The benefits were linked to the nitrate content of the vegetable, and suggest an alternative explanation for the heart-healthy potential of vegetable-rich diets previously attributed to their antioxidant vitamin content.
"Our research suggests that drinking beetroot juice, or consuming other nitrate-rich vegetables, might be a simple way to maintain a healthy cardiovascular system, and might also be an additional approach that one could take in the modern day battle against rising blood pressure," said Professor Amrita Ahluwalia of the William Harvey Research Institute at Barts and The London School of Medicine.
The researchers recruited 14 health volunteers and randomly assigned them to drink 500 ml of beetroot juice (Planet Organic) or water during a 30 minutes period.
Blood pressure (BP) was measured every 15 minute for one hour before and three hours after consuming the beverage, then every hour for six hours, with a final reading after 24 hours.
Writing in Hypertension - Journal of the American Heart Association , the researchers report that BP was "substantially reduced" three hours after consuming the beetroot juice.
Moreover, a degree of reduction continued to be observed until up to 24 hours after ingestion.
The decrease in BP correlated with peak increases in plasma nitrite concentration, they said, with the conversion of nitrate to nitrite occurring in the saliva by bacteria on the tongue.
This nitrite-rich saliva was subsequently swallowed, and underwent further conversion in the acidic conditions of the stomach into nitric oxide or re-entered the circulation as nitrite.
"[The] reduction in BP correlated with the appearance and peak levels of nitrite in the circulation; an effect that was absent in individuals within whom the enterosalivary circuit was disrupted by avoidance of swallowing," wrote lead author Andrew Webb.
"These observations, together with the fact that plasma nitrite, and not nitrate, concentration correlated with the decreases in BP implicates nitrite as the likely functional mediator of the beetroot juice-induced effects on BP."
Commenting on the mechanism, the researchers stated that it was unknown how nitrite mediates blood pressure reductions, but noted that recent research has reported that nitrite can act as a potent vasodilator, which opens up blood vessels and improves circulation.
In an accompanying editorial in the same journal, David Wink and Nazareno Paolocci from National Institutes of Health and The Johns Hopkins Medical Institutions, respectively, said the study may provide important insights into a number of questions and problems associated with public health.
"For example, the use of dietary nitrite may be helpful during the administration of nonsteroidal antiinflammatory drugs (NSAIDs) which is still a serious problem," wrote Wink and Paolocci.
"These antiinflammatory drugs have been found to have beneficial effects in numerous chronic diseases, from cancer to arthritis.
However, their chronic use increases cardiovascular risks and stomach ulceration, which has dampened the enthusiasm for long-term treatment with these drugs.
"Nitrite here provides again a potential pharmacological shelter in that nitrate levels in drinking water appears to strengthen the integrity of the gastric mucosa during diclofenac administration by generating NO in the stomach." Talking to NutraIngredients.com , Professor Ahluwalia said: "For us the most pressing issues now are whether the dietary nitrate is as effective, if not more, in individuals with hypertension and we hope, pending funding, to be in a position this year to pursue this issue.
"We would also like to determine whether one can consume lower amounts of nitrate than in our study and still see the beneficial effects of the juice and we are currently looking at much lower volumes of juice in this respect.
"However, it is likely that the juice will be more effective in hypertensives since it is an established fact that vasodilating drugs give bigger blood pressure responses in hypertensives than in normotensives," added Professor Ahluwalia.
High blood pressure (hypertension),defined as having a systolic and diastolic blood pressure (BP) greater than 140 and 90 mmHg, is a major risk factor for cardiovascular disease (CVD) - a disease that causes almost 50 per cent of deaths in Europe, and reported to cost the EU economy an estimated €169bn ($202bn) per year.
Source: Hypertension - Journal of the American Heart Association Published online ahead of print 4 February 2008, doi: 10.1161/HYPERTENSIONAHA.107.103523 "Acute blood pressure lowering, vasoprotective and anti-platelet properties of dietary nitrate via bioconversion to nitrite" Authors: Andrew J. Webb, N. Patel, S. Loukogeorgakis, M. Okorie, Z. Aboud, S. Misra, R. Rashid, P. Miall, J. Deanfield, N. Benjamin, R. MacAllister, A.J. Hobbs, and A. Ahluwalia Editorial: Hypertension - Journal of the American Heart Association Published online 4 February 2008, doi: 10.1161/HYPERTENSIONAHA.107.106617 "Mother Was Right: Eat Your Vegetables and Do Not Spit!
When Oral Nitrate Helps With High Blood Pressure" Authors: D.A. Wink and N. Paolocci