Why Is Resveratrol Made From Japanese Knotweed When Everyone Talks About Grapes?

Resveratrol tends to bring one picture to mind: dark red grapes, grape skins and perhaps a glass of red wine. Then you turn over a supplement bottle and the ingredient panel says Japanese knotweed root.

How did we get from a vineyard to knotweed?

Japanese knotweed naturally contains resveratrol. Its underground parts, including the roots and rhizomes, are recognised botanical sources of resveratrol and related compounds, which is why Japanese knotweed is commonly used as a starting material for concentrated resveratrol extracts. Grapes genuinely contain resveratrol too. They are simply the source most people know best.

So a supplement using Japanese knotweed resveratrol is not swapping genuine resveratrol for a substitute. The plant is the starting source. What matters next is what the finished supplement actually provides. You can see that distinction clearly across our resveratrol supplements.

Grapes made resveratrol famous, but they do not own it

There is a good reason resveratrol is so closely connected with grapes. Resveratrol occurs naturally in grapevines, including in grape skins, and it is also found in wine. That familiar grape and red-wine story helped make the name resveratrol widely recognised.

But resveratrol is not exclusive to grapes. It occurs in multiple plant species, including Japanese knotweed, or Polygonum cuspidatum. That means the plant source people first heard about and the plant source used to make a concentrated supplement do not have to be the same.

It is also worth keeping the wine connection in perspective. Red wine may contain resveratrol, but drinking wine is not the same thing as taking a supplement, and we would not suggest alcohol as a way to get a particular amount of resveratrol.

The unexpected part of the story is underground

Japanese knotweed looks like an odd ingredient if you are still picturing grapes. The part that helps make sense of the label is below the soil.

Scientific analysis of Polygonum cuspidatum has identified resveratrol and related stilbene compounds such as polydatin in the plant. Studies comparing different plant parts have found that roots and rhizomes can contain much more of these compounds than leaves and stems. Research on fresh Japanese knotweed harvested in Japan also found only small amounts of resveratrol in the edible stem portions, with substantially larger amounts in underground parts.

That is why wording such as Japanese knotweed root, root extract or root/rhizome extract makes sense on a resveratrol label. The underground tissues are useful botanical starting material for concentrating the compounds manufacturers want to provide.

This does not mean the concentration is identical in every plant. Growing conditions, plant part, harvest timing and processing can all affect what is present. It simply explains why the root keeps appearing when you pick up a bottle of resveratrol from Japanese knotweed.

Why would a plant make resveratrol?

Resveratrol is described as a phytoalexin. In everyday language, that means it is one of the compounds plants can produce as part of their response to challenges such as pathogens and environmental stress.

Grapevines can produce resveratrol as part of those plant defence responses. Japanese knotweed can produce it too. The useful point here is botanical, not medical: resveratrol is a real plant compound found in more than one species.

A plant making more of a defence compound under certain conditions does not automatically make a supplement more powerful for you. Once we move from plant biology to a finished capsule, the label and formulation matter much more than the story of how the plant responded in the field.

A root extract is not the same thing as eating the root

Japanese knotweed root contains a mixture of plant compounds. A finished resveratrol supplement can be made from an extract in which selected constituents have been concentrated and purified. Published work has shown that resveratrol can be isolated from Polygonum cuspidatum, and other research has examined processing that converts some polydatin, a resveratrol glucoside, into free resveratrol.

That helps explain an important label detail. When you see Japanese knotweed root extract, it does not necessarily mean the capsule is simply filled with raw ground root. The botanical material can be a starting point for a more concentrated ingredient.

We would not assume that every product uses the same extraction method. Manufacturers may use different processes, and a research paper describing one method does not tell us how every commercial formula is made. For you, the practical question is simpler: after the plant has been processed, what amount and form of resveratrol does the finished label state?

Japanese knotweed tells you where it started, not where the numbers finish

Our current Solgar Resveratrol 100mg label is a useful example. Each vegetarian capsule lists Polygonum cuspidatum root 200 mg, providing resveratrol 100 mg at a stated 50% standardisation.

Those two numbers are doing different jobs. Polygonum cuspidatum root tells us the botanical source and amount of the source ingredient. The separate 100 mg figure tells us how much resveratrol that ingredient is stated to provide in the capsule.

That is why looking only for the words Japanese knotweed does not tell you the whole story. A source name can be useful, but the finished resveratrol amount still needs to be stated if you want to know how much the product provides. We also would not treat 100 mg as an automatic ideal amount. It is simply the amount stated for this particular formula.

Grapes and Japanese knotweed can even appear in the same bottle

The grape story and the knotweed story do not have to compete. Our current NOW Resveratrol 200mg label shows both in one formula.

Each vegetarian capsule lists 400 mg of Polygonum cuspidatum root/rhizome extract, providing 200 mg of trans-resveratrol. It also includes 10 mg of alcohol-free red wine extract from Vitis vinifera fruit, standardised for polyphenols.

So here Japanese knotweed supplies the stated trans-resveratrol, while a separate red-wine extract also appears in the formula. That is a neat reminder that a supplement can use one botanical source for a concentrated amount of resveratrol and include a grape-derived ingredient alongside it.

We do not need to turn that into a claim about synergy, absorption or better results. The label itself already tells the useful story: grapes and Japanese knotweed can sit comfortably in the same resveratrol product.

Why our resveratrol shelf can start with a root, not a vineyard

We know grapes and red wine are what many customers picture when they hear resveratrol. When Japanese knotweed appears on a current supplement label, we see it as useful source information rather than something contradictory. Japanese knotweed is an established botanical source of resveratrol.

The next thing we want to know is what the finished formula actually provides. With Solgar, the current label separates the 200 mg of Polygonum cuspidatum root from the 100 mg of resveratrol it provides. With NOW, Japanese knotweed root/rhizome extract supplies the stated 200 mg of trans-resveratrol, while a separate alcohol-free red wine extract is also included.

That is the kind of clarity we like when we look across our resveratrol range. We think a clear source story makes it easier to understand what you are buying, and that is worth looking for when you compare resveratrol supplements.

What the source can tell you, and what still needs checking

Japanese knotweed on the label tells you where the botanical ingredient came from. That is useful. It can help explain why a bottle that you expected to be grape-based has Polygonum cuspidatum root in the ingredients instead.

But origin does not automatically tell you the final resveratrol amount. It also does not tell you whether the product specifies trans-resveratrol or another form, how pure the finished ingredient is, whether independent testing has been done, how well the formula will be absorbed, what amount is right for you, or whether one supplement will work better than another.

Those are separate questions. Source is one piece of information, not the whole picture.

A quick safety note

We are talking here about finished supplements, not wild harvesting. We do not recommend collecting or eating wild Japanese knotweed as a substitute for a labelled product. If you choose a resveratrol supplement, follow the current product label. Check with a qualified health professional if you take medicines, are pregnant or breastfeeding, manage a health condition, or are unsure whether resveratrol is suitable for you.

Common questions

Why do resveratrol supplements use Japanese knotweed instead of grapes?

Japanese knotweed is commonly used because its roots and rhizomes are recognised natural sources of resveratrol and related compounds and can provide useful starting material for concentrated supplement extracts. Grapes contain resveratrol too, but they do not have to be the source used for a concentrated supplement ingredient.

Is Japanese knotweed the same thing as resveratrol?

No. Japanese knotweed is a plant, while resveratrol is one of the compounds found in that plant. A Japanese knotweed extract can contain resveratrol along with other plant compounds, so the source ingredient and the stated resveratrol amount are not automatically the same number.

Is resveratrol from Japanese knotweed different from resveratrol in grapes?

Resveratrol refers to the same chemical compound regardless of which plant supplied it. Finished extracts and supplements can still differ in isomer specification, concentration, other plant compounds, excipients and formulation, so the botanical source alone does not make two products identical.

Does Japanese knotweed contain more resveratrol than grapes?

There is no single universal number that makes this a useful yes-or-no comparison. Resveratrol levels vary with plant part, variety, growing conditions, harvest and analysis. Japanese knotweed roots and rhizomes are recognised as rich botanical sources used for extraction, while grapes are also genuine natural sources of resveratrol.

Which part of Japanese knotweed contains resveratrol?

Resveratrol has been identified in several parts of Japanese knotweed, but research has found higher levels in underground tissues such as roots and rhizomes than in many above-ground parts. That is why root or root/rhizome extract commonly appears on supplement labels.

Does Japanese knotweed on a label tell me how much resveratrol I am getting?

No. Japanese knotweed tells you the botanical source. To know the stated resveratrol amount, look for a separate resveratrol figure on the label, such as a line showing how much resveratrol the extract provides.

Can a resveratrol supplement contain both Japanese knotweed and grape extract?

Yes. A formula can use Japanese knotweed as its concentrated resveratrol source and also include a grape or red-wine extract for other polyphenols. Our current NOW Resveratrol 200mg is an example, with Japanese knotweed supplying the stated trans-resveratrol and a separate alcohol-free red wine extract also listed.

References

1. Hasan M, Bae H. An Overview of Stress-Induced Resveratrol Synthesis in Grapes: Perspectives for Resveratrol-Enriched Grape Products. Molecules. 2017. PubMed.
2. Yu S-h, Zha J-p, Zhan W-h, Zhang D-q. Contents comparison of resveratrol and polydatin in the wild Polygonum cuspidatum plant and its tissue cultures. 2006. PubMed.
3. Kurita S, Kashiwagi T, Ebisu T, Shimamura T, Ukeda H. Content of resveratrol and glycoside and its contribution to the antioxidative capacity of Polygonum cuspidatum harvested in Kochi. Biosci Biotechnol Biochem. 2014. PubMed.
4. Chen H, Tuck T, Ji X, et al. Quality assessment of Japanese knotweed grown on Prince Edward Island as a source of resveratrol. J Agric Food Chem. 2013. PubMed.
5. Wang D-G, Liu W-Y, Chen G-T. A simple method for the isolation and purification of resveratrol from Polygonum cuspidatum. J Pharm Anal. 2013. PubMed.
6. One-pot method based on deep eutectic solvent for extraction and conversion of polydatin to resveratrol from Polygonum cuspidatum. 2021. PubMed.

From the vineyard to the capsule

Grapes gave resveratrol its famous story. Japanese knotweed helps explain how concentrated resveratrol ends up in many supplement capsules.

The surprising ingredient panel is not really a contradiction at all. Japanese knotweed naturally contains resveratrol, and its roots and rhizomes are widely studied as sources of the compound. Once you know that, the useful question changes from why is there knotweed in this bottle? to what does this finished formula actually provide?

That is how we look at it too. Knowing the source is useful, but we still check the stated resveratrol amount and the rest of the formula before choosing.