A naturalistic investigation of the effects of day-long consumption of tea, coffee and water on alertness, sleep onset and sleep quality

Rationale: The effects of caffeine, especially caffeinated coffee, on human performance have been extensively studied. However, few studies have been naturalistic representations of how tea/coffee is normally consumed in term s of dose and time of consumption. Objectives: This study investigated the effects of day-long consumption of tea, coffee and water on cognitive and p sychomotor performance, and sleep quality at night. Methods: Thirty healthy volunteers received equal volume drinks equivalent to either 1 or 2 cups o f tea (containing 37.5 mg or 75 mg caffeine), or coffee (75 mg or 150 mg ca ffeine), or water, in a randomised five-way crossover design. Drinks were a dministered on four occasions during the day (0900, 1300, 1700 and 2300 hou rs). A psychometric battery consisting of critical flicker fusion (CFF), ch oice reaction time (CRT) and subjective sedation (LARS) tests, was administ ered pre-dose and at frequent time points post-dose. The Leeds Sleep Evalua tion Questionnaire (LSEQ) was completed each morning and a wrist actigraph was worn for the duration of the study. Results: Caffeinated beverages main tained CFF threshold over the whole day (P<0.05), independent of caffeine d ose or beverage type. During the acute phase of beverage ingestion, caffein e significantly sustained performance compared to water after the first bev erage for CFF and subjective sedation (P<0.05), and after the second bevera ge for the Recognition component of the CRT task (P<0.05). Additionally, th ere were significant differences between tea and coffee at 75 mg caffeine a fter the first drink. Compared to coffee, tea produced a significant increa se in CFF threshold between 30 and 90 min post-consumption (P<0.01). Howeve r, following the second beverage caffeinated coffee at 75 mg significantly improved reaction time (P<0.05), compared to tea at the same dose, for the Recognition component of the CRT task. Caffeinated beverages had a dose dep endent negative effect on sleep onset (P<0.001), sleep time (P<0.001) and s leep quality (P<0.001). Conclusions; These results indicate that ingestion of caffeinated beverages may maintain aspects of cognitive and psychomotor performance throughout the day and evening when caffeinated beverages are a dministered repeatedly. This study also demonstrates that day-long tea cons umption produces similar alerting effects to coffee, despite lower caffeine levels, but is less likely to disrupt sleep. Other differences between tea and coffee were more subtle, and require further investigation.