Effects of Nitrate Supplementation on Cardiovascular and Autonomic Reactivity in African-American Females

Abstract

Previous studies have shown that beetroot juice (BJ) decreases systolic blood pressure (SBP) and oxygen demand. This study tests the hypothesis that a beetroot juice (BJ) treatment increases heart rate variability (HRV) measured by the average standard deviation of normal-normal electrocardiogram RR intervals (SDNN) and the low frequency (LF), mainly sympathetic, fast Fourier transform spectral index of HRV. The subjects were 13 healthy young adult African-American females. Placebo control orange juice (OJ) and BJ treatments were given on separate days. Blood nitric oxide [NO], SBP and RR intervals were measured at rest and at constant workloads set to 40% and 80% of the predetermined VO2peak. Two hours after ingestion the BJ treatment increased [NO] and decreased SBP. BJ also increased SDNN at rest and at the 40% VO2peak workload, without significant effects on LF. SDNN was significantly greater after the BJ than after the OJ treatment, across the two physical activity conditions and SDNN was (negatively) correlated with SBP. These results suggest that BJ decreases SBP and increases HRV at rest and during aerobic exercise. Similar results in subjects with prehypertension or hypertension could translate to a dietary nitrate treatment for hypertension.

Dietary nitrate improves muscle microvascular reactivity and lowers blood pressure at rest and during isometric exercise in untreated hypertensives

“…This effect was evident from the 1 st min of isometric exercise and was accompanied by a smaller rise in TPR. These results concur with previous studies reporting an attenuated BP and total vascular resistance response after dietary ingestion during dynamic (aerobic) exercise . This is of practical importance, as dynamic exercise (treadmill/cycle ergometer) may be difficult for individuals with mobility limitations (e.g., orthopedic conditions).…”

“…The attenuated increase in TPR during isometric handgrip after nitrate‐rich BRJ ingestion was not accompanied by changes in cBRS or reductions in CO. Based on these findings, it is likely that the blunted BP response in hypertensives during isometric exercise after ingestion is, at least in part, a consequence of attenuation in the hypersensitivity of the exercise pressor reflex, and thus a reduction in peripheral resistance, and of an improvement in muscle microvascular function . In support, previous studies showed that the augmented exercise BP response is related to increases in peripheral vasoconstriction and that in healthy humans, acute BRJ ingestion decreases muscle sympathetic outflow during a 2‐min isometric handgrip and attenuates sympathetic signaling during aerobic exercise . Also, in a recent study, the rise in BP during isometric handgrip in hypertensives was inversely correlated with microvascular reactivity, suggesting an involvement of small vessel stiffness to the exaggerated exercise BP response in this population …”

“…One of the reasons is the concern of an exaggerated BP response during isometric exercise in hypertensives, which may result to early discontinuation of exercise. Although BRJ consumption has well documented BP‐lowering effect during aerobic exercise in healthy and pre‐hypertensives, no study has examined its efficacy on reducing BP responsiveness to isometric physical stress in newly diagnosed untreated hypertensives.…”

Mechanisms underlying blood pressure reduction by dietary inorganic nitrate

“…Human sympathetic vasoconstrictor traffic and blood pressure elevation were found to be counteracted by increased release of NO (indirectly measured as nitrate/nitrite) in healthy young males . In female African Americans, dietary nitrate can modulate cardiovascular function (heart rate variability) and autonomic reactivity, and the authors propose that similar results in subjects with prehypertension or hypertension could translate to a dietary nitrate treatment for hypertension. Moreover, another study in young male adults showed that short‐term nitrate supplementation (450 mg/day; 3 days) augmented reflex cutaneous vasodilation and reduced blood pressure during heat stress, but not during baseline conditions …”

The benefits and risks of beetroot juice consumption: a systematic review

“…These results indicate that BRJ can decrease the cardiac afterload and myocardial oxygen demand at rest and at submaximal levels of aerobic exercise . However one study with African-American females did show a significantly lower heart rate after ingestion of BRJ (Bond, Curry, Adams, Asadi, et al 2014).…”