GlyNAC: what happens when glycine and NAC are taken together?

This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.

Summary

GlyNAC is the combination of glycine and N-acetylcysteine, taken together as precursors of glutathione, the main antioxidant inside cells. A 16 week randomised placebo controlled trial in 24 older adults, published in 2023 by a Baylor research group in Houston, reported improvements in glutathione levels, markers of oxidative stress, and physical function compared with placebo. A larger dose ranging trial in 114 healthy older adults found no overall increase in blood glutathione over two weeks, with an effect confined to a subgroup with low baseline glutathione and high oxidative stress. The evidence base is small and early rather than established. Both components are available as single supplements in the UK.

How it works

Glutathione is a small molecule built inside cells from three amino acids, which are glutamate, cysteine and glycine. The Baylor research group reported that older adults in their studies showed lower availability of cysteine and glycine, and proposed that this limits how much glutathione cells can make. N-acetylcysteine, usually shortened to NAC, supplies cysteine in a stable form. Taking glycine alongside NAC supplies both of the two amino acids the group identified as limiting, which is the rationale for the combination.

Effective dose

The 2023 randomised trial dosed both components by participant body weight in a one to one ratio. The dose ranging trial in 114 healthy older adults tested combined daily amounts of 2.4, 4.8 and 7.2 grams, split across two doses per day, also in a one to one ratio. No standard dose exists, and no UK guideline addresses one. For the single products sold in the UK, the label dose on each product is the reference point.

Forms compared

GlyNAC is not a single compound. It is two supplements taken together, and the trials used plain glycine powder or capsules alongside standard NAC. Some manufacturers sell pre-mixed capsules under the GlyNAC name. The trial evidence applies to the combination of the two components in a one to one ratio rather than to any particular branded product.

Timing

The dose ranging trial split the daily amount across two doses. No evidence reviewed here supports a particular time of day. Taking NAC with food is a common approach for tolerability.

Safety profile

Both randomised trials reported the combination as safe and well tolerated at the doses tested over their durations, which were 16 weeks in the smaller trial and two weeks in the larger one. Longer term safety data for the combination does not yet exist. NAC has a long history of clinical use, and glycine is an amino acid present in everyday protein foods, but the safety statements above apply to the doses and durations the trials actually tested.

Special populations

The trial evidence is in adults aged roughly 60 and older, plus small young adult comparison groups. No trials of the combination in pregnancy were found, so no statement can be made for that group beyond the general advice to discuss supplements with a midwife or GP. Findings in older adults should not be assumed to transfer to younger people, and the dose ranging trial reported its clearest effect in people who started with low glutathione and high oxidative stress rather than in healthy participants generally.

Interactions

Interaction questions for the combination follow its components, and NAC carries the greater share of documented considerations in the wider literature. Glycine at supplemental doses has few documented interactions in the sources reviewed. Anyone taking either component alongside prescriptions should raise it with a GP or pharmacist, and Nutri365 checks for interactions and contraindications when reading a plan.

Guideline positions

No NHS or NICE guidance addresses GlyNAC. The NIH Office of Dietary Supplements has no fact sheet for the combination. The evidence base consists of individual registered trials, of which the two randomised trials summarised here are the principal ones. That is an honest description of where the evidence currently stops.

Practical framework

Reproducing the trial approach means taking glycine and NAC in a one to one ratio, split across the day, at amounts within the labels of the products used. Both components are stocked as single products, and N-acetyl cysteine capsules are available at nutritailor.co.uk/products/n-acetyl-cysteine with glycine sold separately. The trial populations were older adults, and the larger trial reported its effect only in the subgroup with low baseline glutathione, which is worth weighing before adding the combination. Nutri365 reads your results and history over time, checks for interactions and contraindications, and refers questions outside scope to a GP or a BANT registered nutritional therapist.

Common misconceptions

GlyNAC is sometimes described as a single novel compound, but it is two established supplements taken together. It is also sometimes equated with taking glutathione itself, yet the combination supplies precursors and the trials measured whether cells then made more glutathione. Media coverage has described the Baylor findings as an ageing intervention, and the trial authors themselves describe the evidence as early, with the larger dose ranging trial finding no overall glutathione increase in healthy older adults.

Sources

Kumar P, Liu C, Suliburk J, Hsu JW, Muthupillai R, Jahoor F, Minard CG, Taffet GE, Sekhar RV 2023. Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial. Journals of Gerontology Series A 78(1):75-89, DOI 10.1093/gerona/glac135.
Kumar P, Liu C, Hsu JW, Chacko S, Minard C, Jahoor F, Sekhar RV 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 11(3):e372, DOI 10.1002/ctm2.372.
Lizzo G et al. (NCT05041179) 2022. A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage. Frontiers in Aging (PMC).

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