Fifteen days of drinking 70 ml of beetroot juice per day was associated with increases in blood levels of nitrates and nitrites, and decreases in systolic and diastolic blood pressure, compared to consuming the same amount of a nitrate-free beetroot juice, according to findings published in the American Journal of Physiology - Regulatory, Integrative and Comparative Physiology .
“These findings suggest that beetroot juice can act as a dietary ergogenic supplement capable of enhancing oxygen delivery and reducing work of the heart, allowing exercise to be performed at a given workload for a longer period of time before the onset of fatigue,” wrote scientists from Kyung Hee University in Korea and the University of California at Davis.
“Beetroot juice supplementation may also represent an alternative, more natural intervention for individuals that suffer from reductions in functional capacity and exercise tolerance related to cardiovascular diseases such as hypertension, heart failure and cardiovascular ischemia.”
There has been increasing levels of interest in the potential benefits of beetroot juice for boosting athletic performance, particularly following a report in the Wall Street Journal that stated that the Auburn University football team drinks the juice before its games.
The majority of the science has been in support of the potential sports nutrition benefits of beetroot, linked to the nitrate concentration in the vegetable.
The scientists behind the new study sought to examine if chronic consumption of beetroot juice could affect cardiovascular health and impact exercise in 14 healthy men with an average age of 21. The men were randomly assigned to receive 70 ml per day of beetroot juice or the same volume of nitrate-depleted beetroot juice for 15 days in a double-blind, crossover trial. A two week washout period followed the first intervention phase before the participants were crossed over to the other group.
Results showed that beetroot juice consumption was associated with significant reduction in systolic and diastolic blood pressure, compared with the control (nitrate-depleted juice) group and compared to pre-supplementation values for all levels of exercise workload (30%, 60%, and 80% of VO2peak).
Reductions were also recorded for MAP (mean arterial pressure) and TPR (total peripheral resistance; a measure of blood flow).
“[O]ur results indicate that effects of an acute dose of [nitrates] on cardiovascular function during exercise can not only be maintained via dietary supplementation with a smaller dose but also can be extended such that cardiac function (i.e., stroke volume and cardiac output) is enhanced and afterload on the heart is reduced further (i.e., reductions in DBP and MAP),” wrote the researchers.
Endothelial function, as measured by flow mediated dilation (FMD), also improved post-supplementation by over 5%, compared to pre-supplementation, added the researchers.
“Compared to acute effects of beetroot juice, the relevance of our results relates to the ability of nitrates to act chronically as a dietary nutraceutical that is capable of maintaining or enhancing its acute effects on oxygen delivery at a given level of exercise, while also causing reductions in blood pressure and work of the heart,” they wrote.
“Consequently, the onset of fatigue may be delayed in healthy individuals and athletes, allowing for exercise to be performed for longer periods of time.
“These effects of chronic dietary supplementation with nitrates also have clinical implications,” they added. “It is well known that functional capacity and exercise tolerance are reduced in pathological conditions such as hypertension, heart failure, coronary heart disease and diabetes, which can limit the ability to perform work and participate in activities of daily life. Since such limitations are related to endothelial dysfunction, increases in vascular resistance and reductions in skeletal muscle blood flow, regular treatment with dietary nitrates may at least partially offset these debilitating effects.”
Source: American Journal of Physiology - Regulatory, Integrative and Comparative Physiology
Published online ahead of print, doi: 10.1152/ajpregu.00099.2015
“Effects of Chronic Dietary Nitrate Supplementation on the Hemodynamic Response to Dynamic Exercise”
Authors: J-S. Lee, C.L. Stebbins, E. Jung, H. Nho, J-K. Kim, M-J. Chang, H-M. Choi