Some quercetin supplements are derived from citrus fruits. Natural foods retailers and pharmacies sell quercetin supplements that come from non-citrus sources; these supplements are for those with citrus allergies. Quercetin supplements are sold as tablets or capsules. The supplements are available in water-soluble forms such as hesperidn-methyl-chalcone or quercetin-chalcon.
Quercetin Bioflavonoids
Quercetin is a bioflavonoid plant pigment that dissolves in water. Bioflavonoids have antioxidant properties in test tubes, and antioxidants help neutralize free radicals that can cause cell damage. Test-tube research has lead to the hypothesis that bioflavonoids have the same effects in humans, but the NYU Langone Medical Center states that there is growing evidence that this is not the case. Quercetin is found in many fruits, flowers and vegetables. Non-citrus quercetin is derived from sources other than citrus fruit.
Quercetin and Immune Response
Quercetin has antihistamine and anti-inflammatory properties. It works to counteract the effects of inflammation. Inflammation occurs when your body senses a threat and releases histamine; this causes your blood-vessel walls to become more porous. White blood cells and fluids exit the blood vessels and flood the affected area. The immune system sometimes mistakenly responds to a substance that is not harmful by releasing histamine and causing inflammation. This is an allergic response. UMMC states that quercetin is thought to mediate allergic reactions by preventing the release of histamine, but this has not yet been conclusively proven by research.
Other Benefits
Quercetin has been shown to reduce high blood pressure, prevent damage to LDL cholesterol, reduce the symptoms of interstitial cystitis and prostatitis and inhibit the growth of cancer cells, according to UMMC. The research that produced these finding has not been confirmed by additional studies.
Safety
The quantities of quercetin consumed from food are generally safe, according to the American Cancer Society. Higher than normal dosages of quercetin supplements may cause nausea. There have been no studies to ascertain whether the use of quercetin is safe for women who are pregnant or breastfeeding.
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