Effects of Varying Caffeine Dosages and Consumption Timings on Cerebral Vascular and Cognitive Functions: A Diagnostic Ultrasound Study

Caffeine is consumed owing to its stimulatory effects; however, its excessive intake triggers adverse effects. Herein, we analyzed changes in physiological cerebrovascular and cognitive functions following the consumption of 100 and 200 mg of caffeine in healthy adults after 0/30/60 min to ascertain appropriate caffeine consumption habits. The peak systolic velocity (PSV), pulse wave velocity (PWV), and common carotid artery (CCA) diameter were measured using diagnostic ultrasound. Cognitive function was evaluated using the accuracy rate and response time on the two-back task. Percutaneous oxygen saturation (SpO2) and heart rate (HR) were assessed using patient monitoring systems. After consuming 100 mg of caffeine, systolic blood pressure (SBP) increased (p > 0.05) and SpO2 and accuracy rate improved by 30 min (p = 0.018 and p = 0.356) but declined by 60 min (p = 0.924 and p = 0.055). HR and response time continuously decreased (p = 0.209 and p = 0.061, respectively), while PWV showed no change (p > 0.05). After consuming 200 mg of caffeine, SBP (p < 0.05), diastolic blood pressure (p = 0.004 and p = 0.820), and SpO2 (p = 0.002 and p = 0.666) increased significantly, while the accuracy rate (p = 0.634 and p = 0.055, respectively) and response time (p < 0.05) decreased. PWV remained unchanged (p > 0.05). The results revealed distinct dose-dependent patterns on physiological and cognitive changes, with SBP and SpO2 exhibiting greater changes when a higher dose was consumed in a short duration. Although moderate caffeine intake may support vascular health and cognitive function, excessive intake reduces blood flow, alters vascular elasticity, and impairs cognitive activation. These findings highlight the need for guidelines to ensure safe and effective caffeine consumption.