Grapes May Be Ultimate Weapon to Fight High Blood
Pressure, Salty Diet and Protect Heart
Research shows grape intake reduces hypertension,
signs of heart muscle damage, and improves heart function in lab rats
'Something within the grapes themselves has a direct impact on
cardiovascular risk'
Oct. 29, 2008 - Could eating grapes help fight high
blood pressure related to a salty diet? And could grapes calm other
factors that are also related to heart diseases such as heart failure? A
new University of Michigan Cardiovascular Center study gives tantalizing
clues to the potential of grapes to reduce cardiovascular risk.
The effect is thought to be due to the high level
of phytochemicals naturally occurring antioxidants that grapes
contain..
The new study is published in the October issue of
the Journal of Gerontology: Biological Sciences,
The study was performed in laboratory rats. The
researchers noted that while these study results are extremely
encouraging, more research needs to be done.
The researchers studied the effect of regular table
grapes (a blend of green, red, and black grapes) that were mixed into
the rat diet in a powdered form, as part of either a high- or low-salt
diet.
They performed many comparisons between the rats
consuming the test diet and the control rats receiving no grape powder
including some that received a mild dose of a common blood-pressure
drug. All the rats were from a research breed that develops high blood
pressure when fed a salty diet.
In all, after 18 weeks, the rats that received the
grape-enriched diet powder had lower blood pressure, better heart
function, reduced inflammation throughout their bodies, and fewer signs
of heart muscle damage than the rats that ate the same salty diet but
didnt receive grapes.
The rats that received the blood-pressure medicine,
hydrazine, along with a salty diet also had lower blood pressure, but
their hearts were not protected from damage as they were in the
grape-fed group.
Says Mitchell Seymour, M.S., who led the research
as part of his doctoral work in nutrition science at Michigan State
University, These findings support our theory that something within the
grapes themselves has a direct impact on cardiovascular risk, beyond the
simple blood pressure-lowering impact that we already know can come from
a diet rich in fruits and vegetables.
Seymour manages the U-M Cardioprotection Research
Laboratory, which is headed by U-M heart surgeon
Steven Bolling, M.D.
Bolling, who is a professor of cardiac surgery at
the
U-M Medical School, notes that the animals in the study were in a
similar situation to millions of Americans, who have high blood pressure
related to diet, and who develop heart failure over time because of
prolonged hypertension.
The inevitable downhill sequence to hypertension
and heart failure was changed by the addition of grape powder to a
high-salt diet, he says.
Although there are many natural compounds in the
grape powder itself that may have an effect, the things that we think
are having an effect against the hypertension may be the flavanoids
either by direct antioxidant effects, by indirect effects on cell
function, or both. These flavanoids are rich in all parts of the grape -
skin, flesh and seed, all of which were in our powder. Bolling
explains.
Such naturally occurring chemicals have already
been shown in other research, including previous U-M studies, to reduce
other potentially harmful molecular and cellular activity in the body.
Although the current study was supported in part by
the California Table Grape Commission, which also supplied the grape
powder, the authors note that the commission played no role in the
studys design, conduct, analysis or the preparation of the journal
article for publication.
Seymour also receives funding from the
National Heart, Lung and Blood Institute, part of the National
Institutes of Health, through a National Research Service Award.
Though its true that your mom told you to eat all
your fruits and your vegetables, and that we are learning a lot about
what fruits, including grapes, can do in this particular model of
hypertension and heart failure, we would not directly tell patients to
throw all their pills away and just eat grapes, says Bolling.
However, research on grapes and other fruits
containing high levels of antioxidant phytochemicals continues to show
promise. So does research on the impact of red wine on heart health,
though that issue is also far from settled.
The U-M team notes that a clinical research on
grapes may be a possibility in the future, but is not currently planned.
In the meantime, Bolling says, people who want to
lower their blood pressure, reduce the risk of heart failure, or help
their weakened hearts retain as much pumping power as possible should
follow tried-and-true advice: Cut down on the amount of salt you get
through your food and drink.
There is, as we now know, a great variability,
perhaps genetic even, in sensitivity to salt and causing hypertension,
he says. 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 notes that the popular DASH diet, which is low
in salt and high in fruits and vegetables, has been proven to reduce
mild high blood pressure without medication. The dose of whole table
grape powder that was consumed in the study was roughly equivalent to a
person eating nine human-sized servings of grapes a day. Currently, five
to nine servings of fruits and vegetables are recommended as part of the
DASH diet.
The rats in the study were from a strain called
Dahl rats, which have been specially bred to all be susceptible to
salt-induced hypertension. This allowed the researchers to look at a
uniform sample of rats that would be affected in the same way by their
diet, so that the effects of the salt level, grape powder and hydrazine
could be seen clearly.
Each group of 12 rats was fed the same weight of
food each day, with powdered grapes making up 3 percent of the diet (by
weight) for rats that received grapes as part of either a low-salt or
high-salt diet. The rats that received hydrazine were fed it through
their water supply in a dose that has been previously shown to be
effective in reducing blood pressure.
The rats in the high-salt grape and high-salt
hydrazine groups did develop high blood pressure over time, but they had
lower systolic blood pressures than the high-salt rats that did not
receive grapes.
The researchers also measured the distortion of the
heart size, weight and function that occurred over time
characteristics of heart failure and found that the high-salt grape
group had less of a change than the high-salt hydrazine group.
Parameters related to the diastolic blood pressure an important factor
in human heart failure and to the hearts relaxation during the
diastolic phase also changed in just the high-salt grape group. Finally,
the grape-fed rats had improved cardiac output, or more blood pumped per
unit of time.
The researchers also looked for signs of
inflammation, oxidative damage and other molecular indicators of cardiac
stress. Again, the rats that received the high-salt grape diet had lower
levels of these markers than rats that received the high-salt diet with
hydrazine and even the low-salt grape-eating rats had lower levels
than the rats that received a low-salt diet alone.
In all, the researchers say, the study demonstrates
that a grape-enriched diet can have broad effects on the development of
hypertension and the risk factors that go along with it. Whether the
effect can be replicated in humans, they say, remains to be seen.
For more information on the DASH diet, which has
already been shown to lower blood pressure in people, visit
http://www.nhlbi.nih.gov/health.
Oct.
7, 2008