Effects of caffeine on pressor regulation during rest and exercise in men at risk for hypertension.

Caffeine-induced blood pressure elevations are well documented in habitual consumers, occurring through both vasoconstrictive and cardiostimulatory actions. Whether caffeine hinders pressor regulation during exercise has been uncertain, particularly in those at risk for hypertension. Thus effects of caffeine versus placebo were studied during supine bicycle exercise in healthy men (ages 20 to 35). Hypertension risk was defined during screening: high risk (HRISK) = 135 to 154/85 to 94 mm Hg plus parental hypertension (n = 20); low risk (LRISK) = less than or equal to 132/84 mm Hg and no parental hypertension (n = 14). Exaggerated pressor responses (greater than or equal to 230/100 mm Hg) seen during exercise after placebo identified a subgroup of seven HRISKs indistinguishable at rest from the remaining HRISK men. This subgroup showed a larger resting diastolic response to caffeine (p less than 0.05) than LRISKs and other HRISKs. Compared with placebo, caffeine increased the number of LRISK (0% to 36%) and HRISK (35% to 50%) men reaching abnormal exercise blood pressures, and blunted normal increments in cardiac index at higher workloads among HRISK men (p = 0.05). Thus restriction of caffeine before exercise might benefit persons with either risk for hypertension or unusual sensitivity to caffeine.