Benefits
Gait speed and grip strength in older adults
In a 16-week randomized trial, 12 older adults (mean age 71) taking GlyNAC raised gait speed by about 19% (1.13 to 1.34 m/s) and grip strength by about 14%, while the 12 on an alanine placebo did not improve. The paper reports within-group changes rather than direct GlyNAC versus placebo tests, and it is a single small trial.
Glutathione levels in red cells and muscle
In the same trial, red blood cell glutathione rose about 225% and muscle glutathione about 164% in the GlyNAC group, reaching levels seen in young adults. A larger 2-week trial in 114 healthy older adults, run by a company that sells glycine and NAC, found no overall rise in glutathione.
Oxidative stress markers (TBARS, F2-isoprostanes)
Over 16 weeks, the lipid oxidation markers TBARS and F2-isoprostanes each fell about 72% in older adults taking GlyNAC, with no change on placebo. These results come from one small trial; the larger 2-week trial, run by Nestle scientists, did not raise glutathione overall.
Insulin resistance and glucose metabolism
In the 16-week trial, the insulin resistance index HOMA-IR fell about 64% and fasting insulin about 65% in the GlyNAC group, with no change on placebo. This large change comes from 12 people in one small trial and has not been independently confirmed.
Inflammatory markers (IL-6, TNF-alpha, CRP)
After 16 weeks on GlyNAC, IL-6 fell about 78%, TNF-alpha about 54% and hsCRP about 41% in older adults, with no change on placebo. These results come from one small single-team trial and need independent repeating.
Aging hallmark biomarkers
The main trial also measured lab markers linked to aging, such as mitochondrial fuel use, mitophagy, DNA damage and insulin resistance, and reported improvement in many of them after 16 weeks of GlyNAC. These are biomarker changes in 12 people in a single small trial, not proof of slower aging or longer life.
Mechanism of action
Glutathione building blocks
Glutathione is made from glutamate, cysteine and glycine. The Sekhar group proposes that older adults run short of cysteine and glycine, and that supplying them (cysteine as NAC) restores glutathione production.
Mitochondrial function
Glutathione helps protect mitochondria from oxidative damage. In the main trial, GlyNAC improved mitochondrial fatty acid oxidation in older adults, which the authors link to the strength and gait results.
Less oxidative damage
Glutathione neutralizes reactive oxygen species and supports glutathione peroxidase, limiting damage to fats, proteins and DNA. Lipid oxidation markers fell in the main trial.
Inflammatory signaling
Oxidative stress can activate NF-kB and raise inflammatory cytokines such as IL-6 and TNF-alpha. Restoring redox balance is the proposed reason these markers fell in the main trial.
Effects of glycine itself
Glycine also acts in the nervous system and is a building block of collagen and creatine, so some effects of GlyNAC may come from glycine rather than glutathione.
Clinical trials
Randomized, placebo-controlled trial of GlyNAC (100 mg/kg/day each of glycine and NAC) vs isonitrogenous alanine placebo for 16 weeks; 12 young adults took GlyNAC for 2 weeks as a reference group (Kumar et al. 2023, J Gerontol A Biol Sci Med Sci).
24 older adults (12 GlyNAC, 12 placebo) and 12 young adults.
In the GlyNAC group, red cell glutathione rose about 225% and muscle glutathione about 164%; TBARS and F2-isoprostanes fell about 72%; IL-6 fell 78%, TNF-alpha 54% and HOMA-IR 64%; gait speed rose from 1.13 to 1.34 m/s and grip strength about 14%. The placebo group did not improve. Results are reported as within-group changes. No supplement-related adverse events. NIH-funded; no conflicts declared.
Open-label pilot trial: GlyNAC for 24 weeks followed by 12 weeks off, with no placebo group (Kumar et al. 2021, Clin Transl Med).
8 older adults and 8 young adults (young adults studied at baseline only).
After 24 weeks, older adults had higher red cell glutathione and improvements in oxidative stress, mitochondrial function, inflammation, insulin resistance, strength, gait speed, cognition and waist size. Benefits declined after 12 weeks off GlyNAC. Very small and uncontrolled.
Randomized, controlled trial of GlyNAC at 2.4, 4.8 or 7.2 g/day (1:1) vs placebo for 2 weeks (Lizzo et al. 2022, Front Aging).
114 healthy older volunteers (mean age 65), plus 20 young adults for reference.
GlyNAC was safe and well tolerated but did not raise the glutathione redox ratio or total glutathione, the primary outcome (7.2 g vs placebo P=0.739 and P=0.278). A post hoc subgroup with high oxidative stress and low glutathione showed a rise on 4.8 to 7.2 g/day. Authors were employed by Nestle Health Science, which markets glycine and NAC products.