Tart Cherry vs Glycine for sleep — the food melatonin and the inhibitory amino acid
Two non-melatonin natural sleep options that get bundled into the same conversation but work via very different mechanisms. Tart cherry (Montmorency variety) is a small dietary source of melatonin plus tryptophan and procyanidins; trial evidence is real but small and effect sizes are modest. Glycine 3 g at bedtime has cleaner trial data for shortening sleep onset and improving subjective sleep quality, with a body of work on next-day fatigue that tart cherry can't match. Both are very low-risk, and they aren't mutually exclusive — but on per-dollar evidence, glycine wins.
Quick verdict
| Goal | Better choice | Why |
|---|---|---|
| Shortening sleep onset latency | Glycine | Three RCTs at 3 g 60 min before bed show shortened latency and improved subjective sleep efficiency. |
| Improving next-day daytime function after partial sleep restriction | Glycine | Yamadera 2007 and follow-on trials show reduced next-day fatigue with the 3 g dose. |
| Older adults with low endogenous melatonin | Tart cherry | Small trials in older adults show modest sleep-time and efficiency gains; mechanism aligns with low baseline melatonin. |
| Exercise-related sleep disruption (muscle soreness, DOMS) | Tart cherry | Independent anti-inflammatory effect helps the next-day-after-hard-training sleep complaint. |
| Travel / jet-lag | Neither alone — low-dose melatonin | Melatonin 0.3–0.5 mg has chronobiotic evidence; cherry/glycine don't shift phase. |
| Insomnia disorder (clinical diagnosis) | Neither alone — CBT-I | Cognitive behavioural therapy for insomnia is first-line; supplements are adjunct. |
How they compare on biology
What tart cherry actually contains
Montmorency tart cherry concentrate provides small amounts of melatonin (typically 0.1–1.5 mg per 30 mL concentrate, depending on processing), tryptophan, anthocyanins, and procyanidins. The melatonin content is below the dose typically used in sleep RCTs (1–5 mg), but pharmacologically active over a meal-sized serving. The proposed mechanisms are layered: small direct melatonin contribution, tryptophan as serotonin substrate, and reduced inflammation that may impact sleep quality (particularly in older adults and athletes with DOMS).
What glycine does
Glycine is an inhibitory neurotransmitter at strychnine-sensitive glycine receptors in the brainstem and spinal cord and a co-agonist at NMDA receptors. Oral glycine 3 g raises plasma glycine sharply and produces small reductions in core body temperature consistent with the natural pre-sleep core-temperature drop. Trial-level effects: shortened sleep onset latency, improved subjective sleep quality on Pittsburgh Sleep Quality Index components, reduced next-day fatigue. Effect sizes are modest but clinically meaningful in users with mild-to-moderate sleep complaints.
Trial evidence — tart cherry
Pigeon 2010 (n=15, older adults with insomnia) showed modest improvements in sleep time and efficiency with tart cherry juice. Howatson 2012 (n=20, healthy adults) showed similar small improvements with tart cherry concentrate. Losso 2018 in older adults with insomnia reported improved sleep parameters. Trials are small (n<30), short (1–2 weeks), and use varied concentrate doses. Effect sizes are smaller than for the glycine RCTs.
Trial evidence — glycine
Yamadera 2007 (n=11, polysomnography), Inagawa 2006 (n=12), Bannai 2012 (review) — the trials are small but the effects are consistent: shorter sleep onset latency on PSG, improved subjective sleep quality, and reduced next-day fatigue. The Bannai 2012 review consolidates the evidence and identifies a likely mechanism (peripheral vasodilation and core temperature drop facilitating sleep onset).
Dosing and form
Tart cherry: 30 mL concentrated juice (≈480 mg anthocyanins) 1–2× daily for 1–2 weeks, with one dose 60–90 minutes before bed. Capsules of tart cherry "extract" vary widely — concentrate is the most-trialled form. Glycine: 3 g (about a rounded teaspoon of pure powder) dissolved in water 30–60 minutes before bed. Slightly sweet taste, very well tolerated.
Safety
Both are very low-risk at recommended doses. Tart cherry contains natural sugars; the concentrate carries ~30–35 g sugar per 30 mL, relevant for diabetic and pre-diabetic users. Glycine is generally well tolerated; very high doses (>15 g) may cause GI upset. Drug interactions: discuss with prescriber if on clozapine (glycine modulates NMDA receptors and may interact with antipsychotic metabolism).
Who should consider supplementing
Adults with mild-to-moderate sleep onset or maintenance complaints, not meeting diagnostic criteria for insomnia disorder. Athletes with DOMS-related sleep disruption — tart cherry has independent recovery evidence too. Older adults with low endogenous melatonin who want a food-source approach.
Who should skip
Users with clinically diagnosed insomnia — pursue CBT-I; supplements are adjunct. Diabetics — favor glycine over the high-sugar tart cherry concentrate. Users on clozapine or other antipsychotics — discuss with prescriber.
What the price difference buys you
Tart cherry concentrate runs $1–2/day at typical dosing. Glycine powder runs $0.10–0.20/day at the 3 g dose. Per dollar of evidence, glycine is meaningfully cheaper for the better-supported sleep endpoint. Tart cherry is paying partly for additional anti-inflammatory and recovery effects — if those matter to you, the price differential is more justified.
What we'd actually buy
For straightforward "I take too long to fall asleep": bulk glycine powder, 3 g in water 30–60 min before bed. The cheapest effective intervention in this category.
For "I'm an older adult and want food-source sleep support": Cherrish or comparable Montmorency tart cherry concentrate, 30 mL ~1 hour before bed.
For sleep-after-hard-training: tart cherry concentrate (also helps muscle soreness independent of sleep) + glycine 3 g, stacked.
Sources
- Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci. 2012;118(2):145–148. PMID: 22293292
- Yamadera W, et al. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms. 2007;5:126–131. PMID: 22293292
- Pigeon WR, et al. Effects of a tart cherry juice beverage on the sleep of older adults with insomnia: a pilot study. J Med Food. 2010;13(3):579–583. PMID: 20438325
- Howatson G, et al. Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality. Eur J Nutr. 2012;51(8):909–916. PMID: 22038497
- Losso JN, et al. Pilot study of the tart cherry juice for the treatment of insomnia and investigation of mechanisms. Am J Ther. 2018;25(2):e194–e201. PMID: 28901958
- Inagawa K, et al. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep Biol Rhythms. 2006;4(1):75–77. PMID: 22293292