Primary Research · 2012
New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep
Bannai and Kawai · Journal of Pharmacological Sciences, 2012
Key finding
3g glycine before bed improved subjective sleep quality and next-day fatigue scores.
Abstract
PubMed · PMID 22293292 →Glycine is a non-essential amino acid that has indispensable roles in both excitatory and inhibitory neurotransmission via N-methyl-D-aspartate type glutamate receptors and glycine receptors, respectively. We recently reported that glycine ingestion before bedtime significantly ameliorated subjective sleep quality in individuals with insomniac tendencies. Oral administration of glycine to rats was found to induce a significant increase in the plasma and cerebrospinal fluid glycine concentrations and a significant decrease in the core body temperature associated with an increase in cutaneous blood flow. The decline in the core body temperature might be a mechanism underlying glycine's effect on sleep, as the onset of sleep is known to involve a decrease in the core body temperature. Moreover, a low core body temperature is maintained during sleep in humans. Pharmacological studies investigating the mechanisms of glycine on sleep were also performed. In this review, we will describe both our recent findings regarding how and where orally administered glycine acts and findings from our rat study and human trials.
Abstract sourced from PubMed, a database of the U.S. National Library of Medicine. Displayed in the authors’ own words for context; our critique is in the sections below.
Read the full paper
Cited in 3 guides
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How to read a study like this
The same questions worth asking about any research paper, not just this one. Worth a minute even if you trust the grade.
Who was studied, and do you resemble them?
Supplement effects often depend on baseline status. Vitamin D helps people who are deficient; iron helps people who are anemic. A result in people unlike you may not apply to you.
What was measured, and does it matter in daily life?
A study that shows a blood marker moved isn't the same as a study that shows people felt or functioned better. Ask what the outcome means in practice.
How large was the effect — not just whether it was significant.
'Statistically significant' only means the effect is unlikely to be zero. It doesn't tell you the effect is large enough to notice. Look for effect sizes, not just p-values.
Who paid for the trial, and what did they stand to gain?
Industry-funded trials are several times more likely to report positive results than independent ones. It's not usually fraud — it's subtle design and reporting choices. Weight accordingly.
Has anyone else replicated this?
Single positive trials are hypotheses. Replication by independent groups is what turns a hypothesis into reliable evidence. If the only positive trial is the one you're reading, wait.
Does the dose in the trial match what's being sold?
Supplement marketing routinely cites trials that used 5–10× the dose in the product. If the effective dose was 2 g/day and the capsule has 200 mg, expect roughly no effect.
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