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Hindmarch I, Quinlan PT, Moore KL, Parkin C. 
“The effects of black tea and other beverages on aspects of cognition and psychomotor performance”. 
Psychopharmacology Berl. 1998 Oct 28;139(3):230-8.
Nineteen healthy volunteers ingested 400 ml black tea, coffee, caffeinated water, decaffeinated tea or plain water on three occasions through the day 0900, 1400 and 1900 hours. A 2 x 2 factorial design with caffeine 0, 100 mg and beverage type water, tea was employed, with coffee 100 mg caffeine as a positive internal control, based on a five-way crossover. A psychometric test battery comprising critical flicker fusion CFF, choice reaction time CRT, short-term memory STM and subjective sedation LARS was performed at regular intervals throughout the day, and intensively so immediately following each beverage. Consumption of tea compared to water was associated with transient improvements 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 CFF threshold. Over the whole day, consumption of tea rather than water, and of caffeinated compared to decaffeinated beverages, largely prevented the steady decline in alertness LARS and cognitive capacity observed 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 with 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 condition. It appears that the effects of tea and coffee were not entirely due to caffeine per se other factors either intrinsic to the beverage e.g. sensory attributes or the presence of other biologically active substances or of a psychological nature e.g. expectancy are likely to play a significant role in mediating the responses observed in this study.
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