LONDON, UK — A small, proof-of-principle study has demonstrated that the blood-pressure lowering effects of dietary nitrates–already documented in normotensives–are also seen in subjects with established hypertension.
Dr Amrita Ahluwalia (Barts and the London School of Medicine and Dentistry, UK) and colleagues have a track record of studying the interaction between dietary sources of biologically inert nitrate (NO3) and oral microflora, which converts the NO3 into bioactive nitrite (NO2). Circulating NO2 is known to cause vasodilation and lower blood pressure. Ahluwalia et al have previously proposed a pathway for nitrate-nitrite conversion, showing that beet juice, after coming into contact with human saliva, increases levels of plasma nitrate and nitrite and leads to significant blood-pressure decreases in healthy volunteers.
In their latest study, published online April 15, 2013 in Hypertension, Ahluwalia and colleagues, including senior author Dr Suborno Ghosh (Queen Mary University of London, UK) turned again to beetroot, which, along with green leafy vegetables, has high concentrations of inorganic nitrate. In a mouse model of hypertension, investigators first established a threshold nitrite dose at which blood pressure decreased in the hypertensive mice, but not in normotensive control mice. At higher doses, however, both strains of mice saw blood-pressure decreases.
The authors then tested the beet-juice effects in 15 hypertensive, drug-naive patients, randomized to either 250 mL of inorganic nitrate-rich beetroot juice or an equal volume of water. The “dose” of juice elevates nitrite levels approximately 1.5 fold–a rise previously shown to have no significant BP-lowering effect in subjects with normal blood pressure.
In patients who drank the juice, systolic blood pressure dropped by a mean of 11.2 mm Hg between three and six hours after consumption (vs 0.7 mm Hg in subjects who drank water). By 24 hours, clinic systolic BP remained significantly lower in the beet-juice group and roughly 7.2 mm Hg lower than baseline. Peak drop in diastolic BP also occurred within the first six hours, dropping by a mean of 9.6 mm Hg. Pulse-wave velocity also decreased in the beet-juice group, but not in the controls.
“Our observations . . . support the concept of dietary nitrate supplementation as an effective, but simple and inexpensive, antihypertensive strategy,” the authors conclude.
To heartwire , Ahluwalia underscored the finding that nitrate in beets appears to be even more potent in hypertensives than in normotensives. “In this new study we used a dose that had little to no effect upon blood pressure in healthy volunteers; in contrast, this dose caused a substantial decrease in blood pressure (~12 mm Hg) in the patients, suggesting that dietary nitrate is more potent, and therefore potentially one needs less to produce an important blood-pressure–lowering effect.”
She added: “It is also true that while we all know that eating fruits and vegetables is good for the cardiovascular system, exactly why this is the case is not certain. Studies have shown that of all the different fruit and vegetables out there it is the green leafy vegetables that provide the greatest protection against heart attacks and strokes. What is true about these vegetables is that they represent the major source of nitrate in our diet.”
She also stressed the limitations of the study: while “impressive,” the BP-lowering effects of beet juice consumption were measured only over 24 hours and in very small numbers. “Whether this effect can be sustained in the long term is not yet known, and further clinical studies that assess the effects over longer periods of time and in larger cohorts are needed,” she said.