Can glycine improve sleep or reduce nighttime urinary frequency?

Answer:

Glycine is a non-essential amino acid (meaning that it can be made in the body and is not required from the diet) that acts as a neurotransmitter.

Several small clinical trials (generally supported by Ajinomoto, which sells glycine) have evaluated the effects of glycine supplementation for improving sleep and for reducing nighttime urinary frequency in people with overactive bladder, chronic prostatitis, and/or bladder pain syndrome/interstitial cystitis.

Health benefits of glycine

Sleep and fatigue
A study among eleven men and women with self-reported "unsatisfactory sleep," found that 3 grams of glycine taken one hour before bedtime significantly improved self-reported sleep quality and shortened the time it took to fall asleep (as measured by brain wave, heart rate and breathing monitors) compared to placebo (Yamadera, Sleep Biologic Rhythms 2007). Two other very small studies, each conducted among 10 to 15 Ajinomoto employees, found that 3 grams of glycine taken one hour before bedtime improved self-reported sleep quality and/or decreased next-day fatigue (Inagawa, Sleep Biologic Rhythms 2006; Bannai, Front Neurol 2012). No adverse events were reported.

Overactive bladder and chronic prostatitis
A study in Japan among 16 men and four women (average age 67) with mild to moderate overactive bladder, chronic prostatitis and/or bladder pain syndrome/interstitial cystitis found that 3 grams of glycine taken twice daily for one month modestly reduced nighttime urinary urgency and frequency (but not during the day), and slightly improved overall scores on an assessment of overactive bladder symptoms (a decrease of about 1 point on a 15-point scale) and self-reported "vitality" compared to placebo. In addition, glycine supplementation slightly reduced the amount of time it took to fall asleep and modestly decreased bladder pain as well as and systolic and diastolic blood pressure compared to baseline, but these improvements were not statistically significant compared to placebo (Sugaya, J Complement Integr Med 2021).

Glycine safety, side effects, and drug interactions

There are no known side effects of glycine when taken at the doses used in these studies, or in doses of up to 60 grams/day for up to six weeks (Javitt, Int J Neuropsychopharmacol 2001).

Be aware that glycine might potentially worsen symptoms in some people with schizophrenia taking antipsychotic medication clozapine (Clozaril) (Potkin, Am J Psychiatry 1999).