Flavonoids are polyphenolic molecules that are produced by plants. In plants, flavonoids are thought to be used as attraction molecules for insects as well as antioxidants to protect fruits and other delicate and important structures from environmentally produced free radicals. In humans the antioxidant effects of flavonoids are well reported. Of the flavonoids, the flavan-3-ol group is perhaps one of the most well studied. Found in tea and chocolate, flavan-3-ols, often called catechins, have been shown to have numerous health benefits in humans possibly because of their radical scavenging effects. Isoflavones are not true flavonoids, but are often grouped together by researchers because of their structural similarities. Isoflavones differ from other flavonoids in that they are known to possess oestrogenic activity in addition to their free radical scavenging ability. Combinations of flavonoids such as catechins and isoflavones are increasingly being investigated for their synergistic effects on cardiovascular disease.
In a recent study published in the American Journal of Clinical Nutrition1, researchers administered a 27 gram dose of chocolate containing 850 mg of catechins and 100 mg of isoflavones or a placebo to postmenopausal women with type 2 diabetes for 1 year. The chocolate was standardised to contain 90 mg of epicatechin, as this catechin has been shown to be responsible in part for some of the beneficial effects of tea and chocolate. Those subjects receiving the flavonoid enriched chocolate showed a reduced variability in their pulse pressure variability, suggesting that the flavonoids were modulating the homeostatic mechanisms controlling blood pressure. The authors calculated that this effects would have produced a 10 % reduction in cardiovascular disease risk. Reductions in mean blood pressure also occurred but these did not reach statistical significance. All subjects were taking statins, and so it is unclear what effects the chocolate would have had on healthy non-statin taking subjects.
These results support the a growing body of evidence that suggest that flavonoids can favourably modulate blood pressure over the long-term. This may occur because flavonoids are able to act as antioxidants and in this role can protect the endothelial lining of arteries. Endothelial dysfunction can occur when oxidative stress modifies the endothelium by inhibiting the formation of nitric oxide, a messenger molecule required for correct vascular function, particularly the elastic effects of arteries in response to flow induced pressure changes. Interestingly, it has been noted that some subjects are able to convert the isoflavone daidzein to a metabolite called equol through the action of gut bacteria. Those subject able to undertake this conversion had larger reductions in diastolic blood pressure, mean arterial blood pressure and pulse wave velocity (a measure of arterial elasticity) compared to those subjects that could not produce equol. The strains of bacteria in the gut may therefore play an important role at modulating the beneficial effects of isoflavones.
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