Cardiovascular Effects of Caffeine and Stress in Regular Coffee Drinkers

The effects of caffeine on cardiovascular activity at rest and in response to psychological stress were studied in a group of 30 healthy males who were regular coffee drinkers to replicate caffeine‐stress interactions found previously in caffeine‐naive subjects. Measures of heart rate, blood pressure, and forearm blood flow were recorded at rest and during the performance of a stressful mental task in two separate sessions. Caffeine (250 mg) or placebo was administered double‐blind in a within‐subject design. Relative to placebo, caffeine had a pressor effect at rest which persisted during stress and recovery such that blood pressure during stress was higher if caffeine had been consumed. Caffeine also magnified the forearm blood flow and forearm vascular resistance responses to stress, suggestive of a synergistic interaction of caffeine and stress. Analysis of individual difference variables suggested that caffeine effects on the forearm vascular variables were greatest in subjects who were Type B and had a positive family history of hypertension. Results suggest that regular caffeine use does not necessarily lead to tolerance for caffeine‐stress interactions and that certain characteristics may be associated with greater sensitivity to caffeine's effects.