Abstract P298: Normotensive Habitual Caffeine Consumers Experience No Change in Blood Pressure or Pulse Wave Velocity Following the Combined Consumption of Caffeine and Dietary Nitrate
Authors: Fair Haley M , Waller Justin D , Marshall Kennedy , Olzer Valerie J , Smoliga James M , Carriker Colin R 
Published: March 2019

Intro:
Caffeine intake may elevate blood pressure (BP), while habitual consumption leads to developed tolerance, providing conflicting evidence for incurred changes in BP. Dietary nitrate consumption decreases BP and reduces arterial stiffness in patients with atherosclerosis and hypertension due to increased plasma nitrite and enhanced bioavailability of nitric oxide. However, a decline in BP for a healthy cohort could be an unwanted side effect for normotensive individuals. Less is known about the combined effects of dietary nitrate and caffeine on resting hemodynamics in a healthy population.

Hypothesis:
We hypothesized that caffeine supplementation would increase systolic blood pressure (SBP) and pulse wave velocity (PWV) while combined dietary nitrate consumption would attenuate this rise.

Methods:
In a randomized, double-blind, counterbalanced study, eight healthy, young adults who typically consumed some but not more than 500 mg caffeine/day completed 4 separate visits to the laboratory, each visit separated by one week. Prior to each visit, participants consumed a 4-day supplementation regimen of either dietary nitrate (12.4 mmol, NIT) or a placebo nitrate (PLN) combined with either caffeine (3 mg/kg, CAF) or placebo caffeine (PLC); this comprised 1 of 4 treatments. The final dose of NIT or PLN was consumed 2.5 hours prior to assessments while CAF or PLC was consumed 1 hour prior. Participants minimized consumption of dietary nitrate rich foods and caffeine during the 4 days leading up to their scheduled visit. Each visit consisted of measurements of peripheral SBP and diastolic blood pressure (DBP) with aortic central systolic and diastolic blood pressure (cSBP and cDBP, respectively) assessed noninvasively using pulse wave analysis. Measurement of arterial stiffness via applanation tonometry determined PWV. A linear mixed effects model analysis was performed to determine if supplementation regimen influenced hemodynamic parameters.

Results:
SBP of NIT+CAF (115±6 mmHg), PLN+CAF (117±9 mmHg), NIT+PLC (115±6 mmHg) and PLN+PLC (115±6 mmHg)(p=0.591) and PWV of NIT+CAF (5.5±1.1 m/s), PLN+CAF (5.8±0.7 m/s), NIT+PLC (5.8±0.6 m/s) and PLN+PLC (5.6±1.0 m/s) (p=0.353) were not statistically different between treatments. In addition, DBP (p=0.496), cSBP (p=0.656), cDBP (p=0.548), aortic augmentation index (p=0.054), and resting heart rate (p=0.646) were not different between treatments.

Conclusion:
Following 4 days of caffeine supplementation, habitual caffeine users did not experience any changes in resting hemodynamics when compared to a placebo supplement. In addition, dietary nitrate did not incur any changes in resting metrics whether or not it was consumed alongside caffeine. In this regard, habitual caffeine users are not affected by 3mg/kg doses of caffeine, and dietary nitrate (12.4 mmol/day) does not further reduce the BP of healthy normotensive adults.