Quercetin

Quercetin belongs to the flavonol subclass of polyphenols, distinct from the catechin family that dominates green tea research. While present in smaller quantities than catechins, quercetin and its glycosides (quercetin-3-glucoside, quercetin-3-galactoside, and rutin) contribute meaningfully to tea's overall bioactive profile. Interestingly, black tea contains more free quercetin than green tea because oxidation breaks glycosidic bonds, releasing the aglycone form. Quercetin is one of the most studied dietary flavonoids, with research supporting anti-inflammatory effects through inhibition of NF-kB and COX-2 pathways. It also exhibits antihistamine properties by stabilizing mast cells, which has made it popular as a natural supplement for allergy sufferers. In tea, quercetin works synergistically with catechins and other polyphenols, a phenomenon known as the food matrix effect — the combination of compounds in whole tea may be more effective than any isolated component. Black tea provides approximately 2-3 mg of quercetin per cup, while green tea provides 1-2 mg. Regular consumption contributes meaningfully to daily flavonol intake, supporting cardiovascular and immune health.