Reference
Muggeridge DJ, Howe CC, Spendiff O, Pedlar C, James PE, Easton C. A single dose of beetroot juice enhances cycling performance in simulated altitude. Med Sci Sports Exerc. 2014;46(1):143-150.
Design
Participants completed a series of 4 exercise trials on a cycle ergometer consisting of an initial graded test to exhaustion and then 3 performance trials. The performance trials consisted of 15 minutes of submaximal steady-state exercise at 60% maximum work rate and a 16.1 km time trial (TT). Three hours before the second and third trials, participants ingested either beetroot juice or a placebo. Oxygen pressure was adjusted to simulate being at an altitude of ~2,500 meters (8,200 feet).
Participants
Nine competitive amateur male cyclists (age 28 ± 8 y).
Study Medication and Dosage
Participants consumed either 70 mL beetroot juice (~2.4 ounces) or the same quantity of a nitrate-depleted beetroot juice as a placebo.
Outcome Measures
Plasma nitrate and nitrite levels were measured immediately before exercise. Oxygen consumption (VO2) during steady-state exercise and the time to ride 16.1 miles in a time trial were measured.
Key Findings
Drinking beetroot juice increased plasma nitrate and nitrate compared to placebo juice. VO2 during steady-state exercise was lower after drinking beetroot juice compared to after drinking placebo juice. The time trial performance was significantly faster after beetroot juice consumption (1,664 ± 14 s) than it was after placebo (1,702 ± 15 s, P=0.021).1
Practice Implications
Serious bike riders live for their sport. Beetroot juice is a legal means to improve their performance. This isn’t the only beet juice cycling study.
Cermak et al reported in February 2012 that after 6 days of drinking a beet concentrate, equivalent to 2 cups a day of whole juice, the 12 riders in the double-blind clinical trial improved their 10-km time trial performance by approximately 12 seconds.2
These new results from Muggeridge et al are consistent with earlier published data that suggest that beet juice has a significant impact on physiology. In 2008, AJ Webb and colleagues in London reported that drinking 2 cups of beet juice lowered blood pressure almost 10 points in healthy volunteers and that beet juice protected blood vessels from injury while lowering the risk of blood clot formation.3 Coles and Clifton reported in December 2012 that beet juice lowers blood pressure in “free-living adults,”4 the possible human equivalent to “free-range chickens.”
Beet juice increases muscle efficiency, allowing the muscles to do the same work with less oxygen, allowing people to walk, run, or perform exercises with a lower “cost” in oxygen.5,6 Consuming beet juice creates a tolerance for higher-intensity exercise.7 Blood pressure stays lower during intense exercise, putting less strain on the heart.8
Not all trials have demonstrated these benefits. In a study published in February 2013, elite athletes who drank half a liter of beet juice (500 mL) daily for 6 days did not perform significantly differently than those who drank a nitrate-depleted placebo drink.9 Perhaps the effect is less pronounced in more fit athletes?
In an April 2013 paper, Muggeridge et al reported that the same 70-mL dose of beet juice given in their current study did not improve time trial performance in flat-water kayakers.10 In that trial, they did not simulate high-altitude conditions. It may be that the benefit of beet juice is more pronounced at lower oxygen pressures.
Though not always useful, many athletes have added beet juice to their list of “legal” tricks to enhance athletic performance. We may use this same trick for better ends—in particular, aiding those patients with compromised circulation or impeded oxygen levels.
We should also consider using beet juice for neurodegenerative diseases. In a January 2011 study, researchers from Wake Forest University reported on changes in cerebral circulation in volunteers who had drunk beet juice. These study participants were older than the cyclists, with an average age of 75 years. Nuclear magnetic resonance imaging (MRI) was used to measure bloodflow to various parts of the brain after participants consumed beet juice. Although the total amount of blood that reached the brains remained constant, more blood flowed to the frontal lobe white matter, especially between the dorsolateral prefrontal cortex and anterior cingulate cortex. These areas of the brain are involved in executive functioning.11
Beet juice may just be the most concentrated edible form of nitrate in nature. Beets may contain as much as 2,500 mg of nitrate per kilogram. Broccoli, carrots, cauliflower, cucumber, pumpkin, and even V-8 vegetable juice contain less than 1/10 this amount.12 Average dietary intake of nitrates for adults in the US is ~60–120 mg/d. About 80% comes from vegetables, so vegetarians may consume above-average amounts. People who follow the DASH diet for treating hypertension may consume 5.5 times the average nitrate amount.
Once eaten, nitrates are converted to nitrites that are in turn converted to nitric oxide. Nitric oxide is a potent vasodilator. This higher nitric oxide production may explain the benefits.
The benefits of a high-nitrate diet may outweigh the danger, if any, that they bring.
Jon Lundberg at the Karolinski Institute, in a 2006 article in the journal Nitric Oxide, was perhaps the first to propose the theory that green leafy vegetables protect against cardiovascular disease because they contain nitrates.13 Kapil et al proved that the nitrates in beets were responsible for their cardiovascular effects in 2010 by comparing beet juice with potassium nitrate capsules.14
Many readers will recall that in years past, both nitrates and nitrites were thought to be unsafe, and patients have long been exhorted to avoid excess consumption of them. It is these same nitrates whose presence in smoked meats and bacon worried us. The benefits of a high-nitrate diet may outweigh the danger, if any, that they bring.15
Martijn Katan, writing in the July 2009 American Journal of Clinical Nutrition, suggests that the evidence of harm from nitrates that prompted the concerns back in the early 1960s and that led to the setting of low consumption limits have yet to be confirmed. Admittedly, the benefits of consuming a high-nitrate diet have also not been confirmed, at least in large randomized controlled prospective trials.16
If nitrates are now good for our patients to eat, we may need to reassess our appraisal of the methods by which vegetables are grown. Because of the higher use of fertilizer, hothouse-grown lettuce can contain 8 times more nitrate than lettuce grown in a farmer’s field.17 As a result, organic versions of vegetables may contain far less nitrate than their “regular” counterparts because they are not treated with high-nitrogen fertilizers. This information would argue against our encouraging patients with high blood pressure to consume organic produce. It would instead suggest we encourage these patients to eat non-organic hothouse grown vegetables. Now that’s some odd food for thought.
Several recent in vitro trials on beets and the chemotherapy drug doxorubicin should be mentioned.
Beet juice and the nitrate contained therein may eventually prove to be useful for patients treated with the chemotherapy drug doxorubicin. Beets may both reduce doxorubicin cardiotoxicity and increase its effectiveness at killing cancer cells.
A 2011 article by Kapadia et al comparing the cancer inhibitory effect of beet juice versus doxorubicin reported that while beet juice was less effective than the drug, it still significantly inhibited growth of prostate, breast, skin, and liver cancer cells.18
In May 2012, Xi et al reported that nitrate protects against doxorubicin-caused cardiotoxicity and proposed a “novel concept of using dietary supplementation of inorganic nitrate to reduce [doxorubicin-] … induced cardiac cellular damage and dysfunction.” They estimated that nitrates supplied at just 4 times the World Health Organization’s Acceptable Daily Intake “alleviated [doxorubicin]-induced left ventricular dysfunction and mitochondrial respiratory chain damage.”19 Beets are such an excellent food source for inorganic nitrate that in research papers the terms beet juice and inorganic nitrate are used interchangeably.20 Recall that simply following the DASH Diet for hypertension supplies this amount of nitrate.
In June 2013, Kapadia et al reported that a combination of the doxorubicin and beet-supplied nitrate had a synergistic effect, inhibiting the growth of pancreatic, breast, and prostate cancer cell lines, suggesting the “potential of red beetroot extract-doxorubicin combination.”21
Clinical trials give us a solid basis for encouraging patients to consume beet juice for cardiovascular disease and in other situations in which increased nitric oxide may be advantageous. Whether using beet juice in conjunction with doxorubicin is advantageous has yet to be proven. These days, when patients tell me that they are making fresh vegetable juice each day, I can’t help but ask, “Are you adding beets?”
