Quercetin is a bioflavonoid that is commonly found in red apples and red onions. Combined with Vitamin C, bioflavonoids work to rebuild small blood vessels and other structural parts of the body. Quercetin has been shown to have powerful anti-inflammatory effects, act as an antihistamine, and help reduce viral activity. As an antioxidant, it may help keep the heart healthy by protecting LDL cholesterol from becoming damaged, which cardiologists believe is the underlying cause of heart disease. Quercetin may also block an enzyme that leads to accumulation of sorbitol, which has been linked to nerve, eye and kidney damage in people with diabetes. Quercetin is a potent natural reverse transcriptase blocker.
Though large doses may be required in humans to produce therapeutic effects, quercetin has been shown to have antiviral activity against HIV, herpes simplex, polio-virus and the respiratory syncytial virus. One study even showed that it was possible to overcome the polio virus by pairing vitamin C with quercetin. Vitamin C is an antioxidant vitamin, which helps prevent oxidation of water-soluble molecules that could otherwise create free radicals. It also acts as a stimulator to the immune system and may be helpful against bacterial, viral and fungal diseases.