THE EFFECTS OF BLACK TEA AND OTHER BEVERAGES ON ASPECTS OF COGNITION AND PSYCHOMOTOR PERFORMANCE

Nineteen healthy volunteers ingested 400 ml black tea, coffee, caffein ated water, decaffeinated tea or plain water on three occasions throug h the day (0900, 1400 and 1900 hours). A 2 x 2 factorial design with c affeine (0, 100 mg) and beverage type (water tea) was employed, with t offee (100 mg caffeine) as a positive internal control, based on a fiv e-way crossover. A psychometric test battery comprising critical flick er fusion (CFF). choice reaction time (CRT), short-term memory (STM) a nd subjective sedation (LARS) was performed at regular intervals throu ghout the day, and intensively so immediately following each beverage. Consumption of tea compared to water was associated with transient im provements in performance (CFF) within 10 min of ingestion and was not affected by the time of day Caffeine ingestion was associated with a rapid (10 min) and persistent reduction in subjective sedation values (LARS), again independent of time of day, but did not acutely alter CF F threshold. Over the whole day, consumption of tea rather than water. and of caffeinated compared to decaffeinated beverages, largely preve nted the steady decline in alertness (LARS) and cognitive capacity obs erved with water ingestion. The effects of tea and coffee were similar on all measures, except that tea consumption was associated with less variation in CFF over the whole day No significant treatment effects were apparent in the data for the STM. Tea ingestion is associated wit h rapid increases in alertness and information processing capacity and tea drinking throughout the day largely prevents the diurnal pattern of performance decrements found with the placebo (no caffeine) conditi on. It appears that the effects of tea and coffee were not entirely du e to caffeine per se: other factors either intrinsic to the beverage ( e.g. sensory attributes or the presence of other biologically active s ubstances) or of a psychological nature (e.g. expectancy) are likely t o play a significant role in mediating the responses observed in this study.