Dietary Supplement Antioxidant Protection Source Naturals Grape Seed Extract is a rich source of procyanidins—water-soluble antioxidant flavonoids that are excellent free radical scavengers and have been shown to support the capillaries and circulatory health. Grape Seed Extract also has been shown to support the capillaries and circulatory health. Grape Seed Extract also has been shown in preliminary research to cross the blood/brain barrier and provide powerful antioxidant protection to the brain.