EFFECTS OF CAFFEINE ON BLOOD PRESSURE AND HEART RATE VARIABILITY AT REST AND DURING COLD PRESSOR TEST

Abstract

Objective: Caffeine is the most widely consumed pharmacologically active substance in the world and is found in a variety of foods, and beverages. Even though the acute and long-term effects on the cardiovascular system are widely studied, the accumulated effects of caffeine and physiological stress are not clear. This study aimed to characterize the acute effects of caffeine on blood pressure (BP), heart rate (HR), and heart rate variability (HRV) at rest and during a cold pressor test (CPT) in healthy individuals. Design and method: Nineteen normotensive male participants (25 ± 2 years, BMI 24 ± 3) were enrolled in this double-blinded, placebo-controlled trial. Participants randomly received both a placebo (PL) and a caffeinated (3 mg/kg) drink (CAF) on two separate days. Before and following a 45-minute wash-in period BP, HR, and HRV were measured at supine rest and during a CPT. During the CPT, participants immersed their right hand into cold water (5C) for two minutes. Results: There were no significant differences in resting systolic (130 ± 13 mmHg vs. 125 ± 12 mmHg, p = .187), and diastolic (76 ± 7 mmHg vs. 73 ± 8 mmHg, p = .236) BP, as well as in HR (61 ± 10 bpm vs. 60 ± 8 bpm, p = .531), RMSSD (74 ± 36 ms vs. 83 ± 40 ms, p = .217), and Mean RR (1014 ± 155 ms vs. 1034 ± 140 ms, p = .570) between CAF and PL. The same was true for systolic (152 ± 14 mmHg vs. 151 ± 14 mmHg, p = .785) and diastolic (95 ± 11 mmHg vs. 96 ± 13 mmHg, p = .236) BP during CPT. However, CAF supplementation resulted in a significantly lower HR (62 ± 8 bpm vs. 73 ± 18 bpm, p = .013), and a significantly higher RMSSD (83 ± 51 ms vs. 55 ± 28 ms, p = .004), and Mean RR (1005 ± 158 ms vs. 867 ± 152 ms, p < .001) during CPT compared to PL. Conclusions: The often reported acute increase in BP after caffeine supplementation could not be confirmed in this cohort of normotensive young adults. Caffeine supplementation neither increased nor blunted BP response during the CPT. However, HR was significantly lower, and parasympathetic HRV indices were significantly higher during the CPT after consuming CAF. Thus, caffeine seems to attenuate stress response with a shift in sympathovagal control toward enhanced parasympathetic activity.