A flavonoid and lignan-rich diet may reduce the risk of developing breast cancer in postmenopausal women by about 35 percent, suggests a new study.
The research, led by Brian Fink from the University of North Carolina, focused on the dietary intakes of flavonoids, lignans and isoflavones by 1 434 women with breast cancer and 1 440 health controls in Long Island, New York, and supports previous findings from Greece and Italy.
While significant risk reductions were observed for high intakes of flavonols, flavones, flavan-3-ols and lignans among postmenopausal women, no beneficial affect was observed for isoflavones, nor for any of the nutrients among pre-menopausal women.
Certain women reap greater benefits
Writing in the American Journal of Epidemiology, Fink and his colleagues report that the effects of flavones and flavonols were most significant among the postmenopausal women with oestrogen-receptor (ER) positive and progesterone-receptor (PR) positive tumours.
"The ER-positive, PR-positive tumour receptor type is the most common type diagnosed among breast cancer patients in the United States," wrote Fink. "Thus, if replicated in other studies, our findings may be of public health significance."
How the study was done
The cases and controls completed food frequency questionnaires to assess their average intake for the previous 12 months, and the researchers report a significant decrease in breast cancer risk was associated with total flavonoid intake and lignan intake.
For postmenopausal women with an average intake of flavonols of more than 15,2 mg/day the risk of breast cancer was calculated to be reduced by 46 percent, compared to women with a daily intake of up to 3,7 mg/day.
The risk of breast cancer was also reduced for flavones by 39 percent (intakes of at least 0,22 mg/day compared to less than 0,04 mg/day), flavan-3-ols by 26 percent (at least 264,2 mg/day versus less than 5,1 mg/day), and lignans by 31 percent (at least 9,4 mg/day versus less than 2,0 mg/day).
"In this analysis, inverse associations with breast cancer risk were found for intake of total flavonoids and for most flavonoid classes," wrote Fink. "The associations were most evident in postmenopausal women."
The reason that no significant risk reduction was observed in the premenopausal women, said the researchers, is perhaps due to the anti-oestrogenic effects of the flavonoids being ineffective in the highly oestrogenic environment of this age group, but they do appear effective in the low-oestrogen environment of post-menopausal women.
"Further research based on large numbers of both premenopausal women and postmenopausal women is needed to help clarify this issue," they said.
Severable notable limitations
The study does have several notable limitations, including the reliance on the food frequency questionnaire for dietary recall over the course of one year, which is subject to recall error. The researchers also note that it is unknown if such questionnaires can accurately reflect dietary patterns during the time periods that are significant for the development of cancer.
Interest in flavonoids is growing rapidly and a mounting body of science, including epidemiological, laboratory-based and randomised clinical trials, continues to report the cancer-fighting potential of a number of different flavonoids, such as isoflavones, anthocyanidins and flavonols. - (Decision News Media, February 2007)
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