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Nutrient - Focus on Quercetin

By Cathy Robinson BScDipNutMed MBANT

It is often recommended that we eat plenty of different coloured fruit and vegetables every day. Apart from making our meals look artistic and taste delicious, there is a sound reason for this advice. Fruit and vegetable pigments are plant-based chemicals, known as phytochemicals, which play specific roles in the body, and possess amazing health benefits. The phytochemical, quercetin, belongs to a group of plant pigments known as flavonoids. Its name is derived from the latin quercetum, which literally translates as oak forest!

Flavonoids on the other hand get their name from the Latin word flavus meaning yellow. Flavonoids were originally referred to as Vitamin P.

Flavonoids are antioxidants – in other words, they mop up particles in the body known as free radicals, which would otherwise damage cells. Quercetin has been shown to have the greatest antioxidant activity amongst the flavonoids due to its ability to scavenge free radicals, particularly those that damage fats within the body.

Food sources of Quercetin

Foods rich in quercetin include onions, green tea, onions, apples, broccoli, spinach, red grapes, citrus fruit, tomato, raspberry, parsley, sage, blueberries and blackberries. Unfortunately foods can lose their quercetin content when cooked, especially when boiled, and if they are stored before eating. Onions, for example, have been found to lose as much as 33% of their quercetin when stored for twelve days.

Possible benefits of Quercetin

Quercetin has been the subject of numerous studies because of its promising health benefits.


In laboratory conditions, quercetin prevented immune cells from releasing histamines, the chemicals that cause allergic reactions such as hay fever, runny nose, watery eyes or hives. 

Immune System

Studies have reported that quercetin supplements reduced the incidence of upper respiratory tract infections following intense exercise.


Several laboratory studies show quercetin may have anti-inflammatory properties. It is believed to exert its effect by interfering with the production of chemicals, which cause inflammation such as prostaglandins and leukotrienes. Asthma sufferers, for example, have been found to have markedly higher levels of inflammatory leukotrienes than non asthma-sufferers.

High Blood Pressure

A study in 2009 found that quercetin reduced blood pressure in hypertensive and obese subjects.

Heart Disease and Elevated Cholesterol

Quercetin may have a role to play in atherosclerosis, in other words the plaque build-up in arteries. It appears to protect against the damage caused by cholesterol as well as prevent the build up of LDL cholesterol, which is a risk factor for heart disease.

In summary, the scientific interest in quercetin appears to be justified, so we may well be hearing more about this colourful character in the future. 

Article References

Quercetin & Blood Pressure Institute of Human Nutrition and Food Science, Department of Human Nutrition, Christian-Albrechts-University Kiel, Germany. 2009 Egert S, Bosy-Westphal A, Seiberl J, Kurbitz C, Settler U, Plachta-Danielzik S, Wagner AE, Frank J, Schrezenmeir J, Rimbach G, Wolffram S, Muller MJ Quercetin reduces systolic blood pressure and plasma oxidised low-density lipoprotein concentrations in overweight subjects with a high-cardiovascular disease risk phenotype: a double-blinded, placebo-controlled cross-over study. Quercetin and Immune System Med Sci Sports Exerc. 2007. Nieman DC, Henson DA, Gross SJ, Jenkins DP, Davis JM, Murphy EA, Carmichael MD, Dumke CL, Utter AC, McAnulty SR, McAnulty LS, Mayer EP. Department of Health, Leisure, and Exercise Science, Appalachian State University, Boone, NC To investigate the effects of quercetin supplementation on incidence of upper respiratory tract infections and exercise-induced changes in immune function. Trained male cyclists were randomized to quercetin or placebo groups and, under double-blind procedures, received 3 weeks quercetin (1000 mg a day) or placebo before, during, and for 2 weeks after a 3-d period in which subjects cycled for 3 hours a day at approximately 57% Wmax. Quercetin versus placebo ingestion did not alter exercise-induced changes in several measures of immune function, but it significantly reduced upper respiratory tract infection incidence in cyclists during the 2-wk period after intensified exercise.

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