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Three recently published controlled clinical trials all indicate favorable effects of beetroot juice (BRJ) on exercise-related outcomes. The first of these, found in the European Respiratory Journal, evaluated the use of BRJ by people with chronic obstructive pulmonary disease (COPD) who also had hypertension. This randomized and placebo-controlled double-blinded trial enrolled 81 participants, 70 of whom completed the 3-month trial, with half receiving a single daily dose of 70mL BRJ containing 400mg nitrate (NO3−), and half receiving a taste and color-matched placebo depleted of nitrate. The primary endpoint, systolic blood pressure, dropped significantly (-4.5 mmHg) compared to placebo, as did the mean arterial pressure. A meaningful improvement in exercise capacity was also observed, marked by a 30 m increase in the 6-minute walk test. Measures of endothelial function and vascular stiffness (reactive hyperemia index and the augmentation index, respectively) also improved with BRJ versus placebo. COPD is characterized by a limited exercise capacity and often by hypertension. This encouraging study follows a previously published ON-EPIC (Oral Nitrate to Enhance Pulmonary rehabilitation In COPD) controlled trial that demonstrated significant improvements in exercise capacity and systolic blood pressure with BRJ supplementation, at a dose of 800 mg nitrate per day.
The second study was a small but triple-blinded and controlled cross-over trial, published in Free Radical Biology & Medicine. Fourteen physically inactive postmenopausal women with hypertension performed submaximal aerobic exercise 2.5 hours following either placebo or BRJ (800 mg nitrate), and also had an exercise session following 6 days of either daily placebo or BRJ (400 mg nitrate) supplementation, allowing for measurement of acute as well as short-term changes associated with BRJ as they relate to exercise.
The single dose of BRJ was associated with a significant drop in systolic blood pressure compared to placebo (-9.28 mmHg) as well as improved flow-mediated dilation (FMD, a sign of nitric oxide-induced vasodilation). FMD was also improved after 1 week of BRJ supplementation both before and after exercise. A more rapid return to parasympathetic nervous activity following exercise, marked by an increase in heart rate variability, was also observed with BRJ supplementation. While a small study, this faster return to parasympathetic reactivation may be a sign of greater aerobic fitness.
The third trial, published in the Journal of the International Society of Sports Nutrition, was a randomized and double-blinded placebo-controlled crossover trial that evaluated the acute effects of 2 different doses of BRJ on multiple exercise-related parameters in 13 young normotensive women (mean age ~23 years old) engaging in at least 150 minutes moderate activity per week. Each woman received either a placebo, BRJ with 400 mg nitrate, or BRJ with 800 mg nitrate, and 2.5 hours later (at maximum nitric oxide levels), performed a high-intensity interval exercise (8 cycles of cycling at 85% of peak power output for 1 minute and 20% of peak power output for 1 minute).
Although no additional benefit was observed with higher doses, women who had taken either dose of BRJ had significant reductions in their mean heart rate as well as their rate of perceived exertion during the interval training, during their recovery periods, and throughout the entire protocol. No difference in blood pressure was observed between treatments, though all women were normotensive at the study onset. Similarly, no difference was observed in blood glucose or lactate between treatments in this normoglycemic group (women with diabetes were excluded, and the mean baseline glucose was 95 mg/dL). The results of this study were generally consistent with the gains in high-intensity exercise performance and reduction in mean heart rate among trained male soccer players observed in a randomized trial using BRJ with 800 mg nitrate over a 1 week period, though it suggests that at least in this population, 400 mg nitrate may be a saturating dose.
While these studies have very small sample sizes, they do suggest a potential for benefit across a wide range of people, from young and physically active adults to older and inactive adults. Additionally, the reduction in blood pressure among women with hypertension and study participants with COPD and hypertension (but not normotensive women) points to a risk reduction in cardiovascular disease along with a boost in exercise-related parameters. The obvious mechanism is the increase in nitric oxide which occurs following BRJ supplementation. BRJ has been shown to effectively increase plasma nitrate concentrations in both men and women, and the subsequent increase in vasodilation may partially explain the observed benefits (likely to be greater in people with low dietary nitrate intake). However, this may not be the whole story; an experimental model suggests that BRJ may also potentiate cardiac contractility by modulating the expression of cardiomyocyte calcium-handling proteins, subsequently increasing transient calcium concentrations and left ventricular contractile function. Human trials have shown that dietary nitrate also affects skeletal muscle contractility, and a systematic review concluded that it appears to improve explosive exercise performance, perhaps especially in fatiguing muscles. Hopefully, future studies will help clarify precise benefits and optimal dosing, especially over longer periods of administration.
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