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The prospective cohort study of 34 489 postmenopausal women, published in the current issue of the American Journal of Clinical Nutrition, reports that high dietary intake of several classes of flavonoids can reduced the risk of mortality from cardiovascular disease (CVD), coronary heart disease (CHD) and stroke by between 10 and 22 percent.
"This prospective study of postmenopausal women, with 16 years of follow-up, is, to our knowledge, the first study that has reported on total flavonoids and on seven subclasses of flavonoids," wrote lead author Pamela Mink from Washington-based Exponent Inc.
Flavonoids have been receiving interest with a mounting body of science, including epidemiological and laboratory-based, continuing to report the cancer-fighting potential of a number of different flavonoids, such as isoflavones, anthocyanidins and flavonols.
How the study was done
The new study used a 127-item food frequency questionnaire to collect dietary information on 34 489 postmenopausal women (average age 62 at baseline, average BMI 27 kg per sq. m). The researchers used the new US Department of Agriculture databases of food flavonoid content to calculated flavonoid intakes.
After 16 years of follow-up, Mink and her co-workers found that 7091 participants had died, including 2316 from combined CVD, 1329 from CHD, and 469 from stroke.
After adjusting for potentially confounding factors such as age, energy intake, smoking, and physical activity, and dividing flavonoid intakes into five intake groups (quintiles) the researchers report that the highest versus the lowest intake of anthocyanidins (0,2 vs. 0mg per day) was associated with a 10 percent reduction in total mortality, a 12 percent reduction in CHD and a nine percent reduction in CVD.
22% reduction in CHD
The highest vs. the lowest intake of flavanones (93,7 vs. 7,6mg per day) was significantly associated with a 22 percent reduction in CHD, and highest vs. the lowest intake of flavones (1,5 vs. 0,1mg per day) was significantly associated with a 12 percent reduction in total mortality.
The researchers also report that intake of apples, pears, and red wine was associated with lower CHD and CVD mortalities, while grapefruit intake was linked to lowered CHD mortality.
Interestingly, no significant benefits for cardiovascular health were observed for tea consumption, a flavonoid-rich food previously seen to have benefits.
"Results from this study suggest that the intake of certain subclasses of flavonoids may be associated with lower CHD and total CVD mortality in postmenopausal women," said the researchers. "Furthermore, consumption of some foods that are high in flavonoid content or that are among the main sources of flavonoids in the diet of these study participants may have similar associations."
Results not conclusive
Mink says, however, that these results cannot be considered conclusive and called for other prospective studies to replicate these findings.
The role of flavonoids as antioxidants was recently challenged by a review by scientists from the Linus Pauling Institute at Oregon State University. They reported that, while the compounds showed excellent antioxidant activity in the lab, they are rapidly metabolised in the body.
"This does not preclude the possibility that flavonoids may accumulate in tissues where they might exert local antioxidant effects or that very low concentrations of flavonoids may modulate cell signalling, gene regulation, antiogenesis, and other biological processes by non-antioxidant mechanisms, which may explain the purported health benefits of flavonoids," wrote Silvina Lotito and Balz Frei in the journal Free Radical Biology and Medicine. - (Decision News Media, March 2007)
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