Grape seed extract is a rich bioflavonoid which is used for fighting free radicals and maintaining capillary health. It is very similar to pine bark extract, with a high content of proanthocyanidins. Free radicals do damage in the capillaries in two ways:
by inactivating a compound called 1-antitripsin, whose role is to restrain the enzymes that break down collagen, elastin, and hyaluronic acid; and
by turning the fats in the cell membranes rancid (lipid peroxidation).

Proanthocyanidins protect both the 1-antitripsin and the lipids by neutralizing the specific types of free radicals most likely to damage them, and may also directly inhibit the damaging enzymes. Collagen, elastin, and hyaluronic acid make up much of the inner wall and supporting matrix of the capillaries; when they are in good shape, the capillaries stretch to let red blood cells through the tight places and do not let the fluids in the blood leak out.

Proanthocyanidins have shown a marked tendency to accumulate in tissues with high contents of glycosaminoglycans (complex amino sugars), such as capillary walls and skin. This may also apply to cartilage and synovial fluid. Proanthocyanidins have also shown antimutagenic effects in vitro at high concentrations (250 mcg/ml). Proanthocyanidins (also known as leucoanthocyanidins and pycnogenols) are a form of polyphenol, which is in turn a form of bioflavonoid. Proanthocyanidins are at least 15 to 25 times more powerful than vitamin E in neutralizing the iron and reactive oxygen species / free radicals that attack lipids.
Grape seed extract is used for its free radical–fighting capabilities, and for a variety of conditions related to capillary health and permeability. It is synergistic with vitamin C, which is more potent and absorbed more rapidly when used together with proanthocyanidins.
Proanthocyanidins present in grape seeds are known to exert anti-inflammatory, antiarthritic, and antiallergic activities; to prevent skin aging; to scavenge oxygen free radicals; and to inhibit the damaging effects of UV radiation from sunlight. They also bond with collagen, the most abundant protein in the body and a key component of skin, gums, bones, teeth, hair, and body tissues.
Proanthocyanidins have been indicated for poor distribution of microcirculatory blood flow in the brain and heart; altered capillary fragility and permeability (in diabetes mellitus); chronic arterial/venous insufficiency in the extremities; altered platelet aggregation and other characteristics of blood flow in capillaries; breakdown in the elastic fibers of the capillaries (collagen and elastin) due to free-radical and enzyme action; microangiopathy of the retina, edema of the lymph nodes, varicose veins, and other symptoms of the problems listed above; the cumulative effects of aging; and reducing the risk of degenerative diseases.