Glycine

What is glycine?

Glycine is the smallest and simplest amino acid, with just a single hydrogen atom as its side chain. Despite that simplicity, it's one of the most metabolically active molecules in the body. Glycine makes up roughly a third of all collagen, serves as a building block for glutathione (the body's main intracellular antioxidant), acts as a precursor to creatine, and functions as an inhibitory neurotransmitter in the brain and spinal cord ^[1]. The body synthesizes about 3 g of glycine per day on its own, but researchers estimate that humans actually need around 10 g daily to meet all biosynthetic demands — creating a consistent shortfall that grows worse with age ^[2].

Glycine and aging

The longevity case for glycine got serious when the NIA Interventions Testing Program found that an 8% glycine diet extended lifespan in genetically diverse mice by 4–6% at all three independent test sites ^[3]. That may sound modest, but few compounds clear the bar of this rigorous multi-site program. One proposed mechanism: glycine mimics methionine restriction. The enzyme GNMT uses glycine to clear excess methionine by converting it to sarcosine, effectively lowering the methionine load without actually eating less of it ^[1].

Glycine also drew attention through GlyNAC — a combination of glycine and N-acetylcysteine developed by Dr. Rajagopal Sekhar's lab at Baylor College of Medicine. In a randomized controlled trial, older adults who took GlyNAC for 16 weeks showed improvements in glutathione levels, oxidative stress, mitochondrial function, inflammation, insulin resistance, gait speed, and muscle strength. The supplement also improved or corrected 7 hallmarks of aging, including cellular senescence and genomic damage ^[4]. In mice, GlyNAC supplementation increased lifespan by 24% ^[5].

Sleep quality

Taking 3 g of glycine before bed has been shown to improve subjective sleep quality, shorten the time to fall asleep, and reduce next-day fatigue in people with poor sleep. In one study, glycine shortened both sleep onset latency and latency to slow-wave sleep without changing overall sleep architecture ^[6]. The mechanism appears to involve NMDA receptors in the suprachiasmatic nucleus: glycine triggers peripheral vasodilation, which drops core body temperature — the same signal the body uses naturally to initiate sleep ^[7]. It's a simple, well-tolerated intervention that doesn't carry the grogginess of pharmaceutical sleep aids.

Neuroprotection and brain health

Glycine crosses the blood-brain barrier and acts on NMDA receptors involved in learning and memory. In mouse models of accelerated aging, glycine administration reversed oxidative stress, neuroinflammation, and memory impairment through JNK pathway deactivation ^[8]. The GlyNAC combination showed similar promise for the brain specifically: supplementation in old mice corrected brain glutathione deficiency, restored glucose transporter expression, improved mitochondrial function, and reversed age-associated cognitive decline ^[9].

Dosage and supplementation

Most clinical studies on sleep use 3 g before bedtime. For broader metabolic and anti-aging benefits, the GlyNAC protocol used glycine at 100 mg/kg/day (roughly 7–8 g for a 75 kg person) alongside N-acetylcysteine at the same dose ^[4]. A 2024 systematic review noted that glycine is generally well-tolerated across a wide dosing range, with the nervous system showing the most consistently positive effects. Side effects are rare at typical supplement doses (3–10 g/day) ^[10]. Glycine powder dissolves easily in water and has a slightly sweet taste, making it one of the more pleasant amino acid supplements to take.

Food sources

Collagen-rich animal foods are the best dietary sources: bone broth, skin-on poultry (about 3.3 g per 100 g of chicken skin), pork rinds, and gelatin. Red meat and fish provide roughly 1.5–2 g per 100 g serving. Plant sources include soybeans, lentils, peanuts, and spinach, though in much lower concentrations. Since the average Western diet provides only about 2–3 g of glycine daily and the body's own synthesis adds another 3 g, supplementation is the most practical way to close the estimated 4–5 g daily gap.