Caffeine, Stress, and the Cardiovascular System: The Influence of Autonomic Regulatory Capacity

Abstract

Caffeine is the most widely consumed stimulant in the world and has the biological potential to adversely influence cardiovascular health. In particular, caffeine consumption acutely increases blood pressure at rest and in times of stress. Despite this, epidemiological research has yet to ascertain if caffeine consumption may contribute to the development of cardiovascular disease. As such there is a need for further research into the aetiology of caffeine‘s effects on the cardiovascular system. In a randomised, placebo-controlled, crossover experiment, the present study assessed the cardiovascular and emotional responses of 20 participants (n = 10 males) in order to examine the effects of caffeine when responding to an orthostatic challenge and a stressful speech task. In a novel approach within caffeine research, the underlying autonomic regulatory capacity of the participants was indexed by resting heart rate variability (HRV). Results indicated that at rest, caffeine exerted a significant increase on the blood pressure of participants with high, but not low, resting HRV. This suggests that individuals with higher autonomic flexibility are more responsive to the pharmacological challenge of caffeine. Furthermore, caffeine enhanced cardiovascular responsivity (potentiated blood pressure and heart rate) to acute psychological, but not physical, stress. This was related to the counterbalancing of the caffeine and placebo conditions such that only participants who ingested caffeine in the first experimental session exhibited potentiated cardiovascular responsivity to the psychological stressor. Together, this was taken to suggest that caffeine may exert a significant effect on top-down regulation of autonomic output. In addition, the emotional experience of the participants was not related to the enhanced cardiovascular responsivity under the influence of caffeine, suggesting a disconnection between the physiological and emotional experience of the participants. Overall, the findings suggest that autonomic regulatory capacity may represent an inter-individual difference that predicts differential cardiovascular responsivity to caffeine consumption. Furthermore, that caffeine potentiated cardiovascular responsivity to psychological stress may have implications for the development of chronic cardiovascular disease or the initiation of acute cardiac events. Elaboration of the effects of autonomic regulatory capacity on cardiovascular responsivity to stress is proposed as a pertinent area for future research.