“Grape seed contains pyrocyanidines, which are known to be potent antioxidants. In particular, they inhibit xanthine oxidase, an essential enzyme in the production of free radicals, as well as lipoperoxidase, an important potentiator of arterial plaque formation. No toxicity has been reported for grape seed extract. It should be taken in dosages of approximately 50 mg per day.” (p. 175)
Perls, T. and Silver, M. 1999. Living to 100. New York, N.Y.: Perseus Books Group.