Nitrate-rich Beetroot Supplementation Improves Endothelial Function And Attenuates Cardiovascular Strain Following Acute Caffeine Ingestion.

PURPOSE: High doses of caffeine have been shown to increase brachial and central blood pressure (BP) and may also adversely impact pulse wave variables and endothelial function. Dietary nitrate (NO3-) has been reported to positively modulate various aspects of cardiovascular function. The purpose of the current study was to investigate whether dietary NO3- supplementation blunts the acute perturbations to cardiovascular function after caffeine ingestion. METHODS: Twenty-four healthy participants (17 males, 7 females; mean ± SD: age 24 ± 3 yr, BMI 24 ± 3 kg/m2, systolic BP 109 ± 10 mmHg) completed four experimental trials in a double-blind, randomized, crossover design. The experimental conditions were 400 mg NO3--rich or NO3- -depleted beetroot powder, with (BR-CAF and CAF) and without (BR and PL) 6 mg/kg caffeine, respectively. During each trial, brachial and central BP, and pulse wave variables were measured pre- and post-supplementation with flow mediated dilation (FMD) measured post-supplementation. Data were assessed using linear mixed models, with Holm Bonferroni post-hoc analysis. RESULTS: There were significant time*condition interaction effects for augmentation index (AiX), AiX normalised to heart rate (AiX@75HR), and augmentation pressure (AP; P ≤ 0.02), but not brachial or central BP variables (P > 0.05). Compared to PL, pulse wave variables were increased in CAF (AiX +7%, AiX@75HR +9%, AP +1%; P < 0.021), but not BR (AiX -2%, AiX@75HR -3%, AP 0%; P > 0.05). There were significant main effects for condition for FMD normalised to shear rate (P < 0.001), with FMD increased following BR (+0.003 %/s-1) and BR-CAF (+0.002 %/s-1; P < 0.001) compared to PL. FMD was also greater in BR-CAF compared to CAF (+0.003 %/s-1; P < 0.001) with no differences between CAF and PL (0.001 and 0.002 respectively; P > 0.05). CONCLUSION: Acute caffeine ingestion adversely impacted pulse wave variables with these effects offset by NO3- supplementation. Acute NO3- supplementation increased FMD and this effect was not diminished by caffeine ingestion. These findings suggest that acute NO3- ingestion can improve endothelial function and attenuate aspects of the cardiovascular strain elicited by caffeine ingestion, which supports the notion of a potential cardioprotective effect of increased dietary NO3- intake.