GlycineNew

Reviewed Sep 19, 2026

Glycine is the rate-limiting amino acid for making glutathione, the body's principal intracellular antioxidant, and most of the recent longevity interest in glycine comes from GlyNAC — a combination of glycine and N-acetylcysteine (a cysteine precursor). In a 16-week randomized, placebo-controlled trial in 24 older adults (GlyNAC vs an isonitrogenous alanine placebo), the GlyNAC group — and not placebo — showed corrected red-cell glutathione deficiency and improvements across several aging-related measures, including roughly 19% faster gait speed (approaching young-adult controls), about an 80% reduction in a marker of oxidative stress (TBARS), large reductions in the inflammatory cytokines IL-6 (~83%) and TNF-α (~58%), and roughly a 68% improvement in insulin resistance (HOMA-IR), alongside gains in muscle strength, exercise capacity, mitochondrial fuel oxidation and body composition (Kumar et al., J Gerontol A Biol Sci Med Sci, 2023; earlier 24-week open-label pilot: Kumar et al., Clinical and Translational Medicine, 2021). These findings are striking but come from small, single-center trials, and the benefits waned after supplementation stopped. Importantly, an independent, larger, industry-run randomized trial of GlyNAC in 114 healthy older adults did not meet its primary endpoint: 2 weeks of supplementation did not raise total glutathione or the glutathione redox ratio overall, with a signal only in a pre-specified subgroup that had high baseline oxidative stress and low glutathione (Lizzo et al., Frontiers in Aging, 2022). Glycine on its own has a separate, modest evidence base for sleep quality at about 3 g before bed. Overall the aging data are early and mixed, and larger, longer, independent trials are needed; GlyNAC-style benefits should not be assumed from glycine alone. Glycine is generally well tolerated. This information is educational and is not medical advice or a claim to diagnose, treat, cure or prevent any disease — discuss supplementation with your physician, particularly if you take other medications.