Quercetin is part of a group of plant pigments called flavonoids which are widely distributed in nature and give many fruits, flowers and vegetables their colour.
Foods naturally rich in quercetin include green and black tea, capers, apples, onions, broccoli, tomatoes, green leafy vegetables and berries.
Flavonoids, including quercetin, are antioxidants. These work by scavenging damaging particles in the body known as free radicals, which damage cell membranes, DNA, and even cause cell death. Antioxidants can neutralize free radicals and may reduce or even help prevent some of the damage they cause. They also help keep LDL from being damaged, which scientists think may contribute to heart disease.
Quercetin prevents immune cells from releasing histamines which cause allergic reactions. On that basis, quercetin may help reduce symptoms of allergies, including runny nose, watery eyes, hives, and swelling of the face and lips.
Antioxidants can be destroyed through heating and cooking of food.