Evidence Trace, complete trial record
In plain terms
In plain terms: GlyNAC (Glycine + N-Acetylcysteine) shows early signals in human research but the evidence is limited -- small trials, surrogate endpoints, or not yet independently replicated. It is an emerging area, not yet a proven one.
GlyNAC (Glycine + N-Acetylcysteine)
C
Limited: small, mixed or unreplicated trials
The endpoint this grade is based on: Surrogate biomarker endpoint, Use-specific. In healthy older adults the primary endpoint was null in the one trial not run by the originating group, a 2-week trial sponsored by a company that holds patents on and markets glycine plus NAC products. In older adults randomized by the originating group for 16 weeks at a far higher dose, glutathione and downstream markers improved; that population was not selected for high oxidative stress, and the 'elevated demand' subgroup comes from the sponsor trial's post hoc analysis.
The evidence as the record states it
Kumar, Sekhar et al. (J Gerontol A Biol Sci Med Sci, 2023; PMID 35975308): 24 older adults randomized to GlyNAC or isonitrogenous alanine placebo for 16 weeks, NIH-funded; GlyNAC and not placebo corrected glutathione deficiency in red blood cells, lowered oxidative stress, improved mitochondrial fuel oxidation, lowered insulin resistance and inflammation, improved endothelial markers and systolic blood pressure, and increased gait speed and grip strength. The abstract does not state a BMI entry criterion. The Grade C rests on this trial. Kumar et al. (Clin Transl Med, 2021; PMID 33783984) is a 24-week open-label pilot in 8 older adults with no placebo group; supporting context that does not carry the grade. Lizzo et al. (Front Aging, 2022; PMID 35821844): randomized controlled trial, 114 healthy older adults, 2.4, 4.8 or 7.2 g/day total for 2 weeks; no change in the reduced-to-oxidized glutathione ratio or total glutathione, the primary endpoint; run and sponsored by a company that holds and licenses patents on glycine plus N-acetylcysteine and markets the products, so the null result came from the product's commercial owner. Its dose (2.4 to 7.2 g/day) and duration (2 weeks) are far below the originating group's protocol of about 100 mg/kg/day of each amino acid, roughly 14 g/day total, for 16 weeks.
PMID 35975308 PMID 33783984 PMID 35821844
Evidence by specific use
Glutathione redox status in healthy older adults
Grade D
This is the only trial of GlyNAC not run by the originating group and it missed its primary endpoint in healthy older adults; it was sponsored by the product's commercial owner and used a lower dose for a shorter time.
PMID 35821844
Glutathione, oxidative stress and aging markers in older adults (originating group's trial)
Grade C
Kumar and Sekhar's one randomized placebo-controlled trial, in 24 older adults for 16 weeks (PMID 35975308), reports benefit on glutathione and downstream aging markers; the 2021 older-adult study (PMID 33783984) and the group's HIV and type 2 diabetes studies are open-label pilots. The trial randomized older adults, not people selected for high oxidative stress or low glutathione; the 'elevated demand' subgroup comes from the sponsor trial's post hoc analysis, not from how anyone was enrolled. The entire positive evidence base originates from a single investigator group at Baylor. The one trial by another group, in HEALTHY older adults at a lower dose for 2 weeks, was null on its primary endpoint but found a signal post hoc in the subset with high oxidative stress and low baseline glutathione. The two results are compatible. That is why this use holds at C rather than dropping to D: the other trial did not contradict the effect at the originating group's dose and duration, which it did not test.
PMID 35975308 PMID 33783984
Why Grade C and not Grade B
Grade C reflects early or limited human evidence -- small trials, surrogate endpoints, or preliminary findings not yet independently replicated. The evidence points in a promising direction but does not yet meet the standard for Grade B. A single well-powered, independently replicated trial with a meaningful endpoint would move this to Grade B or higher.
What would move this grade
A well-powered randomized trial with an objective, clinically meaningful primary endpoint and at least one independent replication would support Grade B or higher.
How to track whether this is working
The trials measured clinical outcomes relevant to the indication, including grip strength, walking performance and glycemic measures.