BACKGROUND:Caffeine is the most widely used pharmacologic substance. Aortic stiffness is an important factor for cardiovascular system performance and a prognosticator of cardiovascular risk. We investigated the effect of caffeine on aortic stiffness in treated hypertensive patients. METHODS:We studied the effect of caffeine (250 mg) in 12 treated hypertensive patients according to a randomized, placebo-controlled, double-blind, cross-over design during a 3-h period. Aortic stiffness was evaluated by carotid-femoral pulse wave velocity. RESULTS:Systolic blood pressure (BP) and pulse pressure increased significantly throughout the study (by 12.3 and 7.4 mm Hg, P =.005 and P <.01, respectively), whereas diastolic BP did not change. Pulse wave velocity increased (by 0.57 m/sec, P <.05) denoting an increase in aortic stiffness. This effect of caffeine lasted throughout the study (3 h), peaking at 60 min and decreasing progressively thereafter. CONCLUSIONS:These results demonstrate, for the first time, that caffeine exerts an acute unfavorable effect on aortic stiffness in treated hypertensive patients. This finding has important implications for the impact of caffeine consumption on cardiovascular risk in hypertension.