We have previously reported three human volunteer
studies to subjectively assess the effect of glycine on
sleep.
Individuals with continuous complaints about the
quality of their sleep were recruited and given either 3 g
of glycine or a placebo before bedtime. In the first study
(4), a randomized double-blinded crossover trial, 19 female
volunteers (24 – 53 years of age; average, 31.1
years) participated. All of the subjects had complained
about their sleep quality. Their Pittsburgh Sleep Quality
Index (PSQI) scores were 6 or greater, indicating that the
subjects had continuously experienced unsatisfactory
sleep. The subjective quality of sleep was evaluated using
the St. Mary’s Hospital (SMH) Sleep Questionnaire
(24) and the Space-Aeromedicine (SAM) Fatigue Checklist
(25). Glycine significantly improved the feeling of
fatigue the next morning, indicating that glycine helps
improve sleep quality.
The second study (5), a randomized single-blinded
crossover trial, included 11 volunteers (8 females and 3
males; 30 – 57 years of age; average, 40.5 years), whose
mean PSQI score was 8.07, indicating repeated unsatisfactory
sleep. Polysomnographic (PSG) examinations
were performed throughout the night, and the subjective
quality of sleep was evaluated using the SMH Sleep
Questionnaire. Furthermore, daytime sleepiness was assessed
at 08:00, 10:00, 12:00, 21:00, and 23:00 on the
day following the examination. The PSG examinations
revealed a stabilized sleep state and a shortened latency
to both the sleep onset and slow-wave sleep, with no alterations
in the sleep architecture. Glycine also subjectively
improved the volunteers’ satisfaction with their
sleep, the difficulty of sleep onset, and sleep efficiency.
Furthermore, daytime sleepiness was significantly improved
in the morning, as measured by the Visual
Analogue Scale (26). Taken together, these findings indicate
that glycine improves sleep quality both subjectively
and objectively.
No serious side effects have been observed with the
administration of 31 g/day of glycine (27). The third trial
investigated any acute adverse events and daytime
sleepiness after the administration of 9 g of glycine. This
study was an open trial because any safety problems
needed to be addressed quickly if they occurred. A total
of 12 volunteers (6 females and 6 males; 25 – 39 years of
age; average, 34.0 years) participated in the study. Their
mean PSQI score was 4.41, indicating no particular
problems regarding sleep. Glycine (9 g) administered
during the day did not induce sleepiness and had no adverse
effects. Together, the results of these three aforementioned
human trials indicate that glycine improves
sleep quality in a subjective and objective manner and
has no serious adverse effects...
https://www.jstage.jst.go.jp/article/jphs/118/2/118_11R04FM/_pdf
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Top food sources of Glycine:
http://foodinfo.us/SourcesUnabridged.aspx?Nutr_No=516
"Gelatin is unusually high in the non-essential amino acids glycine and proline"
http://en.wikipedia.org/wiki/Gelatin
(A caveat about gelatin... Never microwave gelatin. Some sources say that microwaved gelatin can have adverse effects on health.)