Acute caffeine administration impaired spatial working memory in habitual coffee/tea drinkers: A randomized, placebo-controlled, double-blind study

Background: Although coffee consumption is widespread worldwide, a recent study showed that acute intake of caffeine negatively affects working memory (WM) performance on n-back tasks among habitual caffeine consumers. However, there is a scarcity of double-blind, placebo-controlled studies that assess the spatial WM (SWM) effects of caffeine using spatial span tasks. Therefore, the present study aimed to examine the effects of acute caffeine administration (200 mg, PO) on SWM and verbal WM (VWM) among habitual caffeine consumers. Methods: The effects of caffeine on working memory (WM) was evaluated through the administration of backward digit span and spatial span tasks under a delay-dependent condition (0, 4, 8, and 6 s) in a randomized, double-blind, placebo-controlled study involving 18 healthy participants. This data is derived from our previous published study. The total scores obtained and the maximum scores achieved were the primary outcome variables of the study. Results: Caffeine had a significant impact on SWM (maximum obtained, p = 0.013; for total scored, p = 0.007) in a delay-independent manner. However, there were no significant main effects of caffeine on VWM (p = 0.82 for maximum obtained, p = 0.56 for total scored). Conclusion: Overall, the present findings contradict the commonly held belief that caffeine improves cognitive performance and suggest that acute administration of caffeine may impair SWM in habitual coffee/tea drinkers. Clinical trial registration number: CT-2018-CTN-02561 (Therapeutic Goods Administration Clinical Trial Registry) and ACTRN12618001292268 (The Australian New Zealand Clinical Trials Registry).