Quercetin: The Flavonoid from Sophora Japonica

An apple with its skin, a raw onion, a handful of berries – all of these provide quercetin, one of the best-known plant flavonoids. But anyone looking for a concentrated supplement comes across an exotic name: Sophora Japonica, the Japanese pagoda tree. Why this plant of all things?

Quercetin is a flavonoid and a secondary plant compound. For concentrated food supplements it is usually obtained from the flower extract of Sophora Japonica, because this plant is particularly rich in quercetin – high-quality extracts are standardised to a high content (e.g. 98 %). Because pure quercetin is absorbed rather moderately, it is often combined with piperine.

To put things in context first: quercetin is a secondary plant compound for which no health claims are currently authorised in the EU. We describe its origin, properties and quality neutrally and without promising any effects.

What quercetin is – and where it is found

Quercetin belongs to the flavonoids, a large subgroup of secondary plant compounds. These are natural pigment and protective substances that plants produce, among other things, to defend against UV light and predators. In our diet quercetin is widespread: particularly rich sources are onions (especially the outer, intensely coloured layers), apples with their skin, capers, kale, berries and green tea. But because we only take in relatively small amounts through a normal diet, some people reach for a concentrated extract.

Sophora Japonica – the concentrated source

For a high-dose supplement it makes sense to fall back on a particularly quercetin-rich plant. The Japanese pagoda tree (Sophora Japonica) is exactly that: an extract can be obtained from its flower buds that is standardised to a high quercetin content – often to 98 percent. "Standardised" means that every batch is adjusted to the same defined content, so that you know how much pure quercetin is actually in your capsule. This transparency is a key quality feature.

Why piperine? The absorption question

Just as with curcumin, absorption is a recurring topic with quercetin too: on its own, pure quercetin (the aglycone) is utilised rather moderately because it is poorly water-soluble. A proven approach is combining it with piperine, the pungent compound from black pepper, which can improve absorption. We describe the same trick in detail in the guide Turmeric and curcumin. How and when it is best to take quercetin, and which substances it is otherwise combined with, you can read in the sister article Quercetin: Intake and Bioavailability. The basics of absorption are explained in Bioavailability simply explained.

Flavonoids – the family quercetin belongs to

To classify quercetin correctly, it helps to look at the large family of flavonoids. These are secondary plant compounds responsible for many colours in fruit and vegetables – from the yellow of onion skin to the deep red of berries. Within this family, quercetin belongs to the subgroup of flavonols and is one of the best-known representatives there. Plants do not produce these substances by chance, but as protection against UV radiation, predators and environmental stress. For us they are a natural component of a plant-rich diet: anyone who eats plenty of colourful fruit and vegetables automatically takes in a broad spectrum of flavonoids, in which quercetin is only one of many. That is precisely why we keep emphasising that a single supplement complements the variety of a good diet, but does not replace it.

Quercetin in the context of other plant compounds

Quercetin is rarely the only plant compound people are interested in. It is often mentioned together with other flavonoids and polyphenols. This overview places it in context:

Interesting: rutin, another well-known plant compound, is chemically closely related to quercetin and also often comes from Sophora Japonica. Anyone interested in the group of grape seed and bark extracts will find more in OPC from grape seed and pine bark, and on resveratrol in Resveratrol: Polyphenol from the grape.

What research is investigating

Quercetin is one of the most intensively studied flavonoids of all. Research is interested in its role as a secondary plant compound and especially in the question of how absorption can be improved – hence the many formulation and combination approaches. The chemical relationship between solubility and utilisation is well understood. Concrete health effects are still being researched and discussed; there are currently no health claims authorised in the EU for quercetin. We therefore stick to a factual description.

The Japanese pagoda tree – a portrait

Sophora Japonica, now botanically also called Styphnolobium japonicum, is a deciduous tree from the legume family. Originally native to East Asia, it is also planted as an ornamental tree in parks for its creamy-white flower panicles. For extract production the flower buds in particular are of interest, because they are especially rich in flavonoids – besides quercetin also in its relative rutin. The tree is thus one of the most productive plant sources for concentrated flavonoid extracts of all, which makes it the industry's standard raw material. The use of the flowers has a long tradition in East Asia and remains to this day the common basis of high-quality quercetin supplements.

How an extract is made

A crude extract is obtained from dried flower buds via a solvent process, which is then purified and concentrated until the desired quercetin content is reached. In an extract standardised to 98 percent, the powder consists almost entirely of pure quercetin. Standardisation is the decisive step: it is the only way to guarantee the same defined amount batch after batch. A reputable product clearly states this content and ideally proves it through an independent analysis. If a content declaration is missing entirely, that is a warning sign, because then you do not know how much pure quercetin is really in the capsule.

Dosage and intake

Quercetin supplements state their content in milligrams, for example 510 mg per capsule. It is often taken with a meal, ideally with a little fat. Stick to the dosage recommendation on the packaging. Detailed intake tips can be found in the article Quercetin: Intake and Bioavailability. For a rough guide on how to find a suitable amount at all, Adjusting dosage to body weight helps. If you add quercetin to your routine on a long-term basis, Creating an intake plan supports you.

What to look for in terms of quality

• Standardised quercetin content (e.g. 98 %) with a clear declaration per capsule.
• Defined source such as Sophora Japonica flower extract.
• Absorption-enhancing combination, for example with piperine.
• Lab-tested and preferably manufactured in Germany.
• Few fillers – how to recognise them is shown in Recognising additives and fillers.

Common questions before buying

Before deciding on a quercetin supplement, a few recurring questions come up. Is diet alone enough? For many people who eat plenty of onions, berries and apples, their diet already covers a good part of it – a supplement is then a deliberate additional choice. Is more better? No, a higher milligram value does not automatically mean more benefit, especially since absorption is limited and the form plays a bigger role than the number alone. And what should you look for on the label? The standardised content, the source, absorption-enhancing accompanying substances and a lab test. Anyone who checks these points makes an informed choice instead of being guided by maximum values on the packaging. Fundamental label tips are provided by Food supplements: reading the label correctly.

Honestly put in context

Quercetin from Sophora Japonica is a cleanly defined, easily standardisable plant compound – and that is precisely its strength: you know what is in it. What we may not and do not want to promise you is a concrete health effect, because authorised health claims are lacking for that. Used sensibly, quercetin is a supplement to a plant-rich diet, not a replacement. One more safety note: quercetin is considered well tolerated; when taking medication (including blood thinners), during pregnancy and breastfeeding, and with pre-existing conditions, check with a doctor beforehand.

Suitable products from Scheunengut

In the Quercetin category you will find high-dose capsules made from Sophora Japonica flower extract, some with piperine. If you would like to add vitamin C, take a look at Vitamin C. Related plant antioxidants are listed under OPC and Grape seed.

Frequently asked questions (FAQ)

Why is quercetin obtained from Sophora Japonica?

The Japanese pagoda tree (Sophora Japonica) is particularly rich in quercetin, which is why a highly concentrated extract can be obtained from its flower buds. Through normal foods we only take in relatively small amounts of quercetin. High-quality extracts are standardised to a defined content, often to 98 percent.

What does 'standardised to 98 %' mean for quercetin?

Standardised means that every production batch is adjusted to the same quercetin content. At 98 percent the extract consists almost entirely of pure quercetin. This ensures consistent quality and transparency: you know exactly how much pure quercetin is in a capsule.

What is the difference between quercetin and rutin?

Rutin is chemically closely related to quercetin – it is essentially a quercetin glycoside, that is, quercetin with an attached sugar residue. Both often come from Sophora Japonica. Rutin is present in bound form, while quercetin aglycone is the sugar-free base form that is more widespread as a concentrated supplement.

Is quercetin from Sophora Japonica suitable for vegans?

Purely plant-derived quercetin from Sophora Japonica flower extract is in principle vegan. What is also decisive is the capsule shell: look for a plant-based shell (e.g. HPMC) instead of gelatine. A glance at the ingredient list or a vegan note on the packaging provides clarity.