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 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 an 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.
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
study's 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
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
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.