Human studies suggest naturally occurring plant antioxidants known as flavonoids―which contains a variety of subclasses, including flavonols, flavones, and flavanones―may reduce the risk of several age-related chronic diseases, including cancer. Current research with animal models and human studies suggest flavonoid intake may protect against cancer through several biological mechanisms. However, to date, the epidemiologic studies have yielded inconsistent results.
U.S. researchers investigated the association between dietary intake of certain flavonoids and flavonoid-rich foods and risk of cancers in the Women's Health Study. They identified 3,234 cancer cases among 38,408 women aged 45 years and assessed their intake of the flavonols quercetin, kaempferol, and myricetin, the flavones apigenin and luteolin, and foods high in these phytochemicals, such as tea, apple, broccoli, onion and tofu, by using food-frequency questionnaires.
A statistic analysis of the data showed no significant association between intake specific flavonoids, or of flavonoid-rich foods, and the incidence of total and site-specific cancers. This led the researchers to conclude these five common flavonols and flavones, or selected flavonoid-rich foods, did not play a major role in cancer prevention.