Quercetin is one of the secondary plant substances (phytamine). Secondary plant substances come in a wide variety of chemical structures, each with specific properties. The best-known groups of phytochemicals include, for example, polyphenols, isoflavones and carotenoids. Quercetin belongs to the group of polyphenols and their subgroup, the (bio)flavonoids. There are over 5,000 different types of bio-flavonoids that occur naturally in plants. They are responsible for the flower and leaf color of the plant and for protection against UV radiation, predators, viruses, fungi and bacteria. Quercetin is the most common flavonoid and with its help other flavonoids can be built.
Quercetin is absorbed into the body via the (mainly small) intestine into the blood. According to current studies, a little less than half of the consumed amount is absorbed by the body and it takes up to nine hours after intake for the quercetin to be available to the body. The body does not store quercetin permanently, but excretes it again after about 35 hours. Therefore, quercetin should be administered regularly as part of therapy.
A high quercetin content is found, for example, in capers (per kg about 1600 mg quercetin), onions (per kg about 284-486 mg quercetin), chives (245 mg), cranberries (156 mg), black currants (69 mg) and in kale (60 mg).
Quercetin is mainly contained in the outer shells or layers of plants (e.g. in tree bark) and fruits (e.g. in grapes, apples, onions) to protect them from free radicals. Of course, this also means that almost no quercetin is absorbed if the outer shells are removed before consumption. For example, quince peels can contain up to 180 mg quercetin per kg. In the fruit body itself, on the other hand, hardly any relevant amounts of quercetin can be found. inside, however, only minimal quantities can be found. Approx. 20% of the quercetin is also found directly under the skin of onions and is therefore usually removed during skinning.
The cultivation method is also relevant for the quercetin content. For example, tomatoes from organic farming have ~ 80% more quercetin than those from conventional farming. In addition, heat during cooking can result in further quercetin losses (according to studies up to 25%).
Among the tree barks, that of the oak in particular stands out in terms of quercetin content, which also results in the name "Quercetin" - because "quercus" is the Latin name for "oak"; more precisely: for the dyer's oak (Quercus velutina). But over time, a very high quercetin content was also found in the bark of other tree species. The QIDOSHA quercetin is obtained from the Japanese cord tree (Sophora japonica), as its flower extract contains a particularly large amount of natural quercetin.
Benefit and mode of action
Since there have been hardly any scientific studies on quercetin in humans to date, so-called "health claims", i.e. health promises associated with taking it, are not permitted. The study situation therefore relates primarily to laboratory and animal experiments. However, since there are numerous promising starting points here, clinical studies on humans can be expected in the near future.
It is undisputed that quercetin appears to be a particularly strong antioxidant that is roughly comparable to OPC or the epigallocatechin gallate (EGCG) from green tea leaves. The reason for this can be found in the chemical structure of quercetin - because it is a polyphenol that has an additional hydroxyl group instead of a sugar molecule.And the more OH groups a polyphenol has, the higher its antioxidant effect
Another special feature of flavonoids such as quercetin is their ability to regenerate substances that have already been oxidized (e.g. vitamins C and E), i.e. to give them back their antioxidant power.
In a meta study from 2019 on the effect of quercetin in diabetes, researchers were able to find out on the basis of animal studies that doses of 10, 25 and 50 mg quercetin each kg body weight there was a significant difference between the mean values of the serum glucose level. https://pubmed.ncbi.nlm.nih.gov/30735748/
A Japanese study suggests that quercetin may have an antiallergic effect by inhibiting what is known as the histamine H1 receptor (H1R). The severity of allergy symptoms increases in proportion to the activity of this receptor. https://pubmed.ncbi.nlm.nih.gov/23333628/
A study by the University of Naples postulates an anti-inflammatory effect of quercetin in that it is in principle able to reduce concentrations of the tissue hormone prostaglandin E2 and the fatty acid derivative leukotriene B4. Both substances are relevant for the initiation of inflammatory processes and significantly involved in the release of inflammatory mediators such as histamine. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.2042-7158.1988.tb05250.x
A study from 2007 could have a blood pressure lowering effect. The volunteers were administered 730 mg of quercetin daily for almost a month and a reduction in systolic (−7 ± 2 mm Hg) and diastolic (−5 ± 2 mm Hg) blood pressure could be determined in patients with high blood pressure. Further clinical studies are therefore advisable. https://pubmed.ncbi.nlm.nih.gov/17951477/
How do I recognize a high quality product?
When buying, you should make sure that the product is 100% natural. The premium flower extract should come from the Japanese cord tree Sophora japonica and ideally have an extract ratio of 15:1. The water-alcohol extract used for production should be of high purity and contain no chemical solvents. Capsules can be perfectly integrated into your everyday life as a dietary supplement.
Legal consumer information
German and European case law wants to protect the consumer from supposedly misleading claims. The statements made here refer to the original Ayurvedic and TCM texts. This knowledge, which has been handed down for thousands of years, is based on experiences that are passed on from generation to generation. It should not be claimed that the products described here have any effect in the sense of western medicine. All products are dietary supplements; they are not medicines and have no medicinal effect. If you are ill and need medical care, please contact your doctor or pharmacist