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 powerful anti-inflammatory effects, acts as an antihistamine, and helps reduce viral activity. As an antioxidant, it may help to prevent heart disease 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 (RSV). 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; through this function, along with its antioxidant properties, it may help in the prevention and treatment of infections and other diseases. It may be helpful against bacterial, viral and fungal diseases.