A study by Bondonno et al found that moderate intake of flavonoids resulted in lower all-cause mortality, including cancer. Those in the highest one-fifth had a 17 percent reduced risk for all-cause mortality, a 15 percent reduced risk for cardiovascular disease death, and a 20 percent reduced risk for cancer mortality. The association peaked at about 500 milligrams of flavonoids a day, and was stronger for smokers, heavy drinkers and the obese.
From a New York Times article about the study: “Good sources of flavonoids include tea, chocolate, red wine, citrus fruits, berries, apples and broccoli. One cup of tea, one apple, one orange, and three-and-a-half ounces each of blueberries and broccoli would supply more than 500 milligrams of total flavonoids.”