Bioflavonoids are a group of organic compounds that occur naturally in plants. They are responsible for giving fruits and vegetables their bright colors, such as red, yellow or blue pigments. Bioflavonoids have antioxidant properties which help to protect the body against damage from free radicals. They also play a role in strengthening blood vessels and improving circulation. Some common bioflavonoids include quercetin, rutin, and hesperidin.