Possible health benefits: anti-carcinogenic, anti-inflammatory, antiviral, antioxidant, psychostimulant, capillary permeability, mitochondrial biogenesis, SIRT1 boosting

Quercetin is a natural product reputed and used traditionally for its beneficial effects on health. It is categorized as a flavonol, one of the six subclasses of flavonoid compounds. The name Quercetin is derived from quercetum (oak forest), after Quercus. Quercetin has unique biological properties that offer potential benefits to overall health and disease resistance, including anti-carcinogenic, anti-inflammatory, antiviral, antioxidant, psychostimulant activities, capillary permeability, stimulation of mitochondrial biogenesis and boosting SIRT1. Quercetin is present in various vegetables as well as in tea and red wine. In a typical Western diet the daily intake of quercetin is estimated to be in the range of 0 and 30 mg.

Quercetin is also one of the most complex flavonol compounds to understand due to its metabolism. It involves intestinal uptake and/or deglycosylation, glucuronidation, sulfation, methylation, possible deglucuronidation and so on. From the various quercetin metabolites generated in the body it has been recently demonstrated that quercetin “3-O-β-D-glucuronide (Q3GA)” and quercetin “3′-sulfate” are the dominant quercetin conjugates in human plasma. Typically, the human quercetin plasma concentration is in the order of nanomolar, but upon quercetin supplementation it may increase upto the low micromolar range. This together with a half-life of the atom and its metabolites in the range of 11-28h it can be assumed that continuous supplementation leads to an  increased plasma concentration.

In human studies, quercetin has been mostly well tolerated. Doses up to 1,000 mg/day for several months did not produce adverse effects on blood parameters, liver and kidney function,hematology, or serum electrolytes. In general, there is plentiful available evidence that support the safety of quercetin for addition to food. A few items should be noted however. At high dosing, quercetin has been shown to inhibit topoisomerase II which is an essential enzyme in DNA replication and inhibition leads to diplochromosomes. These results have led to some  questioning the usefulness of quercetin as this introduces for example a possible risk of liver cancer while other studies find that this same property has anti-cancer treatment qualities. The second note is with regards to other drug interactions. Due to is complexity it may interfere with these prescription medications.

Therefore, it is great to see the continuing research into characterizing the promising benefits and also potential side effects of this novel dietary supplement.