplements, it’s best to check with your doctor before making significant changes to your supplement routine, especially if you take any prescription medications or are managing any health conditions.

Bottom Line

Although N-acetyl cysteine isn’t an essential nutrient with an established recommended dietary intake, evidence suggests it may serve several health-promoting roles, especially if your diet is lacking in quality protein or sulfur-rich vegetables.

Learn more about our favorite N-acetyl-cysteine supplement, Thorne NAC here.

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paul-kriegler-registered-dietician-life-time
Paul Kriegler, RD, CPT

Paul Kriegler, RD, LD, CPT, CISSN, is the program developer for nutritional products at Life Time. He’s also a USA track and field coach.

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