Reporting in the 20 April issue of the International Journal of Cancer (vol 114, issue 4, pp 628-33), researchers from the Harvard School of Public Health in Boston said that while they found no overall association between intake of flavonols and risk of breast cancer,"there was an inverse association with intake of beans or lentils that merits further evaluation".
Animal and in vitro studies have linked the antioxidant flavonols with a reduced risk of breast cancer but there is little epidemiological evidence to date to support these findings.
The US researchers analyzed data from 90,630 women who participated in the Nurses Health Study II, selecting women who were aged between 26 and 46 years old when the study began in 1991.
After an eight-year follow-up, the researchers saw no evidence of reduced incidence in breast cancer for those consuming the most flavonols. Nor was there any associations between individual flavonols such as kaempferol, quercetin and myricetin and risk of the disease.
However, further analysis suggested a possible benefit for bean or lentil consumption. Women who consumed beans or lentils at least twice a week were 24 per cent less likely to develop breast cancer than women who consumed them less than once a month.
Other major sources of flavonols include tea, onions, apples, string beans, broccoli, green pepper and blueberries. Some of these foods have been linked to reduced cancer risk, thought to be a result of certain antioxidant compounds.