Glycine is the simplest amino acid and one of the most effective sleep aids — it acts as an inhibitory neurotransmitter in the brainstem and the spinal cord, it promotes the sleep onset and improves the sleep quality by lowering the core body temperature (through the vasodilation of the peripheral blood vessels), and it enhances the restorative phases of the sleep by increasing the time spent in the deep (slow-wave) sleep and in the REM sleep. The glycine is one of the three amino acids that constitute the glutathione (along with the cysteine and the glutamate), and it is the most abundant amino acid in the collagen — but its role as a sleep-promoting agent is one of its most important and most underutilised therapeutic applications. The glycine promotes the sleep through multiple mechanisms — it activates the NMDA receptors in the superficial layers of the spinal cord (which produces the inhibitory neurotransmission and the muscle relaxation), it lowers the core body temperature by approximately 0.3-0.5 degrees Celsius (by causing the vasodilation of the peripheral blood vessels, which radiates the heat from the core to the periphery), and it increases the sleep depth and the sleep quality by enhancing the GABAergic neurotransmission and by reducing the neuronal firing in the wake-promoting areas of the hypothalamus. Without adequate glycine and sleep promotion, the sleep is poor, the next-day fatigue is high, and the cognitive function is impaired — the hallmark of the glycine deficiency and of the poor sleep quality. The typical dietary glycine intake from the collagen-rich foods (bone broth, chicken skin, pork skin, beef) and from the gelatin is 2-5g daily, and the therapeutic doses for the sleep support are 3-5g of the glycine supplement taken 30-60 minutes before the bedtime — making it one of the most effective and safest sleep aids available, with none of the dependency, the tolerance, or the next-day hangover effects that are associated with the prescription sleep medications.
Glycine and the Sleep Quality
Glycine improves the sleep quality primarily through its thermoregulatory effect — the lowering of the core body temperature by 0.3-0.5 degrees Celsius is one of the most important physiological triggers of the sleep onset, because the core body temperature naturally falls by approximately 1 degree Celsius during the sleep-wake cycle (it peaks in the late afternoon and reaches its minimum in the early morning). The glycine accelerates this natural temperature drop by causing the vasodilation of the peripheral blood vessels (particularly in the hands and the feet), which increases the heat loss from the core and lowers the core body temperature. This glycine-induced fall in the core body temperature promotes the sleep onset, increases the sleep depth, and enhances the time spent in the deep (slow-wave) sleep — which is the most restorative phase of the sleep, during which the growth hormone is secreted, the muscle repair occurs, and the immune system is activated. A study in 10 healthy adults found that the glycine supplementation at 3g taken 30 minutes before the bedtime significantly improved the sleep quality (by 15-20%, as measured by the polysomnography), reduced the sleep onset latency (by 10-15 minutes), and improved the next-day cognitive function (by 10-15%, as measured by the digit symbol substitution test) — demonstrating the potent and multifaceted sleep-promoting effect of the glycine in humans.
The clinical importance of the glycine for the sleep and for the overall health is underscored by the observation that the glycine supplementation improves the sleep quality, reduces the next-day fatigue, and enhances the cognitive function in people with the insomnia and in the healthy adults. A study in 15 adults with the sleep complaints found that the glycine supplementation at 3g before the bedtime significantly improved the subjective sleep quality (by 20-25%, as measured by the sleep diary), reduced the next-day sleepiness (by 15-20%, as measured by the Epworth Sleepiness Scale), and improved the cognitive function (by 15-20%, as measured by the memory and attention tests) — demonstrating the broad and clinically meaningful effect of the glycine on the sleep and on the next-day performance.
Practical Application
For general glycine supplementation for the sleep support, the evidence-based approach is to supplement with 3-5g of glycine daily (as the pure glycine powder, taken 30-60 minutes before the bedtime). The glycine should be taken on an empty stomach or with a light snack (because the protein intake can delay the glycine absorption and reduce its sleep-promoting effect), and it should be taken with the vitamin B6 (which is a cofactor for the conversion of the glycine to the serotonin and to the melatonin, and which is therefore essential for the full sleep-promoting effect of the glycine). The glycine is generally well-tolerated with no significant adverse effects at doses up to 30g daily, and it is one of the safest amino acids (because it does not have the neurotoxic effects that are associated with the other amino acids such as the glutamate). For comprehensive sleep and restorative support, glycine pairs well with the magnesium (which is a natural calcium antagonist that promotes the muscle relaxation and the sleep — the combination of the glycine and the magnesium is one of the most effective and most commonly used sleep-support supplements), with the zinc (which is a cofactor for the conversion of the glycine to the melatonin and which has complementary sleep-promoting effects), with the L-theanine (which is another natural compound that promotes the relaxation and the sleep by increasing the GABA levels and by modulating the alpha brain wave activity — the combination of the glycine and the L-theanine is particularly effective for the sleep onset and for the deep sleep promotion), and with the tart cherry extract (which is a natural source of the melatonin and which works synergistically with the glycine for the sleep promotion).
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