Should Coffee Consumers Not Have Their Habitual Morning Coffee Before Testing Their Cognitive Functions?

OBJECTIVE: Caffeine could improve cognitive functions, but study protocols usually prohibit drinking coffee before cognitive testing. However, regular coffee consumers may experience withdrawal effects when they cannot drink their habitual coffee, which may impair cognitive performance. Therefore, we tested the effects of overnight coffee abstinence in regular coffee consumers: once allowing to drink their coffee and once not drinking coffee. The cognitive performance was compared with non-regular coffee consumers. METHODS: Thirty regular coffee consumers (RCCs) and 25 non-regular consumers (N-RCCs) took part in this study. RCCs were tested after their habitual morning coffee (c-RCC) and after overnight abstinence (a-RCC); N-RCCs were tested once. A cognitive battery assessed reaction time (RT), processing speed (digit symbol substitution test), working memory, verbal learning/memory and executive function (Stroop). Sleep quality was included as a covariate. RESULTS: Compared to c-RCC, overnight coffee abstinence significantly slowed RTs but did not affect the performance in the other cognitive tasks. In the a-RCC condition, but not the c-RCC condition, the RTs were slower than those of the N-RCCs, while accuracy measures were comparable across groups. Sleep quality did not alter these findings. CONCLUSIONS: Overnight coffee abstinence selectively slowed RT, and no statistical support was found for effects on memory or executive function. This suggests that overnight coffee abstinence protocols may introduce withdrawal-related RT slowing as a confound in habitual consumers, whereas other cognitive domains may not be affected. Allowing habitual consumers to maintain normal coffee intake could reduce this bias, supporting tailored rather than uniform abstinence requirements based on the specific outcomes studied.