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Division of Preventive Medicine
Department of Medicine
Brigham and Women’s Hospital and Harvard Medical School
Boston, MA 02215
E-mail: hsesso{at}hsph.harvard.edu
Dear Sir:
We appreciate Donovan’s comments regarding our recent article on dietary flavonoids and the risk of cardiovascular disease (CVD) in women (1). We agree that the terminology used not only in our article but in all articles on flavonoids in their various forms suffers from varying degrees of inconsistency. This is not surprising because thousands of different flavonoids are found in foods and beverages, and, at least until recently, there was no single nutrient database that included all of the subclasses of flavonoids in sufficient detail. In our article, we explicitly stated that "total flavonoids represent the sum of the individual selected flavonols and flavones." Still, in the interests of avoiding any possible misinterpretation of our conclusions, we wish to clarify our statements on flavonoid food sources and "total" flavonoid intake.
First, a more specific conclusion from our data would be that the observed relations between various flavonoid food sources and CVD were not mediated by the flavonols and flavones that composed our limited flavonoid database. Whether our findings extend to other major flavonoid subclasses is a critical research question that needs to be answered in future studies on flavonoid food sources and CVD.
The recent release of an expanded flavonoid database by the Nutrient Data Laboratory of the US Department of Agriculture, Agricultural Research Service has created potentially important opportunities for research on flavonoids and health (2). In 2002 the US Department of Agriculture, Agricultural Research Service also released data on the isoflavone content of foods, including the amounts of daidzein, genistein, glycitein, and total isoflavones (3), but these data have yet to be fully integrated into analyses examining soy-based food products and chronic disease. Questions surrounding the specific roles of these various flavonoid subclasses in the associations of tea, yellow onions, apples, chocolate, red wine, soy products, and other common flavonoid food sources with the risk of CVD and other chronic diseases await clarification. The study by Arts et al (4) on dietary catechins and ischemic heart disease mortality is an important first step; however, the reported strong correlation between catechins and tea intake (r = 0.98) illustrates how researchers must be careful to distinguish food-specific effects from flavonoid-specific effects when interpreting the results of any study.
The notion of total flavonoid intake is therefore a work in progress as the new databases begin to be incorporated into data analyses. With thousands of different flavonoids found in fruit, vegetables, and beverages, all studies on flavonoids inherently underestimate true total flavonoid intake. This parallels the challenges involved in quantifying dietary carotenoids, of which > 600 have been identified (5).
The hypothesis that dietary flavonoids reduce the risk of CVD offers tremendous potential based upon the total evidence to date. Future studies on the various subclasses of flavonoids will hopefully shed new light on whether particular subclasses have more prominent roles in CVD prevention than do other subclasses.
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