Effects of coffee on cardiovascular responses to stress: a 14-week controlled trial

We studied the cardiovascular responses to orthostatic and mental stress of 43 healthy subjects who daily received six cups of boiled or filtered coffee and of 21 healthy subjects who abstained from caffeine-containing beverages. All 64 subjects first received six cups of filtered coffee/day for 2 weeks. Then blood pressure (BP) and heart rate (HR) were recorded before, during, and after a "stand upright" test and a mental arithmetic test. Subjects were then randomized to either complete abstinence from caffeine-containing beverages (n = 21), or consumption of six cups of filtered coffee (n = 21), or consumption of six cups of boiled coffee/day (n = 22). The stress tests were repeated after subjects had been on these regimens for 8 weeks. Abstinence from coffee did not affect the responses of BP or HR to orthostatic stress, or the response of BP to mental stress. The increase in HR caused by mental stress was five beats/min less (p = 0.02) in the no-coffee group than in the filtered- (95% confidence interval -8.8 to -1.2) or boiled- (95% confidence interval -8.4 to -0.8) coffee group. It is concluded that elimination of caffeine decreases the HR response to mental stress.