Glycine for Parasympathetic Activation

Glycine before bed improves sleep quality and lowers core temperature, indirectly supporting overnight parasympathetic recovery.

Overview

Glycine before bed improves sleep quality and lowers core temperature, indirectly supporting overnight parasympathetic recovery.

Verdict

Mixed evidence

How It Works

Glycine acts on NMDA receptors in the suprachiasmatic nucleus, promoting peripheral vasodilation and the core temperature drop that initiates sleep.

Dosing & Protocol

Typical dose

Recommended dose: 3g, 30-60 minutes before bed
Expected timeframe: 1-2 weeks

Protocol

form: Powder in water or capsules
duration: 2-4 weeks
co factor: Take before bed. Evidence is mixed and partly indirect. Glycine is an inhibitory neurotransmitter acting at strychnine-sensitive glycine receptors in the brainstem and spinal cord, and the vasodilation and core temperature drop seen after 3 g before bed are consistent with a shift toward parasympathetic dominance at sleep onset. Some studies report changes in heart rate variability and reduced sympathetic tone with glycine, and animal work supports an effect on autonomic outflow. But human data are limited, heart rate variability outcomes are inconsistently reported and easily confounded by breathing and posture, and no trial has tested glycine as a daytime autonomic intervention. Slow-paced breathing at around six breaths per minute has better evidence for the same goal.
titration: No titration; 3 g is the studied dose
starting dose: 3 g glycine in water 30-60 minutes before bed

Evidence

What the studies say

Small Japanese trials show improved subjective sleep quality and reduced next-day fatigue at 3g before bed, with polysomnography showing faster sleep onset. HRV was not a primary endpoint in these studies.

No studies are yet linked to both Glycine and Parasympathetic Activation.

Safety

Caveats

Effects are on sleep quality rather than HRV directly. Generally well tolerated; mild GI upset at higher doses.

Less likely to help if

People seeking daytime autonomic effects, which have not been tested.

Medical Disclaimer

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Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.