Cardiorespiratory function associated with dietary nitrate supplementation

Abstract

The advent of medical nutrition therapy and nutritional physiology affords the opportunity to link diet to specific cardiovascular mechanisms, suggesting novel treatments for cardiovascular disease. This study tests the hypothesis that beetroot juice increases the plasma nitric oxide (NO) concentration, which is associated with improvements in cardiorespiratory function at rest and during submaximal aerobic exercise. The subjects were 12 healthy, young adult, normotensive African-American females, with a body mass of 61 ± 2 kg, body fat of 28% ± 4%, and peak oxygen consumption of 26 ± 3 mL·kg(-1)·min(-1). The subjects were studied at rest and during cycle ergometer exercise at 40%, 60%, and 80% of peak oxygen consumption. Plasma NO concentration, respiratory quotient (RQ), minute ventilation, systolic and diastolic blood pressure (SBP and DBP), heart rate, and oxygen consumption were compared between isocaloric, isovolumetric placebo control orange juice and experimental beetroot juice treatments on separate days. The beetroot juice treatment increased plasma NO concentration and decreased oxygen consumption, SBP, and the heart rate-SBP product at rest and at 40%, 60%, and 80% of peak oxygen consumption in the absence of significant effects on RQ, minute ventilation, heart rate, and DBP. These findings suggest that, in healthy subjects, beetroot juice treatments increase plasma NO concentration and decrease cardiac afterload and myocardial oxygen demand at rest and during 3 submaximal levels of aerobic exercise. Future studies should determine the cellular and molecular mechanisms responsible for the improvement in cardiorespiratory function associated with dietary nitrate supplementation and whether they translate into better cardiovascular function and exercise tolerance in individuals with a compromised cardiovascular system.

Fig. 1

Effects of beetroot juice treatment on plasma nitric oxide. Left panel: Bars represent individual subject values of plasma nitric oxide concentrations, expressed in nmol·L⁻¹, for a placebo control orange juice treatment and an isocaloric, isovolumetric beetroot juice treatment on separate days in 12 healthy, normotensive, young adult, African-American, female university students. The individual values for the 12 subjects are depicted as sequential bars for each treatment. *, Difference between the mean ± SD placebo control orange juice treatment (4.5 ± 3.4 nmol·L⁻¹) and the beetroot juice treatment (17.8 ± 8.8 nmol·L⁻¹) was statistically significant at p < 0.001.

Fig. 2

Effects of beetroot juice treatment on the rate-pressure product. Bars represent means ± SD of the heart rate × systolic blood pressure product, expressed in beats·min⁻¹·mm Hg⁻¹ × 10⁻⁴, for a placebo control orange juice treatment and an isocaloric, isovolumetric beetroot juice treatment on separate days in 12 normotensive, young adult, African-American, female university students. The treatments are compared at rest (baseline) and at constant workload power outputs corresponding to 3 submaximal levels of aerobic exercise (40%, 60%, and 80% of each subject’s predetermined peak oxygen consumption (V̇O_2peak)). *, Difference between the control and beetroot juice treatments was statistically significant at p < 0.01.

Fig. 3

Effects of beetroot juice treatment on oxygen consumption. Bars represent means ± SD of oxygen consumption, expressed in mL·kg⁻¹·min⁻¹, for a placebo control orange juice treatment and an isocaloric, isovolumetric beetroot juice treatment on separate days in 12 normotensive, young adult, African-American, female university students. The treatments are compared at rest (baseline) and at constant workload power outputs corresponding to 3 submaximal levels of aerobic exercise (40%, 60%, and 80% of each subject’s predetermined peak oxygen consumption (V̇O_2peak)).*, Difference between the control and beetroot juice treatments was statistically significant at p < 0.05.