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Health benefits associated with flavonoids have been reported for decades, but it's still difficult for experts to make specific recommendations about which flavonoids to eat for specific health effects because of a lack of data. Antioxidants slow or prevent the oxidative process caused by substances called free radicals, which can cause cell dysfunction and the onset of heart disease and other health problems.
In the new study, Dr. Lee Hooper, a lecturer at the University of East Anglia in Norwich, U.K., and colleagues sifted through the 133 studies to look at the links between different flavonoid subclasses and flavonoid-rich foods on different risk factors for cardiovascular disease, such as unhealthy cholesterol, high blood pressure and blood flow.
Among the findings:
- Eating chocolate or cocoa increased a measure called flow-mediated dilation, which is a good indication of blood flow in the veins. It also reduced blood pressure, both systolic (the upper number, reflecting the maximum pressure exerted when the heart contracts) by about 6 points, and diastolic (the bottom number, reflecting the maximum pressure when the heart is at rest), by about 3.3 points. But it didn't seem to have an effect on so-called "bad" LDL cholesterol.
- Soy protein reduced diastolic blood pressure by almost 2 points of mercury and improved bad cholesterol but didn't improve so-called good HDL cholesterol. But those effects were found just for isolated soy protein, not for other soy products.
- A habit of green tea drinking reduced bad cholesterol levels, but drinking black tea boosted both systolic and diastolic pressure — by 5.6 points for systolic and 2.5 for diastolic.
As more research on flavonoids becomes available, it is likely that no single one will emerge as a "miracle food, but that many will contribute to our cardiovascular health," said Hooper, whose review was published in the July issue of The American Journal of Clinical Nutrition.
The new review helps define the role of foods rich in antioxidants, said Dr. Johanna Geleijnse, a nutritional epidemiologist at Wageningen University, the Netherlands, who co-authored an editorial to accompany the report.
"Evidence is accumulating that these substances are more important to cardiovascular health than vitamin C and vitamin E," and this most recent analysis strongly suggests good effects on blood pressure and blood vessel function, she said.
But much remains to be found out, she added.
Meanwhile, what to do? Eat a good mixture of the flavonoid-rich foods you like best, said Hooper. "For me, this would include lots of fruit, small amounts of a good dark chocolate (at least 70 percent cocoa), plus the basics like onions and green tea and an occasional glass of red wine."
SOURCES: Johanna M. Geleijnse, Ph.D., nutritional epidemiologist, Wageningen University, the Netherlands; Lee Hooper, Ph.D., S.R.D., lecturer, research synthesis and nutrition, University of East Anglia, Norwich, U.K.; July 2008, The American Journal of Clinical Nutrition
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