Monday December 20 2010
Nitrate-rich juice was compared to juice with the nitrate removed
“Drinking beetroot juice could help the elderly lead more active lives,” the Daily Mail reported. The newspaper called the juice “the elixir of life”, saying that it has been found to improve walking effort by 12%.
The news story is based on a small study in nine healthy young men, which tested their exercise response to beetroot juice over a six-day period. The aim was to see whether any benefit from the juice was due to its nitrate content, and so the men were also tested for a further six days on a beetroot juice with the nitrate removed. The nitrate-rich juice was associated with lower blood pressure and oxygen expenditure while walking and running, and delayed exhaustion.
However, with only nine men in the study, it is unlikely that these results are representative of the whole population. Also, if there is a benefit from beetroot juice, it is unclear whether the results from these laboratory tests would translate into a noticeable difference in normal, daily life. There is no evidence that beetroot juice is the “elixir of life”.
Where did the story come from?
This study was carried out by researchers from the University of Exeter. Sources of funding are not given. The research was published in the Journal of Applied Physiology.
This was a study of healthy men with an average age of 22, and it is unclear why the Daily Mail has applied the results to the elderly. It has also not addressed the study’s main limitations, which include its very small sample size.
What kind of research was this?
The aim of this research was to investigate the effect of beetroot juice on the body during submaximal exercise (less than the maximum of what a person is capable of). The researchers were interested in whether the high nitrate content of the juice could lower blood pressure and reduce oxygen intake.
The study design was a double blind, randomised crossover trial, examining the effects of supplementation with beetroot juice and nitrate-depleted beetroot juice on blood pressure, oxidative capacity of mitochondria within muscles (Qmax), which is a measure of how efficiently the muscles use oxygen, and the physiological response to walking, moderate-intensity running and severe-intensity running.
What did the research involve?
The researchers recruited nine healthy young men (average age 22) who were asked to report to the laboratory 10 times over a four-to-five-week period. At the start, the men were given treadmill tests and their maximal oxygen intake, blood pressure, heart rate, lung function and blood nitrite concentration were assessed.
They were then randomised to receive either 0.5L per day of beetroot juice (containing about 6.2mmol of nitrate) or nitrate-depleted juice (containing about 0.003mmol of nitrate) for six days. They took part in repeat treadmill exercise tests on days four and five. On day six, the men were asked to perform knee extension tests while scans were taken of their body with a superconducting magnetic resonance scanner. The knee extensions were designed to reduce muscle phosphocreatinine concentration (PCr) and allow them to estimate muscle mitochondrial oxidative capacity (Qmax).
Tests were then repeated during a second supplementation period when the men received the alternative drink for six days.
What were the basic results?
Compared with drinking the nitrate-depleted juice, six days of beetroot juice elevated the men’s plasma nitrite concentration (373nM versus 183 with the depleted solution; p<0.05) and reduced their systolic blood pressure (124mmHg versus 129mmHg; p<0.01).
Beetroot juice also reduced the men’s oxygen requirements during treadmill walking, compared with the depleted juice (0.70L per minute versus 0.87; p<0.01). This also applied to moderate-intensity running (2.10L per minute versus 2.26 with the depleted solution; p<0.01) and severe-intensity running (3.50L per minute versus 3.77 with the depleted solution; p<0.01). Beetroot juice also reduced the time to exhaustion during severe-intensity running by 15%, compared with the depleted juice.
There was no difference between drinks in the effect on muscle Qmax.
How did the researchers interpret the results?
The researchers say that their findings indicate that six days’ worth of beetroot juice supplementation has a positive effect on the physiological response to exercise, and this can be attributed to the high nitrate content of the juice.
This small crossover trial found that short-term supplementation with nitrate-rich beetroot juice reduced systolic blood pressure, as well as oxygen expenditure during walking and moderate-intensity and severe-intensity running. It also appeared to increase the time to exhaustion during both severe-intensity running and knee-extension exercises.
However, this study's findings are greatly limited by its small size, as it was in only nine men, and it is unlikely that these results are representative of the whole population. The experimental period was also very short, at only six days.
It is unclear why the Daily Mail has stated that the findings of this study are directly relevant to the elderly as the study involved healthy young men with an average age of 22.
There is no evidence from this study that beetroot juice is the “elixir of life”.
Amended: December 24, 2010