Oligomeric Procyanidins (OPCs), also called Proanthocyanidins, are a class of nutrients belonging to the flavonoid family. OPCs is often used interchangably with PCOs (procyanidolic oligomers) as well. OPCs have strong antioxidant abilities. They also play a role in the stabilization of collagen and the maintenance of elastin - both proteins in the connective tissue that support organs, joints, blood vessels, and muscle. OPCs have also been used to support vision and for anti-inflammatory activities. OPCs can be found in many plant sources, although the richest are pine bark, grape seed, and grape skin. Other notable sources are bilberry, cranberry, black currant, and green tea.