Abstract
To investigate the effects of L-serine intake on human sleep, we conducted two randomized double-blinded crossover studies. In Study 1, healthy subjects who were dissatisfied with their sleep were given L-serine or a placebo 30 min before going to bed. After waking the next morning, subjective sleep quality was rated using the Ogri-Shirakawa-Azumi subjective sleep rating scale. In Study 2, subjective sleep quality was rated using the St. Mary’s Hospital sleep questionnaire, and objective parameters, including sleep initiation time, number of nighttime awakenings, and hours of sleep, were evaluated using actigraphy. In Study 1, factors related to “sleep initiation” and “sleep maintenance” during the L-serine intake period were significantly improved compared to the placebo intake period (p = 0.02 and p = 0.008, respectively). In Study 2, scores for “How well did you sleep last night?” and “How satisfied were you with last night’s sleep?” were significantly better during L-serine intake compared to placebo (p = 0.04 and p = 0.03, respectively). Subjective evaluation of sleep quality on waking was thus improved. In addition, objective evaluation using actigraphy showed that the “number of nighttime awakenings” tended to be decreased (p = 0.08). These findings suggest that intake of L-serine before going to bed may improve human sleep.
Highlights
Sleep is a basic life process that greatly affects human health
The “sleep maintenance” (L-serine, 24.9 vs. placebo, 22.8; p = 0.02) and “sleep initiation” (L-serine, 26.9 vs. placebo, 24.7; p = 0.008) factor scores were significantly better during L-serine intake compared with placebo (Figure 1)
Scores for question “How well did you sleep last night?” (p = 0.04) and question “How satisfied were you with last night’s sleep?” (p = 0.03) were significantly better during L-serine intake compared with placebo
Summary
Sleep is a basic life process that greatly affects human health. The effects of sleep disturbance or deprivation on the brain, mind and body include hypobulia and depression, and effects potentially leading to hypertension and obesity (Gangwisch et al 2005), impairing human quality of life. We conducted two studies to clarify the effects on human sleep of L-serine intake before going to bed. Subjects were not permitted to drink alcohol, stay out overnight, or use any medications or supplements that would affect sleep. They were instructed to maintain their usual eating and lifestyle habits. Each night for 4 consecutive days, 30 min before going to bed, the subjects ingested 3 g of L-serine powder (content: ≥98.5%) or a placebo powder (trehalose). At night on 2 consecutive days, 30 min before going to bed, the subjects ingested 3 g of L-serine powder or a placebo powder. The statistical analyses were performed using the statistical software program StatView for windows version 5.0 (SAS Institute., North Carolina)
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