Grapes may protect against salt-induced hypertension: study

By Stephen Daniells

- Last updated on GMT

Related tags Blood pressure Hypertension

A diet rich in phytochemicals from grapes may reduce the blood pressure increases associated with high salt intake, according to a new animal study.

Rats fed a high salt diet supplement with grape powder were found to have lower blood pressure, better heart function, reduced inflammation throughout their bodies, and fewer signs of heart muscle damage than the rats fed a high slat diet without the grapes, according to new research from the University of Michigan.

The study adds to the growing body of research reporting the heart healthy benefits of grape and grape products. The researchers, led by Steven Bolling, note that despite the promising results from this rat study, more research is needed to

Salt is of course a vital nutrient and is necessary for the body to function, but campaigners for salt reduction, like the Consensus Action on Salt and Health (CASH) consider the average daily salt consumption in the western world, between 10 and 12g, far too high.

Numerous scientists are convinced that high salt intake is responsible for increasing blood pressure (hypertension), a major risk factor for cardiovascular disease (CVD) - a condition that causes almost 50 per cent of deaths in Europe.

"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 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,”​ he added.

Study details

Male Dahl rats, specially bred to be susceptible to salt-induced hypertension, were divided into five groups and fed a low salt diet, a low salt diet supplemented with grape powder, a high salt diet, a high salt diet plus grape powder, or a high salt diet plus the blood-pressure medicine, hydrazine. The feeding lasted for 18 weeks.

The rats in the high-salt grape and high-salt hydrazine groups did develop high blood pressure over time. However, their systolic blood pressures were lower than the high-salt rats that did not receive grapes.

Interestingly, the rats that received hydrazine along with a salty diet also had lower blood pressure, but the researchers report that their hearts were not protected from damage as they were in the grape-fed group.

Distortions to the size, weight and function of the animals’ hearts were also measured, as these are characteristics of heart failure. The researchers found that the high-salt grape group had less of a change than the high-salt hydrazine group. Moreover, the grape-fed rats’ hearts pumped more blood per unit of time, indicative of improved function.

Finally, the rats consuming the high-salt grape diet had lower levels of markers of inflammation and oxidative damage than rats consuming 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.

Bolling and his co-workers cautioned that further research is necessary to establish if the results can be replicated in humans.

The study was partly funded by the California Table Grape Commission, which also supplied the grape powder.

Source: Journal of Gerontology: Biological Sciences​October 2008, Volume 63A, Number 10, Pages 1034-1042“Chronic Intake of a Phytochemical-Enriched Diet Reduces Cardiac Fibrosis and Diastolic Dysfunction Caused by Prolonged Salt-Sensitive Hypertension”​Authors: E. M. Seymour, A.A.M. Singer, M.R. Bennink, R.V. Parikh, A. Kirakosyan, P.B. Kaufman, S.F. Bolling

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