The study saw 29 middle-aged adults with pre-hypertension consuming juice containing 300 mg per day grape seed extract (GSE) or a placebo twice daily for six weeks. Blood pressure (BP) was monitored and blood samples were collected during the intervention period and at four weeks afterwards.
GSE significantly reduced systolic BP by 5.6% after six weeks of intervention. Diastolic blood pressure was also reduced but this was not significantly different from placebo at six weeks. BP returned to baseline four weeks after discontinuing GSE consumption. Subjects with the highest initial BP saw the most significant benefit.
The authors concluded: “GSE was found to be safe and to improve BP in people with pre-hypertension, supporting the use of GSE as a functional ingredient in a low-energy beverage for BP control.”
Grape seed extract
Grapes have been used traditionally for their medicinal value for thousands of years. Grape seed extract contains proanthocyanidins which have been studied for their antioxidant potential in a number of health conditions.
The vasodilator compounds found in GSE have been shown in previous studies to lower BP in subjects with metabolic syndrome, but effects on systolic and diastolic BP and pre-hypertension have been conflicting or inconclusive.
GSE is sold as a dietary supplement in liquid extract or tablet form.
'Reducing risk of heart disease'
Commenting on the results, researcher Britt Burton-Freeman from the Centre for Nutrition Research at the Institute for Food Safety and Health at Illinois Institute of Technology told us: “A few more people in the study would have likely made this a significant result for diastolic blood pressure.”
According to data from Blood Pressure UK, around one in three adults have high BP and percentages start to increase more around middle age.
Professor Graham MacGregor, chairman of Blood Pressure UK, told us he was sceptical of smaller studies that claimed to lower BP saying the important factors in lowering BP were reducing salt intake, increasing fruits and vegetables, avoiding being overweight and exercising more.
“If individuals want to take grapeseed juice for breakfast I’ve nothing against it but I think they must realise the evidence is provisional and not proven,” he told us.
Asked what he thought about the significant results on systolic but not on diastolic BP compared to placebo, he said although he hadn’t read the study in detail he would find this “odd”.
He stressed the importance of how the BP had been measured. “This is another variable that very often is not very well controlled in these small studies.”
Meanwhile Burton-Freeman said: “Keeping blood pressure in or near the normal ranges during early and middle age years can pay off later in life reducing risk of heart disease, as suggested by longitudinal epidemiological research.
“Future plans include follow-up functional foods with GSE and application of GSE in other populations.”
Source: British Journal of Nutrition
Published online ahead of print doi: 10.1017/S0007114515004328.
“Effects of grape seed extract beverage on blood pressure and metabolic indices in individuals with pre-hypertension: a randomised, double-blinded, two-arm, parallel, placebo-controlled trial”
Authors: E. Park, I. Edirisinghe, Y.Y. Choy, A. Waterhouse and B. Burton-Freeman