But certain flavonoids are thought to reduce the risk of heart disease and cancer, boost the immune system, protect against inflammation and allergic reactions, and act as anti-viral agents. One of the best known flavonoids is quercitin, found in apples, onions, red wine, black and green tea, green leafy vegetables, beans and citrus fruits. Laboratory tests have shown that quercitin may help prevent prostate cancer by blocking the hormonal activity which triggers the disease in men. About 500 known flavonoids belong to an important group called anthocyanins. These potent antioxidants provide the red and purple pigments that colour fruits and vegetables such as blueberries, grapes and red cabbage.
Red wine is especially rich in anthocyanins.
A large number of other biologically active compounds in fruits and vegetables also benefit health. Carotenoids, responsible for orange and yellow colours, are believed to reduce the risk of some cancers, as are glucosinolates which are especially abundant in broccoli. Research suggests that lycopene, mostly found in tomatoes, protects against prostate and some other cancers, heart disease and diabetes. Resveratrol adds to the healthy reputation of red wine by reducing the risk of heart disease. Some plant chemicals weakly mimic the female sex hormone oestrogen, and appear to alleviate menopausal symptoms.