A naturalistic investigation of the effects of day-long consumption of tea, coffee and water on alertness, sleep onset and sleep quality |
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Authors: | I Hindmarch U Rigney N Stanley P Quinlan J Rycroft J Lane |
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Institution: | (1) HPRU Medical Research Centre, University of Surrey, Egerton Road, Guildford, Surrey GU2 5XP, UK e-mail: u.rigney@surrey.ac.uk, GB;(2) Unilever Research, Colworth Laboratory, Bedford MK44 1LQ, UK, GB |
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Abstract: | 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 terms of dose and time of consumption. Objectives: This study investigated the effects of day-long consumption of tea, coffee and water on cognitive and psychomotor performance,
and sleep quality at night. Methods: Thirty healthy volunteers received equal volume drinks equivalent to either 1 or 2 cups of tea (containing 37.5 mg or 75
mg caffeine), or coffee (75 mg or 150 mg caffeine), or water, in a randomised five-way crossover design. Drinks were administered
on four occasions during the day (0900, 1300, 1700 and 2300 hours). A psychometric battery consisting of critical flicker
fusion (CFF), choice reaction time (CRT) and subjective sedation (LARS) tests, was administered pre-dose and at frequent time
points post-dose. The Leeds Sleep Evaluation Questionnaire (LSEQ) was completed each morning and a wrist actigraph was worn
for the duration of the study. Results: Caffeinated beverages maintained CFF threshold over the whole day (P<0.05), independent of caffeine dose or beverage type. During the acute phase of beverage ingestion, caffeine significantly
sustained performance compared to water after the first beverage for CFF and subjective sedation (P<0.05), and after the second beverage for the Recognition component of the CRT task (P<0.05). Additionally, there were significant differences between tea and coffee at 75 mg caffeine after the first drink. Compared
to coffee, tea produced a significant increase in CFF threshold between 30 and 90 min post-consumption (P<0.01). However, 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
dependent negative effect on sleep onset (P<0.001), sleep time (P<0.001) and sleep 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 administered repeatedly. This study also demonstrates that day-long
tea consumption 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.
Received: 16 February 1999 / Final version: 20 December 1999 |
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Keywords: | Naturalistic Caffeine Tea Coffee Acute Chronic Cognitive performance Sleep |
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