Glycine and NAC supplement in older adults: pilot trial results
What it found
In a small pilot trial, 24 weeks of a glycine and N-acetylcysteine supplement improved several age-related measures in older adults, but benefits faded after stopping it for 12 weeks.
What they found
Studies in people
Glutathione and oxidative stress
Before supplementation, older adults had 76% lower red-blood-cell reduced glutathione and higher markers of oxidative stress than younger adults. After 24 weeks of the supplement, glutathione rose 200% and oxidative stress markers fell. These benefits declined after stopping the supplement for 12 weeks.
Mitochondrial fuel oxidation
Older adults had 54% lower mitochondrial fatty-acid oxidation and 51% higher mitochondrial glucose oxidation than younger adults. The supplement corrected these defects, but the improvements were lost after stopping it.
Inflammation and endothelial function
Older adults had higher levels of inflammatory markers and signs of endothelial dysfunction than younger adults. After 24 weeks of the supplement, these markers improved, but the benefits reversed after stopping it.
Insulin resistance and blood sugar
Older adults had 571% higher insulin resistance than younger adults. The supplement lowered fasting glucose by 9%, insulin by 55%, and insulin resistance by 59%. These improvements declined after stopping the supplement.
Muscle strength and physical function
Older adults had slower gait speed, lower grip strength, and poorer exercise capacity than younger adults. After 24 weeks of the supplement, gait speed improved to match younger adults, and grip strength and exercise capacity also improved. These benefits declined after stopping the supplement.
Cognition
Older adults had lower cognitive test scores and lower levels of a brain biomarker than younger adults. The supplement improved performance on all cognitive tests, but scores declined after stopping it.
Body composition
Older adults had higher body fat and waist circumference than younger adults. The supplement was linked to a 4% decrease in fat mass and a 4 cm reduction in waist circumference. These benefits began to reverse after stopping it.
Side effects
No side effects were reported during the 36-week study, and blood tests for liver and kidney function stayed normal.
What the authors conclude
“The results of this trial suggest that GlyNAC supplementation in OA is well tolerated and could play a novel role in improving healthy aging in OA by correcting GSH deficiency, OxS, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, body fat, muscle strength, gait speed, and cognitive function.”
Also in their conclusions
- They say GlyNAC supplementation in older adults was well tolerated and could play a novel role in improving healthy aging by correcting glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, body fat, muscle strength, gait speed, and cognitive function.
- They note that GlyNAC supplementation also appears to improve hallmark defects in aging, which could be an exciting discovery and needs to be confirmed in future studies.
- They support the need for future trials to assess the effects of GlyNAC supplementation in a larger population of older adults receiving it for a longer duration.
How it was done
The authors wanted to test whether supplementing glycine and N-acetylcysteine could correct glutathione deficiency and related problems in older adults, since effective interventions for these age-related defects are limited or lacking.
Eight older adults (aged 71 to 80) took a glycine and N-acetylcysteine supplement for 24 weeks, then stopped for 12 weeks. Eight younger adults (aged 21 to 30) were studied once for comparison and did not take the supplement.
What it can’t tell you
- This was a small pilot trial with only eight older adults and no placebo group, so the results may not apply to all older people.
- The study cannot show whether GlyNAC lowers cancer risk or affects long-term health outcomes.
- The findings need to be confirmed in larger, blinded trials.
Who paid
- Conflicts
- None of the authors have any conflicts of interest to disclose.
- Authors work at
- Baylor College of Medicine, USA; USDA/ARS Children's Nutritional Research Center, USA; Institute of Clinical and Translational Research, Texas
The paper
- Title
- Glycine and N-acetylcysteine (GlyNAC) supplementation in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, genotoxicity, muscle strength, and cognition: Results of a pilot clinical trial
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Kumar P, Liu C, Hsu JW, et al (2021). Glycine and N-acetylcysteine (GlyNAC) supplementation in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, genotoxicity, muscle strength, and cognition: Results of a pilot clinical trial. Clinical and translational medicine. doi:10.1002/ctm2.372Free full textPubMed 33783984DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error