The research team conducted their study with eight men aged between 19 and 38. They were given 500ml per day of organic beetroot juice for six consecutive days before completing a series of tests, involving cycling on an exercise bike. On another occasion, they were given a placebo of blackcurrant cordial for six consecutive days before completing the same cycling tests.
After drinking beetroot juice the group was able to cycle for an average of 11.25 minutes, which is 92 seconds longer than when they were given the placebo. This would translate into an approximate 2% reduction in the time taken to cover a set distance. The group that had consumed the beetroot juice also had lower resting blood pressure.
The findings, published on Friday in the US-based Journal of Applied Physiology, will be of keen interest to endurance athletes but may also prove helpful to people with cardiovascular, respiratory or metabolic diseases as well as the elderly, the researchers said.
There are essentially two ways to enhance physical performance in relation to oxygen intake.
One is to raise the “VO2-max” level, which is an individual’s highest possible rate of oxygen consumption during all-out exercise.
The V02-max ceiling varies from person to person. It is partly genetic but it can be increased through training or the use of EPO, the oxygen-boosting drug that has plagued the Tour de France cycling competition as well as other professional sports.
“But there is an alternative,” explained Andy Jones, a professor at the University of Exeter in Britain and lead author of the study.
“If you can reduce the energy cost” – the amount of oxygen used – “that can be beneficial too,” he told AFP by phone.
That’s where beetroots come in.
In experiments, Jones and colleagues asked two groups of people to exercise at a fixed, high-intensity work rate for as long as they possibly could.
The group that drank a red-coloured placebo held out on average for nine or ten minutes. Those who drank beetroot, however, went 11 or 12 minutes.
“They were exercising at exactly the same work rate. The improvement in performance was not because the V02-max had changed but simply because the efficiency had been enhanced,” Jones said.
“We were amazed by the effects on oxygen uptake because these effects cannot be achieved by any other known means.”
Whether the juice will also work over several hours of less intense exercise – equivalent to long-distance running or cycling – remains to be shown but seems likely, Jones added.
The researchers are not sure exactly how the ruby-red elixir works but they do have an educated guess.
Like lettuce and spinach, beetroot is rich in nitrate, which the body converts into nitrite. This, in turn, is a chemical trigger for another compound, nitric oxide.
Nitric oxide can dilate blood vessels and thus provide more oxygen to muscles. “But we think the key is that it seems to do a lot of weird and wonderful things within the muscle cells’ mitochondria, where oxidated energy is produced,” Jones said.
Earlier laboratory studies confirm the link between nitric oxide and increased energy output but further experiments are needed to see whether this truly is the magic ingredient.
The research was carried out by the University of Exeter and Peninsula Medical School and published in the Journal of Applied Physiology. The research team now hopes to conduct further studies to try to understand in more detail the effects of nitrate-rich foods on exercise physiology.
Corresponding author of the study, Professor Andy Jones of the University of Exeter’s School of Sport and Health Sciences, said: “Our study is the first to show that nitrate-rich food can increase exercise endurance. We were amazed by the effects of beetroot juice on oxygen uptake because these effects cannot be achieved by any other known means, including training. I am sure professional and amateur athletes will be interested in the results of this research. I am also keen to explore the relevance of the findings to those people who suffer from poor fitness and may be able to use dietary supplements to help them go about their daily lives.”
This study follows research by Barts and the London School of Medicine and the Peninsula Medical School (published in February 2008 in the American Heart Association journal Hypertension), which found that beetroot juice reduces blood pressure.
J Appl Physiol (August 6, 2009). doi:10.1152/japplphysiol.00722.2009
Submitted on July 6, 2009
Revised on July 27, 2009
Accepted on August 3, 2009
Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans
Stephen J. Bailey1, Paul Winyard1, Anni Vanhatalo2, Jamie R. Blackwell1, Fred J. DiMenna1, Daryl P. Wilkerson2, Joanna Tarr1, Nigel Benjamin3, and Andrew M. Jones1*
1 Exeter University
2 University of Exeter
3 University of Aberdeen Medical School
* To whom correspondence should be addressed. E-mail: email@example.com.
Pharmacological sodium nitrate supplementation has been reported to reduce the O2 cost of sub-maximal exercise in humans. In this study, we hypothesised that dietary supplementation with inorganic nitrate in the form of beetroot juice (BR) would reduce the O2 cost of sub-maximal exercise and enhance the tolerance to high-intensity exercise. In a double-blind, placebo-controlled, crossover study, eight males (aged 19-38 yr) consumed 500 mL per day of either beetroot juice (BR, containing 11.2 Â± 0.6 mM of nitrate) or blackcurrant cordial (as a placebo, PL, with negligible nitrate content) for six consecutive days, and completed a series of ‘step’ moderate-intensity and severe-intensity exercise tests on the last 3 days. On days 4-6, plasma [nitrite] was significantly greater following dietary nitrate supplementation compared to placebo (BR: 273 Â± 44 vs. PL: 140 Â± 50 nM; P<0.05) and systolic blood pressure was significantly reduced (BR: 124 Â± 2 vs. PL: 132 Â± 5 mmHg; P<0.01).
During moderate exercise, nitrate supplementation reduced muscle fractional O2 extraction (as estimated using near infra-red spectroscopy). The gain of the increase in pulmonary VO2 following the onset of moderate exercise was reduced by 19% in the BR condition (BR: 8.6 Â± 0.7 vs. PL: 10.8 Â± 1.6 mL.min-1.W-1; P<0.05). During severe exercise, the VO2 slow component was reduced (BR: 0.57 Â± 0.20 vs. PL: 0.74 Â± 0.24 L.min-1; P<0.05) and the time-to-exhaustion was extended (BR: 675 Â± 203 vs. PL: 583 Â± 145 s; P<0.05). The reduced O2 cost of exercise following increased dietary nitrate intake has important implications for our understanding of the factors which regulate mitochondrial respiration and muscle contractile energetics in humans.