Acute dietary nitrate supplementation attenuates caffeine-induced increase in arterial stiffness in healthy adults: a randomized cross-over trial.

Purpose: Inorganic nitrate (NO3-) supplementation and caffeine have been shown to have conflicting effects on various aspects of cardiovascular function. This study evaluated whether NO3- supplementation would attenuate caffeine-induced cardiovascular strain. Methods: Twenty-four (17 males; age: 24(3) years) healthy participants completed four trials in a randomized, double-blind, placebo-controlled crossover design. The trials were nitrate (NO3-)-rich (400 mg NO3-) and NO3--depleted (92 mg NO3-) beetroot powder consumed, with (BR-CAF and CAF) and without (BR and PL) 6 mg kg-1 caffeine. Brachial and central blood pressure (BP) and arterial stiffness variables were measured pre- and post-supplementation (2.5 h). Macrovascular endothelial function was assessed post-supplementation using flow mediated dilation (FMD). Results: Arterial stiffness measures of augmentation pressure (mmHg) and index (%) were higher following CAF (+3(2) mmHg and 10(9)%) than PL (+1(3) mmHg and +4(11)%) and BR (+0(3) mmHg and +1(11)%; P < 0.001-0.007), with no difference between BR-CAF (+1(3) mmHg and +3(10)%) and PL or BR (P = 0.505-0.689). Brachial BP, central BP and macrovascular endothelial function were not altered with BR or CAF compared to PL (P = 0.067-0.359). Plasma [nitrite] was higher in BR and BR-CAF than PL and CAF (P < 0.001). There were no between-group differences in plasma [cyclic guanosine monophosphate] (P = 0.370). Conclusion: Acute NO3- supplementation offset caffeine-induced increases in arterial stiffness variables. These findings improve our understanding of the cardiovascular health benefits afforded by acute NO3- consumption under cardiovascular strain.