Grape seed extracts are industrial derivatives from whole grape seeds that have a great concentration of vitamin E, flavonoids, linoleic acid and phenolic procyanidins (also known as OPC or oligomeric procyanidins). The typical commercial opportunity of extracting grape seed constituents has been for chemicals known as polyphenols having antioxidant activity in vitro.
According to the American Cancer Society, "there is very little reliable scientific evidence available at this time that drinking red wine, eating grapes, or following the grape diet can prevent or treat cancer in people".
One clinical trial with adults having coronary disease or cardiac risk factors concluded that: "Four weeks of muscadine grape seed supplementation in subjects with increased cardiovascular risk did not produce a statistically significant increase in brachial flow-mediated vasodilation or a significant change in other biomarkers of inflammation, lipid peroxidation, or antioxidant capacity. However, the muscadine grape seed supplement did result in a significant increase in resting brachial diameter. The clinical significance of the effect on resting diameter is not yet established."
A meta-analysis of randomized controlled trials concluded that "grape seed extract appears to significantly lower systolic blood pressure and heart rate, with no effect on lipid or C-reactive protein levels."
The US National Center for Complementary and Alternative Medicine reported that oral administration of grape seed extract was well tolerated in people over 8 weeks. In one completed clinical trial, grape seed extract did not alleviate the hardening of breast tissue in female patients undergoing radiation therapy to treat breast cancer.
Dosage, precautions and interactions
Oral grape seed extract is used in capsules or tablets usually containing 50 mg or 100 mg. Insufficient scientific information is known, however, about how long-term use of grape seed extract might affect health or any disease.
Side-effects and cautions, other NCCAM advisories.
In general, grape seed extract is well tolerated when taken by mouth, although it is better tolerated when encapsulated, as its taste is bitter. It has been used safely for up to 8 weeks in clinical trials.
^Feringa, Harm H.H.; Laskey, Dayne A.; Dickson, Justine E.; Coleman, Craig I. (2011). "The Effect of Grape Seed Extract on Cardiovascular Risk Markers: A Meta-Analysis of Randomized Controlled Trials". Journal of the American Dietetic Association111 (8): 1173–81. doi:10.1016/j.jada.2011.05.015. PMID21802563.
^Kijima, I.; Phung, S; Hur, G; Kwok, SL; Chen, S (2006). "Grape Seed Extract is an Aromatase Inhibitor and a Suppressor of Aromatase Expression". Cancer Research66 (11): 5960–7. doi:10.1158/0008-5472.CAN-06-0053. PMID16740737.