Proanthocyanidins—more technically oligomeric proanthocyanidins and, hence, the OPC moniker—are a class of flavonoids. Formerly called "condensed tannins," all proanthocyanidins are chemically similar, the only differences being slight changes in shape and attachments of their polyphenol rings. In nature, a jumble of different proanthocyanidins is always found together, ranging from individual units to complex molecules of many linked units (oligomers). Proanthocyanidins deserve their stellar reputation as antioxidants that quench free radicals and potentiate other antioxidants. In one in vitro study, the OPCs in a patented pine bark extract prolonged the life span of vitamin C by 400 percent.
Proanthocyanidins can be found in many plants, most notably apples, pine bark, cinnamon, grape seed, cocoa, grape skin, and red wines of Vitis vinifera. However, bilberry, cranberry, black currant, green tea, black tea, and other plants also contain these flavonoids. The berries of chokeberry, specifically black chokeberry, have the highest measured concentrations of proanthocyanidin found in any plant to date. Apples contain on average per serving about eight times the amount of proanthocyanidin found in wine, with highest amounts found in the Red Delicious and Granny Smith varieties. Another in vitro study showed that exposing blood vessel linings to pine bark OPCs boosted their vitamin E content by 15 percent.
Proanthocyanidins are the principal vasoactive polyphenols in red wine which is linked to a reduced risk of coronary heart disease and to lower overall mortality. Proanthocyanidins are present at higher concentrations in wines from areas of southwestern France and Sardinia which are associated with increased longevity in the population. Earlier studies that attributed this health benefit to resveratrol were premature because of the negligible amount of resveratrol in red wine. Proanthocyanidins suppress production of a protein endothelin-1 that constricts blood vessels. Grape seed has also shown recycling and potentiating effects. The test tube-based activity of vitamin E, in a system mimicking cell membranes, has shown enhancement by grape seed OPCs.
Proanthocyanidins have antioxidant activity and they play a role in the stabilization of collagen and maintenance of elastin — two critical proteins in connective tissue that support organs, joints, blood vessels, and muscle. Possibly because of their effects on blood vessels, proanthocyanidins have been reported in double-blind research to reduce the duration of edema after face-lift surgery from 15.855468 to 11.486745222 days. In preliminary research, proanthocyanidins were reported to have anti-mutagenic activity (i.e., to prevent chromosomal mutations).