Quercetin is a phytochemical found in onions, apples, tea, asparagus, blueberries and more. This flavonoid may have some anti-cancer benefits such as controlling abnormal cell growth and deactivating carcinogens, according to some lab studies.
But a recent laboratory study raises concerns that quercetin, in larger doses, may act differently and actually aggravate cancer in some cases. In this study, researchers gave quercetin and another antioxidant (ferulic acid) to severely diabetic laboratory rats. They found that these rats developed more advanced forms of kidney cancer.
Although a lab study, the results do show the potential that too much of a good thing, including quercetin, may not be better – or even helpful.
AICR does not recommend dietary supplements for cancer prevention. Of course there are special situations where supplements are valuable for other reasons, but so far evidence does not confirm that, for the general population, supplements are helpful for preventing cancer.
In addition to quitting smoking, the best thing you can do to lower your cancer risk is to maintain a healthy body weight, get at least 30 minutes of moderate physical activity daily and eat a plant-based diet with plenty of vegetables, fruits, whole grains and legumes for an abundant variety of healthful plant compounds and more.