Theanine maintains sleep quality in healthy young women by suppressing the increase in caffeine-induced wakefulness after sleep onset

Energy drinks take advantage of caffeine's effects on wakefulness and performance; however, excessive intake has a negative effect on sleep. Green tea is consumed worldwide and has both a stimulating effect from caffeine and a calming or relaxing effect from theanine. Theanine reduces the excitotoxicity of caffeine. This study evaluated whether theanine improves the sleep quality worsened by caffeine in healthy young women. Sleep latency, sleep time, wake after sleep onset (WASO) time, and the number of WASOs were measured. A crossover study was performed using four treatment groups: theanine (50 mg), caffeine (30 mg), combined theanine and caffeine (TC), and placebo. The sleep stage was determined using electroencephalograms, and cerebral blood flow was measured using near-infrared spectroscopy. The caffeine group showed a significant increase in the WASO time compared with the placebo group; no difference was observed between the theanine or TC group and the placebo group. There were no differences in the sleep-onset latency or number of WASOs between the theanine, caffeine, or TC groups and the placebo group. In combination with theanine, only the caffeine-induced increase in the WASO time was suppressed. Our results suggest that theanine can reduce caffeine's effects on sleep quality.

Automated summary

Energy drinks with excessive caffeine intake have a negative effect on sleep, while green tea, which contains both caffeine and theanine, can improve sleep quality. This study found that theanine can reduce the negative effects of caffeine on sleep by suppressing caffeine-induced wake after sleep onset (WASO) time. However, there were no significant differences in sleep latency or the number of WASOs when comparing theanine, caffeine, or caffeine and theanine combined to a placebo.