Scientists from Queen Mary University of London report that a 250 ml glass of beetroot juice reduced blood pressure in healthy volunteers to the same extent as a supplement containing 1,488 mg of nitrate. The findings have been published online in Hypertension.
"We showed that beetroot and nitrate capsules are equally effective in lowering blood pressure indicating that it is the nitrate content of beetroot juice that underlies its potential to reduce blood pressure,” said lead researcher, Professor Amrita Ahluwalia.
“We also found that only a small amount of juice is needed – just 250ml – to have this effect, and that the higher the blood pressure at the start of the study the greater the decrease caused by the nitrate.
"Our previous study two years ago found that drinking beetroot juice lowered blood pressure; now we know how it works,” added Prof Ahluwalia.
The researchers performed three separate studies: For the first one 21 people were randomly assigned to one of three groups: One group received potassium nitrate capsules (1488 mg of nitrate; Martindale Pharmaceuticals); an equivalent dose of potassium chloride (Martindale Pharmaceuticals) or 500 mL of low nitrate-containing water. In the second study, six additional people received either 248 or 744 mg of nitrate as potassium nitrate. The third study randomly assigned nine healthy subjects to drink 250 mL of beetroot juice (James White Drinks Ltd) or 250 mL of water.
In all of the groups, the researchers took blood samples and measured blood pressure at the start and then at regular intervals for 24 hours.
Results from the first and second study showed that the nitrate capsules raised blood nitrate levels, and that this increase was dependent on the dose given. The nitrate was found to reduce blood pressure levels, with the 1,488 mg dose reducing systolic blood pressure by a maximum of about 7 mmHg after 3 hours. No changes on blood pressure were observed in the potassium chloride group.
The third study showed that nitrate-rich beetroot juice raised blood nitrate levels, and this was accompanied by a maximum reduction of systolic blood pressure of about 5.4 mmHg.
Both the nitrate capsules and the beetroot were well tolerated, said the researchers.
Sick and healthy populations
The researchers note that the results are specific to healthy individuals, but they do propose that the data could also be extrapolated to people suffering from cardiovascular disease (CVD).
“Extrapolation of the beneficial effects of dietary (inorganic) nitrate to the wider population, including patients with different CVD, will require large-scale outcome trials to prove the thesis that dietary (inorganic) nitrate is a potential preventative measure or treatment for CVD,” wrote Ahluwalia and her co-workers.
“Furthermore, we suggest that important sex differences in baseline levels and handling of NOx species may underpin differences in blood pressure and CVD in the general population.
“Finally, there may be a role for nitrate in delaying and preventing hypertension, and supplementation either in water or by diet may provide a cheap and effective global health strategy to combat the prevalence of CVD,” they concluded.
Blood flow and sport
Beyond the potential cardiovascular benefits, beetroot juice may also be finding a foothold in the sport nutrition arena. A much publicized study by scientists at the University of Exeter in the UK reporting that beetroot juice may boost stamina and allow people to exercise for up to 16 per cent longer.
The vegetable juice’s nitrate content may reduce oxygen uptake to an extent that cannot be achieved by any other known means, making exercise less tiring, according to findings published in the Journal of Applied Physiology (doi:10.1152/japplphysiol.00722.2009).
“Our study is the first to show that nitrate-rich food can increase exercise endurance,” said Exeter’s Professor Andy Jones. “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.”
Published online ahead of print, doi: 10.1161/HYPERTENSIONAHA.110.153536
“Inorganic Nitrate Supplementation Lowers Blood Pressure in Humans. Role for Nitrite-Derived NO”
Authors: V. Kapil, A.B. Milsom, M. Okorie, S. Maleki-Toyserkani, F. Akram, F. Rehman, et al.