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Benefit of grapes may be more than skin deep,
U-M animal study finds
ANN ARBOR, Mich. — Can a
grape-enriched diet prevent the downhill
sequence of heart failure after years of high
blood pressure?
A
University of Michigan Cardiovascular Center
study suggests grapes may prevent heart health
risks beyond the simple blood pressure-lowering
impact that can come from a diet rich in fruits
and vegetables. The benefits may be the result
of the phytochemicals – naturally occurring
antioxidants – turning on a protective process
in the genes that reduces damage to the heart
muscle.
The study, performed in
laboratory rats, was presented recently at the
2009 Experimental Biology convention in New
Orleans.
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. Comparisons
were made between rats consuming the grape
powder and rats 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.
After 18 weeks, the rats
that received the grape-enriched diet powder had
lower blood pressure, better heart function, and
fewer signs of heart muscle damage than the rats
that ate the same salty diet but didn’t receive
grapes.
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.
“There are the small
changes that diet can bring, but the effect of
grape intake on genes can have a greater impact
on disease down the road,” said E. Mitchell
Seymour, M.S., who led the research as part of
his doctoral work in nutrition science at
Michigan State University. He manages the
U-M Cardioprotection Research Laboratory,
which is headed by U-M cardiac surgeon Steven
Bolling, M.D.
Heart cells, like other
cells in the body, make a antioxidant protein
called glutathione, which is one of our first
defenders against damaging oxidative
stress. High blood pressure causes oxidative
stress in the heart and lowers the amount of
protective glutathione. However, intake of
grapes actually turned on glutathione-regulating
genes in the heart and significantly elevated
glutathione levels.
This may explain why the
hearts of grape-fed animals functioned better
and had less damage.
Bolling said the latest
results take research on the health benefits of
grapes “a step further” by examining the
mechanisms impacted by antioxidant-rich grapes.
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. The animals are
similar to
Americans who have elevated
blood pressure related to diet, and who develop
heart failure over time because of prolonged
hypertension.
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.
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.
In all, the researchers
say, the study further demonstrates that a
grape-enriched diet can have broad effects on
the development of hypertension and the risk
factors that go with it. Whether the effect can
be replicated in humans, they say, remains to be
seen.
University of Michigan
Cardiovascular Center
http://www.med.umich.edu/cvc/
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