Glycine — The Collagen Amino Acid
Glycine is the simplest amino acid and the most abundant in collagen. It is conditionally essential in aging, as endogenous synthesis declines. Glycine supplementation extended lifespan in male and female mice in the NIA Interventions Testing Program, and supports methylation, sleep quality, and joint health.
Mechanism of Action
Glycine is a precursor to glutathione (the master antioxidant), collagen (structural protein), creatine, and porphyrins (heme). It acts as an inhibitory neurotransmitter in the spinal cord (improving sleep quality) and activates NMDA receptors in the brain. Glycine + NAC (GlyNAC) supplementation restores glutathione levels that decline with age.
Human Trial Evidence
A 2021 Clinical and Translational Medicine RCT (Kumar et al.) showed GlyNAC (glycine + N-acetylcysteine) supplementation for 24 weeks in older adults corrected glutathione deficiency, reduced oxidative stress, improved mitochondrial function, and improved physical strength. A 2017 Sleep RCT showed 3 g glycine before bed improved sleep quality and reduced daytime sleepiness.
Dosing Protocol
3–10 g/day. Sleep: 3 g 30 minutes before bed. GlyNAC protocol: 1.33 mg/kg glycine + 0.81 mg/kg NAC twice daily. Collagen support: 10–15 g/day (often from collagen peptides). Glycine is inexpensive and has a mildly sweet taste.
Safety & Contraindications
Excellent safety profile. No adverse events in trials up to 60 g/day. Glycine is an endogenous amino acid found in all protein-containing foods. No known drug interactions at supplemental doses.