Dietary flavonols reduce platelet aggregation, increase GFR and vasodilation

By Karla Gale

BOSTON (Reuters Health) – Examination of an isolated population for protective genes that might explain their freedom from age-related hypertension, led instead to the discovery that chronic consumption of flavonol-rich cocoa increases glomerular filtration rate (GFR) and vasodilation.

This and other findings related to the beneficial effects of flavonoids were reported at the 168th Annual Meeting of the American Association for the Advancement of Science (AAAS), held in Boston last weekend.

Dr. Norman K. Hollenberg, of Harvard Medical School in Boston, reported that Kuna Amerinds, an indigenous group residing in isolated islands off the coast of Central America, have a high salt intake but do not experience increasingly high BP with age. However, when Kuna natives migrate to urban areas, they develop hypertension that is unrelated to obesity.

It turns out that indigenous Kuna consume an average of 5 cups of relatively unprocessed cocoa per day. The renal plasma flow and GFR, as well as urinary nitrate-to-nitrite ratio, are higher in indigenous Kuna than in their counterparts who move to urban areas, a pattern consistent with nitric oxide synthase action.

Dr. Hollenberg's team tested cocoa levels in residents of Boston and found that renal plasma flow and GFR increased following consumption of the flavonol-rich cocoa.

Further supporting the vascular effect of a nitric oxide mechanism were the findings reported by Dr. Carl L. Keen of the University of California at Davis. His team's research, presented for the first time here at the AAAS, compared the effects of low-dose aspirin and a flavonol-rich cocoa drink. The reduced platelet aggregation was similar in both test arms.

"We saw lower concentrations of lipid peroxides and malonaldehyde after subjects drank the cocoa," Dr. Keen told Reuters Health. "These findings suggest that flavonol increases the body's oxidative defense, and does so with a mechanism different from that of aspirin."

The UC-Davis investigators observed flavonol blood levels between 0.5 and 1.0 micromolar, a concentration shown previously to affect platelet activation. In contrast to aspirin, where an irreversible enzymatic inhibition leads to a protective effect lasting for a day, the effect of the cocoa beverage peaked at about 4 hours and was no longer detectable by 6 to 8 hours after consumption.

This shortened effectiveness may be why it is important to consume three to five servings of fruits and vegetables throughout the day to see a long-term cardioprotective effect. The hope, Dr. Keen added, is that flavonoids or their analogs will provide new ways to protect cardiovascular health without the negative interactions associated with aspirin or other medications.

Dr. Harold H. Schmitz, of Mars, Inc., in Hackettstown, New Jersey, reports that his organization is working in cooperation with the United States Department of Agriculture to develop a comprehensive flavonoid food composition database.

"What we've been finding is that while flavonols are ubiquitous in plants, clearly some have a lot more than others," Dr. Schmitz told Reuters Health. "We're also learning that the way different plant foods are processed can have a profound influence on the level of active agents."

For example, he said, much of the chocolate consumed in Europe and the US contains low levels of flavonol because of the fermentation, roasting, and alkalinization that takes place during the manufacturing process. The reason the Kuna cocoa is heart-protective is because it is not subjected to these processing practices.

"Many drugs may be too targeted and powerful for some patients, so an approach taking advantage of a decreased intensity and magnitude of cardiovascular response is an appealing pharmaceutical route to pursue," Dr. Schmitz concluded

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