New research from the US on laboratory rats suggests that eating grapes could help to fight high blood pressure resulting from a salty diet and could also reduce other cardiovascular risks and heart muscle damage. The effect is thought to be due to the high level of flavonoids in grapes.
The study was led by researchers from the University of Michigan Cardiovascular Center in Ann Arbor, and is published in the October issue of the Journal of Gerontology: Biological Sciences.
For the study, the researchers investigated the effect of dried grape powder made from regular table grapes (a mix of green, red and black varieties) when mixed in the diet of laboratory rats that had been bred to develop high blood pressure when fed on a salty diet (the Dahl Salt-Sensitive or Dahl- SS rat model).
The 60 rats were in five groups depending on how much salt was in their diet: high salt or low salt, whether they also had the grape powder, and whether they were given a mild dose of a common blood pressure drug (the vasodilator hydralazine).
Thus the five groups were: (1) low salt only, (2) low salt plus grape powder, (3) high salt only, (4) high salt plus grape powder, and (5) high salt plus vasodilator hydralazine.
The results showed that:
- After 18 weeks, compared to their counterparts on diets without grape powder, the rats that had the grape powder had lower blood pressure, better heart function, reduced inflammation in their bodies, and less heart muscle damage.
- The rats that had the blood pressure medication and high salt diet also had lower blood pressure, but their heart damage was greater than in the grape powder fed groups.
The study was part of Mitchell Seymour’s doctoral research in nutrition science at Michigan State University. Seymour, who manages the U-M Cardioprotection Research Laboratory under the supervision of U-M heart surgeon Dr Steven Bolling, said that the findings explained their theory that there was something special about grapes, beyond the simple blood-pressure reducing effect we already expect from diets rich in fruit and vegetables.
Bolling, who is also professor of cardiac surgery at the U-M Medical School said that the animals in the study were not unlike millions of Americans who develop heart failure because of many years of diet-related high blood pressure.
“The inevitable downhill sequence to hypertension and heart failure was changed by the addition of grape powder to a high-salt diet,” said Bolling.
Although grapes have many natural compounds that could be responsible for this effect, the researchers think in this case it is the flavonoids, either by affecting cells directly or via their antioxidant properties.
“These flavonoids are rich in all parts of the grape – skin, flesh and seed, all of which were in our powder,” said Bolling.
Other studies have already suggested that flavonoids may reduce other potentially harmful molecular and cellular body processes.
Bolling said they were not about to tell patients to stop taking their blood pressure medication and eat only grapes. However, people who want to lower their blood pressure should cut down on the amount of salt in their diet.
“There is, as we now know, a great variability, perhaps genetic even, in sensitivity to salt and causing hypertension,” said Bolling.
“Some people are very sensitive to salt intake, some are only moderately so, and there are perhaps some people who are salt resistant. But in general we say stay away from excess salt,” he added.
The study was partly sponsored by the California Table Grape Commission, but the authors pointed out that they had no influence on the design and execution of the research, or in the journal write up.
“Chronic Intake of a Phytochemical-Enriched Diet Reduces Cardiac Fibrosis and Diastolic Dysfunction Caused by Prolonged Salt-Sensitive Hypertension”.
E. M. Seymour, Andrew A. M. Singer, Maurice R. Bennink, Rushi V. Parikh, Ara Kirakosyan, Peter B. Kaufman, and Steven F. Bolling.
J. Gerontol. A Biol. Sci. Med. Sci. 2008 63: 1034-1042.
Sources: Journal abstract, University of Michigan Health System.
Written by: Catharine Paddock, PhD.