Glycine is a cheap, sweet-tasting amino acid found in skin, bone and connective tissue, sold as a powder for sleep, antioxidant support and longevity. A few grams before bed shortens the time to fall asleep and lowers next-day tiredness — the most repeatable finding. Paired with a sulfur-containing partner it improved walking speed and grip strength in older adults. Longer life has been shown only in animals. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Fasting plasma glycine | 200–300 µmol/L | Confirms the dose is reaching the bloodstream |
| Whole-blood glutathione | 1.8–2.6 mmol/L red blood cells | The pathway glycine is supplemented to support |
| Homocysteine | 5–8 µmol/L | Glycine has raised it in one study |
| Fasting insulin | 2–5 µIU/mL | Insulin resistance lowers circulating glycine and predicts who responds |
| ALT and AST | ALT 10–20 U/L, AST 10–25 U/L | Liver enzymes fell in the obesity study and mark fatty-liver change |
| eGFR with serum creatinine | Above 90 mL/min/1.73 m² | Defines the dose ceiling and the oxalate handling capacity |
| 24-hour urinary oxalate | Below 30 mg per 24 hours | The specific risk glycine could plausibly raise through glyoxylate |
| Systolic blood pressure | 110–120 mmHg | Glycine lowered it in metabolic syndrome; additive hypotension is the concern |
| High-sensitivity C-reactive protein | Below 1.0 mg/L | Tracks the inflammation that glutathione restoration is meant to reduce |
| Sleep-onset latency | No established target; the change from the individual's own pre-glycine baseline | The endpoint glycine most reliably moves |
Cadence: Tolerance and blood pressure at 2 weeks; homocysteine and liver enzymes at 12 weeks; full panel including kidney function and oxalate at 6 months, then every 6–12 months on continued use.