Japanese knotweed extract root. Polygonum cuspidatum is a large, herbaceous perennial plant native to eastern Asia. Its root extract, huzhang, is a traditional Chinese medicine. Japanese knotweed was first introduced to Europe and North America in the late 19th century. Today it is a commercial source of resveratrol for dietary supplements.
Resveratrol is a naturally occurring antioxidant compound that is also abundant in the vines, roots, seeds and stalks of grape plants. Wine contains resveratrol—a glass of red wine delivers about 0.6-0.7 mg resveratrol 1. From animal studies and limited human studies, it appears that resveratrol is absorbed from the gastrointestinal tract following its ingestion. However, the efficiency of its absorption, as well as its distribution, metabolism and excretion, are not well understood. Much research needs to be done in order to elucidate the pharmacokinetics of resveratrol in its various forms 1.