Flavonoids, a class of antioxidants found in tea, red wine, soybeans, fruit and vegetables, are the focus of increasing study since oxidative stress has been linked to an increased risk of various diseases including cancer, Alzheimer's, and cardiovascular disease.
The first of two presentations at the meeting by Brian Fink and colleagues from the University of North Carolina, reported the results of a case-control study of 1,434 women with breast cancer and 1,440 healthy women.
Post-menopausal women who consumed the most flavonoids were associated with a 45 per cent lower risk of breast cancer, compared to women who consumed the least. No such link was found for pre-menopausal women.
For specific flavonoids, the most protection from breast cancer appeared to come from flavones (39 per cent risk reduction), lignans (31 per cent risk reduction), and flavan-3-ols (26 per cent).
"These results are consistent with other studies conducted among Mediterranean women," said Fink.
"Few epidemiologic studies have examined whether there is a relationship between breast cancer and dietary flavonoids. Our study proposes that dietary flavonoids can help American post-menopausal women reduce their risk of breast cancer," he said.
Fink stressed that there are no recommended dietary standards for ingestion of flavonoids, and that there was still a lot of uncertainty as to how these compounds worked on a cellular level.
"Minute differences in chemical structure could determine how a certain natural antioxidant may work to prevent disease, including cancer. More study is needed to determine why certain flavonoids appear to be effective at reducing cancer risk, and others do not appear to have these properties," said Fink.
More study after positive preliminary results was also the conclusion of a presentation by Margaret Gates from Harvard University.
Gates reported the results of an epidemiological study of 66,384 women from the Harvard Nurses' Health Study, which has been collecting health data for over 30 years.
"This is the first prospective analysis of flavonoid intake and ovarian cancer incidence," said Gates.
Flavonoid intake was calculated from food frequency questionnaires (FFQs) completed by the women in 1984, 1990, 1994 and 1998. During the following 18 years 344 confirmed cases of ovarian cancer were diagnosed.
For total flavonoid intake, the women who consumed the most were associated with a 22 per cent lower risk of ovarian cancer, a disease that accounts for 4 per cent of all cancers diagnosed in women globally, with 190,000 new cases every year.
"The associations were stronger when exposure was defined as cumulative average flavonoid intake over a period of 14 years, which suggests that long-term intake of flavonoids may be important," she said.
Significantly, Gates and her colleagues found that the flavonoid kaempferol, found in caffeinated tea, broccoli and kale, was associated with 38 per cent reduction in the risk of ovarian cancer.
"Because this is one of the first studies of the topic, this association needs to be evaluated in another prospective study population before conclusions can be made," stressed Gates.
"However, if confirmed, consumption of flavonoids would provide another means for women to decrease their risk of ovarian cancer."