What Are the Benefits of Taking an N-Acetylcysteine (NAC) Supplement?

N-acetyl-L-cysteine (NAC), often called acetylcysteine, is a modified form of the nonessential amino acid L-cysteine with strong antioxidant and mucolytic ("mucus-ridding") properties [1]. A NAC supplement also serves as an orally bioavailable source of L-cysteine, the rate-limiting amino acid of glutathione synthesis in the body.

An extensive body of evidence suggests that NAC supplements can bolster the immune system, promote lung function, and heal the liver [2]. The United States Food and Drug Administration (FDA) approved acetylcysteine as a prescription medicine in 1963, and it has been somewhat controversially marketed as a nutritional supplement in recent years. 

Read on to learn more about how N-acetyl-L-cysteine works in the body and the potential health benefits of taking a NAC supplement.

N-Acetylcysteine (NAC) and Glutathione Levels

Since L-cysteine is subject to rigorous metabolism when consumed orally, the first-pass effect degrades much of it. Therefore, taking an L-cysteine amino acid supplement is not adequate for increasing glutathione levels.

That's where N-acetylcysteine comes into play, as its structural difference makes it more resistant to metabolism. In turn, more L-cysteine distributes to tissues for increasing glutathione production and controlling oxidative stress. 

Oral N-acetylcysteine has been shown to increase glutathione levels more than supplementing with glutathione itself [3]; glutathione is a tripeptide (made up of three amino acids bonded together), so proteolytic enzymes in the intestines can separate the amino acid bonds before it gets absorbed into the blood circulation. This is the same reason taking performance-enhancing peptides, like human growth hormone, orally doesn't confer notable benefits. 

As noted earlier, glutathione is a crucial endogenous antioxidant in humans, neutralizing free radicals like reactive oxygen species. Glutathione also assists in the nitric oxide cycle, which is imperative for healthy blood pressure and vascular function.

Furthermore, glutathione is necessary for myriad metabolic reactions that affect practically every body system,  especially the nervous, immune, and gastrointestinal systems. Given this, supplementing with NAC helps maintain healthy glutathione levels in the body and supports crucial cellular functions [4].

N-Acetyl-Cysteine for Lung and Pulmonary Health

In addition to being an antioxidant, acetylcysteine is a mucolytic agent; in other words, NAC assists in breaking down mucus. Using mucolytics can help reduce sinus symptoms such as nasal congestion and labored breathing (dyspnea).

N-acetyl-cysteine splits the disulfide bond of mucins, which are glycosylated proteins that makeup mucus. In so doing, NAC makes adhesive mucus water-soluble so it can be expelled more easily. 

Clinical studies demonstrate the effectiveness of N-acetyl-cysteine in treating various pulmonary disorders, which tend to cause overexpression of mucins in the lungs [5]. Naturally, this knowledge has led researchers to believe that NAC may be useful as an adjunctive treatment for COVID-19.

N-Acetylcysteine (NAC) for Upper Respiratory Infections

Since the SARS-CoV-2 virus infects the upper respiratory tract, some people are turning to NAC supplements in hopes of treating the symptoms of COVID-19. While literature is abundant on the therapeutic and remedial properties of N-acetyl cysteine in treating seasonal allergies and other upper respiratory issues such as the flu and pneumonia, only a handful of COVID clinical trials have included NAC as a treatment [6, 7].

Nevertheless, a recent systematic review contends that a NAC supplement may be useful in alleviating the symptoms of COVID-19 and facilitating a quicker recovery, particularly in moderate-to-severe cases [8]. The drawback is that exceedingly large doses of NAC are necessary to inhibit viral replication and significantly reduce oxidative damage to the body after SARS-CoV-2 infection [9, 10].

In such instances, taking a sufficient dose of oral NAC is impractical; instead, it must be given intravenously or inhaled through a nebulizer.

Still, researchers support the use of oral n-acetylcysteine for fever and cough symptoms, with a minimum of 600 mg twice daily working up to a max dose of 1,200 mg twice daily. We should note that taking a NAC supplement will not prevent you from getting COVID-19.

Nutritional supplements like NAC, reduced L-glutathione, vitamin C, vitamin D3, and zinc are currently prospective treatments for mitigating the severity and duration of COVID symptoms. More data is desperately needed to confirm the impact of nutraceuticals as a multimodal approach to combating COVID-19.

Clinical trials are booming to keep up with the pace of the pandemic and inevitable variants that come along; hopefully, we will have a better understanding of the SARS-CoV-2 virus and COVID-19 in the not-too-distant future.