What is Quercetin?
Quercetin is a bioflavonoid and a natural pigment found in numerous foods. Onions and grapes are the best
food sources of quercetin (1). Quercetin’s unique properties allow it to interact synergistically with other
bioflavonoids, and it may improve the absorption of other supplements as well.
Quercetin is an effective antioxidant, and it scavenges free radicals. Free radicals can damage cells and
cause oxidative stress. Antioxidants prevent free radicals from accumulating and causing health problems
(2). Quercetin also has anti-inflammatory properties and helps support the immune system (3, 4).
Quercetin and Zinc
Quercetin and zinc working together may help
strengthen immune function (8, 9). Quercetin may act as a zinc-ionophore, which increases concentrations of
zinc. Ionophores bind to ions and transport those ions across cell membranes. Ionophores often have
antibacterial properties (10). Zinc plays a significant role in the immune system (11). Zinc deficiency
reduces antibody production, which makes the body more susceptible to infections (12, 13). However, it’s
difficult for zinc to distribute throughout cells (14). Quercetin acts as a zinc transport mechanism to
increase cellular zinc concentrations (8, 9).
Zinc plays a significant role in the immune system (11). Zinc deficiency reduces antibody production, which
makes the body more susceptible to infections (12, 13). However, it’s difficult for zinc to distribute
throughout cells (14). Quercetin acts as a zinc transport mechanism to increase cellular zinc concentrations
Quercetin and Vitamin C
Like quercetin, vitamin C is a potent
antioxidant that supports the immune system (15). Vitamin C also improves iron absorption, which is critical
for vegetarians and vegans as meat is a significant iron source (16). Vitamin C’s antioxidant properties
help strengthen the skin, which may improve the body’s defenses against infection (17). Quercetin and
vitamin C synergize to enhance their antiviral potential (15). Vitamin C recycles quercetin to increase its
Did You Know?
Quercetin works synergistically with saponins and may enhance their anti-inflammatory properties (5).
Saponins are a naturally occurring compound found in tea plants and tea extracts (6).
Quercetin also synergizes with green tea catechins. Green tea has four primary catechins, but the most
potent is EGCG. Taken together, quercetin and green tea extract may
improve exercise performance (7).
Quercetin and Resveratrol
Quercetin and resveratrol are both polyphenols
with anti-inflammatory properties (18). Resveratrol comes from a variety of plant sources including grapes,
raspberries, plums, and grape tomatoes (19). Wine is another rich source of resveratrol and contains high
amounts of quercetin as well (20). Combining these two antioxidants enhances their anti-inflammatory
What Are the Side Effects of Quercetin?
Quercetin is present in many foods and the FDA granted it GRAS (generally recognized as safe) status (22).
Typical doses do not cause side effects, but studies using larger doses up to 1g may cause a tingling
sensation, mild headache, or mild stomach aches (23). However, it’s important to note that quercetin may
interact with some medications. Always consult your doctor before starting any new supplement.
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