Glycine

Glycine is the simplest amino acid: a single hydrogen atom for a side chain. The body uses it to build collagen, to make glutathione, and as an inhibitory neurotransmitter in the spinal cord. It is not exotic. It is also cheap, roughly a dollar per month at standard doses.

The cleanest evidence for glycine on its own concerns sleep. Three small trials from a Japanese research group at the Osaka Bioscience Institute, run between 2006 and 2012, tested 3 g of glycine before bedtime. The 2012 paper in the Journal of Pharmacological Sciences reported that glycine ingestion before bed improved subjective sleep quality in people with mild insomnia symptoms, correlating with polysomnographic shifts toward faster onset of slow-wave sleep [1]. All three studies used small samples, ran three to four nights, and were conducted by researchers with financial ties to Ajinomoto, a major glycine manufacturer. That does not make the finding false, but it narrows how much weight it can bear.

The bigger longevity claim for glycine comes packaged with N-acetylcysteine, not from glycine alone. A pilot clinical trial from Baylor College of Medicine gave older adults combined glycine and NAC, branded GlyNAC, for 24 weeks and reported correction of glutathione deficiency, reduced oxidative stress, and improvements across inflammation, insulin resistance, muscle strength, gait speed, and cognitive testing compared to baseline and to young-adult controls [2]. This is a real, published, peer-reviewed dataset. It is also a small, single-center, unblinded pilot without a placebo arm in some outcome measures, studying a two-ingredient combination, which means none of it isolates what glycine itself contributes versus what NAC contributes.

What the evidence does not show: nobody has run a large, multi-site, placebo-controlled trial of glycine alone for healthy human lifespan or healthspan extension. The GlyNAC pilot's most informative result may be its withdrawal arm: after the 24-week supplementation period, researchers stopped GlyNAC for 12 weeks and found the glutathione, oxidative stress, and inflammation benefits substantially reversed, with red blood cell glutathione dropping back and oxidative stress markers rising [3]. That is direct evidence against the idea of a lasting biological reset from a temporary course. Whatever GlyNAC does, it appears to require continuous use to sustain, an important caveat that marketing materials built around this trial routinely omit.

Bryan Johnson's Blueprint protocol includes glycine at 1200 mg as part of the official Longevity Mix formula, taken in the morning rather than at bedtime, a scheduling choice that diverges from the sleep-focused literature and reflects a stack-optimization decision rather than a finding from any published sleep trial. This is an n=1 self-report of dosing choice, not evidence about timing efficacy.

Critics of the GlyNAC research point out that the trial design cannot separate glycine's contribution from NAC's, and that a compound outcome improving on a dozen different biomarkers in a small unblinded pilot is exactly the kind of result that looks impressive in a press release and thins out under replication. No independent lab outside the original Baylor group has yet published a replication of the full GlyNAC panel of outcomes.

The honest takeaway: glycine has modest, dated evidence for improving sleep quality at 3 g nightly, and a more ambitious longevity story that currently rests on one small pilot trial of glycine combined with NAC, not glycine by itself.

2026: GlyNAC Reversed 9 Hallmarks of Aging in Humans

A Baylor University trial found that GlyNAC supplementation (glycine + N-acetylcysteine) reversed 9 of 12 classical hallmarks of aging in older adults [1]. The mechanism involves glutathione replenishment: N-acetylcysteine is a precursor to glutathione, the body's primary endogenous antioxidant. GlyNAC is a simple, inexpensive combination of two amino acids, not a proprietary compound. This is one of the few human trials to directly measure aging hallmarks as endpoints rather than clinical outcomes.

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