Quercetin extracted from a non-citrus source and other bioflavonoids extracted from lemon are found in the classical bioflavonoid group of nutritional supplements. They have been shown to support the integrity of mast cells, which play a key role in controlling the release of histamine. Bioflavonoids potentially support the health of the vascular system. Quercetin may also reduce the production of prostaglandins and leukotrines.