Quercetin is a member of the bioflavonoid family- a group of plant pigments that are responsible for the colours of many fruits and flowers. Research suggests flavonoids may be useful in the treatment of many health conditions discussed later on. Quercetin is commonly found in the skins of apples and red onions. There is no established Recommended Daily Amount (RDA) for Quercetin however the recommended dosage range for Quercetin is 200-400mg before meals.
Quercetin works synergistically with vitamin C to aid in several functions in the body. Together, they help protect and preserve the structure of capillaries. Quercetin also works with vitamin C to help reduce histamine levels. Histamine is the hormone released by the body in response to exposure to allergens and is responsible for the symptoms which occur. Quercetin has also been shown to have antibacterial and antioxidant properties and helps to promote circulation.
Deficiency of flavonoids can manifest itself as symptoms of scurvy, characterised by bleeding gums, poor wound healing and extensive bruising.
Allergies and Asthma– Both Quercetin and Vitamin C have been shown to be an effective treatment for allergies and inflammatory disorders such as asthma and hay fever (1).
Anti-inflammatory agent-To evaluate the role of Quercetin as an antioxidant and anti-inflammatory agent, a randomized double-blind clinical trial was undertaken to determine the effects of quercetin supplementation on oxidative stress and inflammatory biomarkers in nonprofessional athletes with regular exercise over a period of 8 months. The results confirmed that after 8 weeks supplementation with quercetin-vitamin C there was a reduction in oxidative stress and markers of inflammation (2). Furthermore, in other studies, quercetin was reported as a long-lasting anti-inflammatory substance that possesses strong anti-inflammatory capacities (3), (4).
Chemo-preventative– As well as its inflammatory effects, quercetin is also reported to have chemopreventive effects (5). Studies in animal have shown its ability to potentiate the antitumor effects in liver cancer cells while protecting normal liver cells (6).
Cancer- Research suggests quercetin may also be beneficial in patients with pancreatic cancer. A study on mice showed quercetin inhibited the growth of pancreatic cancer cells (7).
Depression- Quercetin has also demonstrated neuroprotective and antidepressant effects (8) and exerts pro-oxidant effects by decreasing homocysteine levels (9).
Allergies– Quercetin is a natural anti-histamine and so may help to relieve allergic-symptoms of hay fever and asthma symptoms.
Reducing inflammation– Quercetin may help to relieve the swelling associated with ailments such as arthritis.
Reducing the risk of heart disease– Quercetin may have antioxidant properties which have historically helped to prevent arteriosclerosis (hardening of the arteries).
Quercetin is considered to be well tolerated in humans with no side effects reported even when consumed at high doses (2,000mg per kg body weight). Allergic reactions are very uncommon however as with all compounds allergic reactions can occur and discontinuation would be advised. No Tolerable Upper Intake Level has been established for Quercetin.