I wrote about a study indicating that NAC is beneficial in Parkinson's here: healthunlocked.com/parkinso... That benefit may have been due to NAC administered by the IV route.
The idea that NAC may mitigate coronavirus severity is based upon the effect of NAC upon influenza. From an article entitled: "Nutraceuticals have potential for boosting the type 1 interferon response to RNA viruses including influenza and coronavirus": sciencedirect.com/science/a...
"Glutathione production can also be promoted by administration of N-acetylcysteine (NAC), which has been shown to be protective in rodents infected with influenza.16., 17., 18. In a little-noticed 6-month controlled clinical study enrolling 262 primarily elderly subjects, those receiving 600 mg NAC twice daily, as opposed to those receiving placebo, experienced significantly fewer influenza-like episodes and days of bed confinement.19 Although the rate of seroconversion to influenza A was comparable in the two groups – indicating that they were exposed at the same frequency – only 25% of the virus-infected subjects in the NAC group developed symptoms, as contrasted to 79% of those of placebo. (Given the carnage that influenza wreaks among the elderly, it is most regrettable that no effort has been made to replicate this study, conducted over 20 years ago.) The particular utility of NAC in the elderly might reflect the fact that plasma cysteine levels and cellular glutathione levels tend to decline with advancing age.20" [Emphasis added]
Beneficial Effects Of NAC For Other Respiratory Conditions
COPD [Chronic obstructive pulmonary disease] patients treated with NAC had fewer exacerbations:
sciencedirect.com/science/a...
"we noted 497 acute exacerbations in 482 patients in the N-acetylcysteine group who received at least one dose and had at least one assessment visit ...and 641 acute exacerbations in 482 patients in the placebo group (... risk ratio 0·78, ... p=0·0011)."
Meta-analysis of use of NAC in COPD:
sciencedirect.com/topics/me...
" A meta-analysis of randomized controlled trials retrieved from PubMed and Medline databases (12 trials; 2691 patients). High-dose [relative ratio (RR) = 0.90...P = 0.041] and low-dose (RR = 0.83... P = 0.043) NAC reduced COPD exacerbation prevalence. Long-term (≥6 months), but not short-term, NAC reduced exacerbation prevalence (RR = 0.85...P = 0.024)."
NAC has been reported to be useful in studies of cystic fibrosis patients:
cysticfibrosisjournal.com/a...
" Results: Lung function (FEV1and FEF25–75%) remained stable or increased slightly in the NAC group but decreased in the placebo group"
High-dose oral N-acetylcysteine, a glutathione prodrug, modulates inflammation in cystic fibrosis:
pnas.org/content/103/12/462...
" N-acetylcysteine, given orally in high doses (0.6 to 1.0 g three times daily, for 4 weeks). ... Consistently, neutrophil burden in CF airways was decreased upon treatment (P = 0.003), as was the number of airway neutrophils actively releasing elastase-rich granules (P = 0.005)...positive treatment effects ... included decreased sputum IL-8 levels (P = 0.032). "
Please be aware that some animal studies have found potential adverse effects: Here is a study showing NAC caused pulmonary arterial hypertension (PAH) in an animal model:
jci.org/articles/view/29444...
PAH is a serious and relatively unusual condition. When there was a rash of cases of PAH caused by a diet pill combination it was rapidly tracked down to the source. NAC is a common supplement. If it were causing PAH in humans it seems likely it would have been noticed. Poor exercise tolerance is a symptom of PAH. I personally have been taking NAC for years and have excellent exercise tolerance. That said, I am in no position to make any guarantee to others regarding NAC and PAH.
Another study found NAC accelerated development of cancer in an animal model:stm.sciencemag.org/content/...
insight.jci.org/articles/vi...
blogs.sciencemag.org/pipeli...
Apparently this was a result of NAC being an antioxidant, preventing DNA damage, and down regulating the p53 gene as a result. This concern applies to any antioxidant, such as vitamin E which was also found to have the same effect. For what is worth, folate supplementation is even worse - has been demonstrated to increase cancer incidence in humans. I wrote about that here - Folate Supplementation Carcinogenic tinyurl.com/ycdrz5lj
For important additional perspective on this see comment by rescuema here:
healthunlocked.com/parkinso...
Although I do take NAC myself, in view of the foregoing I cannot say whether anyone else should take it or not. Each person must decide for him or herself whether the benefits sufficiently outweigh the risks to make NAC supplementation appropriate.
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Update - Dr. Seheult with additional information: