“Does Caffeine Intake Enhance Absolute Levels of Cognitive Performance?”, 1993 ():
The relationship between habitual coffee and tea consumption and cognitive performance was examined using data from a cross-sectional survey of a representative sample of 9,003 British adults (the Health and Lifestyle Survey).
Subjects completed tests of simple reaction time, choice reaction time, incidental verbal memory, and visuo-spatial reasoning, in addition to providing self-reports of usual coffee and tea intake. After controlling extensively for potential confounding variables:
a dose-response trend to improved performance with higher levels of coffee consumption was observed for all 4 tests (p < 0.001 in each case). Similar but weaker associations were found for tea consumption, which were statistically-significant for simple reaction time (p = 0.02) and visuo-spatial reasoning (p = 0.013). Estimated overall caffeine consumption showed a dose-response relationship to improved cognitive performance (p < 0.001 for each cognitive test, after controlling for confounders). Older people appeared to be more susceptible to the performance-improving effects of caffeine than were younger.
The results suggest that tolerance to the performance-enhancing effects of caffeine, if it occurs at all, is incomplete.
[Keywords: caffeine, cognitive performance, coffee, tea]