Quercetin is the most abundant member of the flavonoid family of plant chemicals. It is a powerful antioxidant, anti-inflammatory and anti-histamine. There is some evidence that quercetin can assist in maintaining a healthy heart and blood vessels, reduce allergies and promote prostate and urinary tract health. Concentrated in apples, quercetin may well be responsible for an apple a day keeping the doctor away.
Healthy heart and blood vessels
Quercetin has been well studied as an agent for promoting healthy blood vessels. It has been shown to keep the muscular lining of arteries healthy and resilient by augmenting nitric oxide, a potent vasodilator that keeps artery walls relaxed, blood vessels open and blood pressure healthy.
Quercetin also helps to reduce a process known as platelet aggregation, which can result in blood clots. Intravenous injections of quercetin have demonstrated the ability to reduce heart damage caused by oxygen deprivation, improve heart function and increase survival rates after a heart attack.
Free radicals damage blood vessel walls and, as leaky blood vessels are not conducive to a long and prosperous life, your body deposits thick and sticky cholesterol over the damaged area just like a Band-aid on a scraped knee. Consuming adequate amounts of powerful antioxidants such as quercetin, which neutralise and mop up the damage caused by free radicals, can help to prevent cholesterol building up in your blood vessels.
Quercetin also helps to prevent the oxidisation of cholesterol. You’re probably already aware that LDL is considered the bad form of cholesterol, but oxidised LDL is far more dangerous — it literally transports free radicals directly to your blood vessels. Since it is such an effective antioxidant, diabetics are often encouraged to supplement or consume quercetin-rich foods to help prevent blood vessel damage caused by increased free radicals.
Quercetin also helps to stabilise collagen, which keeps your connective tissue and capillaries healthy. Quercetin is often included in formulations for varicose veins and poor circulation that results in swollen and aching feet and legs.
Quercetin and allergies
When histamine is released in the cells that line your nasal passages and respiratory tract, it causes them to become swollen and leaky, producing the range of symptoms familiar to any hay fever sufferer: blocked, stuffy nose, swollen, itchy and watery eyes, blotchy skin, coughing and sneezing. Quercetin seems to have an anti-histamine effect and seasonal allergy sufferers can take up to 350mg–650mg of quercetin three times a day. Unlike anti-histamine medications, quercetin doesn’t cause side-effects such as drowsiness associated with using Quercetin.
A double blind, placebo controlled study (Techniques in Urology Journal) on a group of men with chronic prostatitis showed that a supplement containing quercetin with small amounts of bromelain and papain included to enhance absorption, improved symptoms in 82 per cent of the group taking the quercetin during the one month trial. Chronic prostatitis is caused by inflammation and swelling of the prostate gland producing pelvic pain, difficult and painful urination along with lowered libido. The dosage of quercetin used in the study was 500gm twice daily for one month.
Painful bladder syndrome
Painful bladder syndrome or interstitial cystitis is a debilitating condition for which conventional medical treatment is mostly ineffective. Symptoms are similar to a urinary tract infection, however no infection is present. Chronic inflammation of the urinary tract and bladder produce painful, burning urination; pelvic pain and the constant urge to urinate. Ninety per cent of sufferers of painful bladder syndrome are women. A 2001 (Urology) study showed that 500mg of quercetin twice daily for 4 weeks reduced symptoms with no side effects and a larger 2008 (Canadian Journal of Urology) study on 252 patients found that a supplement providing 600mg of quercetin daily along with glucosamine and chondroitin sulphate was also effective at reducing symptoms.
Laboratory studies have shown that quercetin may have potent anti cancer potential. Preliminary trials have indicated that it may prevent tumour growth, however human studies are sorely lacking. There is limited evidence that quercetin may be beneficial for lung and pancreatic cancer. It is unlikely that oral doses of quercetin including supplemental forms would be sufficient to inhibit tumour growth in active cancer. However, quercetin is found in many of the foods that are linked to lowered rates of cancer so a quercetin rich diet makes for good preventative medicine.
Quercetin is a very safe supplement. No toxicity has been reported with oral doses of up to four grams, though doses of this level should be taken with the guidance of a health professional. Although quercetin has demonstrated mutagenic properties to cells in test tubes, most studies have indicated that quercetin does not induce cell mutations or result in cancer in vivo, ie in living animals or human beings.
Where can I find quercetin?
Quercetin is found in the following foods:
- Green tea
- Onions, especially red onions, concentrated in the outer layers
- Red grapes
- Tomato (organically grown tomatoes may contain up to 79 per cent more quercetin than non-organic)
Until very recently, quercetin was thought to be poorly absorbed, based on a 1975 report, but quercetin is often combined with bromelain in supplements to help improve absorption. Being water-soluble, quercetin is quickly metabolised and excreted; in fact, 96 per cent is believed to be excreted within 72 hours of taking it, so you’ll need to take it daily, especially in the case of allergies, to achieve best results.