I wonder if the glycine might somehow prevent cancers.
I did post a NAC use study for use with COVID some months back, but that described it helping reduce lung issues while having COVID, but had also mentioned that a 600 mg dose of just NAC could be used as a preventative dose for likely exposure occasions, while up to 2,400 mg could be used from supplements for more serious lung issues, if progressing into pneumonia or ARDS. However, this was for short-term use occasions.
Nestle is selling the combination of both NAC and glycine, as 600 mg each, as a daily amount. However, they also have two other supplements, to be bought separately, that complement the GlyNAC, one of which appears to greatly increase apoptosis of defective mitochondria. That particular supplement has Urolithin A in it (500 mg/day), which is a dose that was used in another study, showing its benefits.
Your posted study appears to mention that it NAC is helping defective cells survive - cells that are capable of devolving into cancer - that have otherwise been sidelined, but not cleared out by normal processes, in part, due to those processes having broken down, too. I can see how a substance could bring back to life both good and bad cells, largely due to revitalizing their mitochondria. However, the processes we have to eliminate problem mitochondria and cells should also be revitalized, and appear to be, from the nature of the GlyNAC study's tests showing glutathione being generated everywhere they tested.
Is it made less concerning by adding the glycine? The glycine is supposed to help convert the NAC, and this combination also made mice live 24% longer lives in a separate study. According to your posted study, 10% of normal aged mice used in the 24% longer life study should have had lung cancer, if GlyNAC, as opposed to just NAC-only (again, your study), caused problems with lung cancer. I will say that in the 24% longer life study, the mice got GlyNAC only when they entered old age, as opposed to being given it from conception (fed to mother at 40 mM concentration in all liquids) through to old age (40 mM concentration in all liquids), for just the NAC, in your study.
The GlyNAC longer life study:
“GlyNAC supplementation extends life span in mice (Equal parts glycine and NAC)”
https://freerepublic.com/focus/f-chat/4044707/posts
From the study this thread initially referenced (“GlyNAC improves multiple defects in aging to boost strength and cognition in older humans”):
“This study also answers the question of why GlyNAC is an improvement over supplementation with NAC alone. GSH synthesis requires two biochemical steps – in the first step cysteine is added to glutamic acid to form the intermediate glutamylcysteine, and in the second step glycine is added to glutamylcysteine to form GSH. Via translational studies in aged mice, we discovered and reported that GSH adequacy is critically important for optimal and efficient mitochondrial fatty-acid oxidation (MFO) in rodents and OA. Because the impact of longer duration of supplementing GlyNAC in OA was unknown, we conducted a 36-week open-label trial to test whether supplementing GlyNAC for 24-weeks in OA could improve or correct age-associated GSH deficiency, OxS, impaired MFO, inflammation, endothelial dysfunction, insulin resistance, muscle protein loss, and body composition, and whether this could impact cognitive function, gait speed, muscle strength, and exercise capacity. The trial also assessed whether any accrued benefits would decline after stopping GlyNAC for 12 weeks.”
As stated immediately above, cysteine is added to one step, with glutamic acid, then the glycine is added to a second needed step, with glutamylcysteine, which is what creates the final end product needed in all cells to keep their glutathione levels good. Young people can generate the needed glycine and cysteine an normal amounts so adding more cysteine may not be helpful, but in your study, young mice fed NAC-only from conception to young adulthood did already have more problems than the control mice never fed NAC, so I'd say adding cysteine alone to young people should be limited to “as needed” does, such as when NAC is administered for breaking up phlegm in cold remedies, to be safe.
In light of your study, would I chronically take NAC by itself, without glycine? No, again, to be safe. No study speaks to what NAC, not used for a glutathione reaction, does in the body. Does it build up? Does it get used in a process that is going bad? It would preliminarily seem that, at least by itself, it stops a normal process that gets rid of cells or their mitochondria that are beginning to go bad, but there were big differences between the studies and what was given and for how long. In that light, I still feel comfortable with the GlyNAC for myself and my wife and others, in the generally low dose of 600 mg glycine and 600 mg NAC, administered at the same time.