They are responsible for the colors of many fruits and vegetables, are found also in grains, nuts, leaves and flowers, and studies suggest there value in the treatment of a number of disorders. They are considered one of the most common biological constituents in plants. They have a gentle, beneficial action on numerous physiological processes in the body and may benefit the heart, blood vessels, liver, immune system, connective tissue, adrenal glands, kidneys, musculature and nervous system.
Important herbs containing flavonoids include milk thistle, hawthorn, echinacea and bilberry.
Uncommon allergic reactions can occur, otherwise no significant side effects or interactions have been observed. Quercetin serves as the backbone for other flavonoids, and is the most active of the flavonoids. Many medicinal plants have a significant quercetin content. Although human studies are limited, its physiological actions explain its use in inflammatory and allergic conditions including asthma, hay fever, rheumatoid arthritis, lupus, diabetes and cancer. Sorbitol is implicated in the development of diabetic complications including cataracts, neuropathy and retinopathy.