Polygonum Cuspidatum (Japanese Knotweed): The Resveratrol Source

What is Polygonum cuspidatum?

Japanese knotweed is a tall, fast-spreading perennial in the buckwheat family (Polygonaceae) with hollow stems that can top 4 meters (13 feet). Its folk names in North America include Japanese bamboo and Mexican bamboo. It is native to Asia and was brought to North America in the late 1800s as a garden ornamental (USDA Forest Service, Fire Effects Information System).

It became one of the continent's most stubborn invasive weeds. Up to two-thirds of its mass sits underground in rhizomes that can reach 2 meters (about 7 feet) down, and a rhizome piece as short as 2 cm can sprout a new plant. In California it turns up along streams, in wetlands and at forest edges (USDA FEIS).

The same root has a long medical history in Asia. As hu zhang, the dried root appears in China's official pharmacopoeia and is usually paired with other herbs in traditional formulas (Zhang et al., Evidence-Based Complementary and Alternative Medicine, 2013). Reviews count more than 67 identified compounds in the plant, including stilbenes such as resveratrol and quinones such as emodin (Peng et al., Journal of Ethnopharmacology, 2013).

Why knotweed is the main resveratrol source

Resveratrol is a polyphenol that some plants make in response to stress, injury or fungal attack. Grapes, red wine, peanuts and blueberries contain it, but in small and unpredictable amounts. In grapes it sits only in the skins, and red wine's content swings with grape variety, region and how long the juice sat on the skins (Linus Pauling Institute, Oregon State University).

Knotweed root is far richer. The Linus Pauling Institute (LPI) reports that most resveratrol supplements in the US use extracts of Polygonum cuspidatum root. Root tissue holds much more resveratrol than stems or leaves, along with polydatin (a resveratrol molecule bound to glucose) and the anthraquinones emodin and physcion (Chen et al., Journal of Agricultural and Food Chemistry, 2013). Grape and red wine extracts are also sold, and some products blend the two.

Trans-resveratrol vs cis-resveratrol

Resveratrol exists in two shapes, called trans and cis. Light can flip the trans form into the cis form; in one lab test, long UV exposure converted about 60% of a trans-resveratrol sample (Figueiras et al., Journal of Fluorescence, 2011). Those authors note that trans-resveratrol is the better-studied form, while little is known about how cis-resveratrol behaves in the body. When a label says trans-resveratrol, it is naming the better-studied form.

What does the research on resveratrol show?

Lab and animal studies show many effects. Human results are less convincing:

• Low bioavailability. People absorb resveratrol well, but the body rapidly converts it to sulfate and glucuronide forms and clears it, so little unchanged resveratrol reaches the blood (LPI).
• Heart risk markers. A meta-analysis of 10 randomized trials found no meaningful effect on C-reactive protein, cholesterol, triglycerides, glucose or blood pressure (Sahebkar et al., International Journal of Cardiology, 2015).
• Blood pressure. Another meta-analysis of 6 small trials (247 people) found no overall effect; only a subgroup taking 150 mg a day or more showed lower systolic pressure, and the authors asked for better trials (Liu et al., Clinical Nutrition, 2015).

LPI's bottom line: no one yet knows of a resveratrol dose that is both safe and effective for preventing chronic disease. For other supplements with heart-health interest and stronger human data, see our guides to CoQ10 and red yeast rice.

Japanese knotweed and Lyme disease

Japanese knotweed is one of the herbs that appears in herbal regimens some people use for lingering symptoms after Lyme disease. The research behind that is a laboratory study: in test tubes, a knotweed extract was among the more active of 12 botanicals against the Lyme bacterium, Borrelia burgdorferi (Feng et al., Frontiers in Medicine, 2020). It did not wipe out the bacteria in follow-up cultures, and no human trial has tested it. Lyme disease should be treated by a physician.

Side effects and who should avoid it

• Digestive upset. Doses above 1,000 mg a day of resveratrol have caused nausea, gas, stomach pain and diarrhea (LPI). Whole-root knotweed products can also carry emodin, a compound found in many laxative herbs (Wang et al., Drug Metabolism and Disposition, 2001), in the same family as the anthraquinones in senna. A review links emodin to liver, kidney and reproductive toxicity at high doses with long-term use, based mainly on animal data (Dong et al., Phytotherapy Research, 2016).
• Bleeding. Resveratrol slows platelet clumping in lab tests, so high doses might raise bleeding risk alongside warfarin, heparin, clopidogrel, aspirin or other NSAIDs (LPI; Memorial Sloan Kettering Cancer Center).
• Other medications. At 1 gram a day, resveratrol changed the activity of several liver enzymes that process drugs, which could alter drug levels (MSKCC).
• Estrogen-sensitive conditions. Resveratrol can act like a weak estrogen in some cell studies. LPI advises women with a history of breast, ovarian or uterine cancer to avoid resveratrol supplements.
• Pregnancy and breastfeeding. Safety has not been established, so skip it (LPI).

Find it at William's

We don't sell knotweed root itself; we carry resveratrol supplements. Here is what each product's online description says about its source:

• Reserveage resveratrol 250 mg, 30 capsules: the only one whose description names a plant source. It mentions a blend that includes wildcrafted Japanese knotweed and organic muscadine red wine grapes.
• Now resveratrol 200 mg, 60 veg capsules: made with grape seed extract; the description does not name the resveratrol source.
• Source Naturals resveratrol 500 mg, 60 tablets: a higher-dose tablet; source not stated online.
• Country Life Resveratrol Plus, 120 vegicaps: source not stated online.

If the source matters to you, read the ingredient list on the bottle in the store or ask us to check it for you.

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