Proanthocyanidins: Biological activities associated with human health

Proanthocyanidins, also called condensed tannins, are oligomers and polymers of monomeric flavans linked through specific single (B linkages) and double (A linkages) bonds. These secondary plant metabolites have substantial antioxidant activity. They are prevalent in some foods and dietary supplements including several berries, red grapes and their wines, and seeds, baking chocolate, cinnamon, pycnogenol, and Ginkgo biloba. Calculations based on limited food composition data suggest daily intakes of about 54 mg/day per person in the United States. Similar data are unavailable to estimate intakes from dietary supplements. Studies on digestion of proanthocyanidins indicates only monomers and dimers are absorbed; however, preliminary evidence suggests hydroxylated phenolic acids are important products of gastrointestinal microflora activity that also may be absorbed. Several types of investigations support improved vascular health after short- or long-term consumption of proanthocyanidins or foods and supplements that contain them. These effects include vasodilation, presumably as a result of increased NO production, decreased platelet aggregation, reduced sensitivity of low-density lipoproteins (LDL) to oxidization, and modulation of several reactions associated with inflammation. Studies with cranberries and cinnamon, both of which contain uniquely linked proanthocyanidins, support a role for bacterial antiadhesion and improved glucose metabolism in type 2 diabetics, respectively. Results from a variety of experiments indicate proanthocyanidins may modulate several reactions involved in cancer processes. A crucial research need is to identify further biologically active components of proanthocyanidins so that mechanisms of action at the tissue, cellular, and subcellular levels