A new study has reported that grape seed proanthocyanidins can prevent precancerous changes in human breast cancer cells that are normally induced by repeated applications of low-dose carcinogens. In the study, the activity of grape seed proanthocyanidin extract in suppressing cellular carcinogenesis induced by repeated exposures to low doses of a combination of two carcinogens was studied. This treatment would normally be expected to induce cancer-related cellular changes. The authors identified several mechanisms of action by which grape seed proanthocyanidins suppressed such changes. The authors conclude that grape seed proanthocyanidins are candidates for the prevention of human breast cancer associated with long-term exposure to environmental carcinogens.

Proanthocyanidins are found in various healthy foods

This study confirms the findings of previous studies that have reported a chemopreventive role for grape seed components (resveratrol, which is not a proanthocyanidin, is the best known). The following foods are good sources of proanthocyanidins (which are dimers or oligomers of catechin and epicatechin and their gallic acid esters) some of these foods been found to be associated with reduced risk of breast cancer in numerous studies:

Green tea

Pistachio nuts

Note that while the study used a grape seed extract, grape skins are also a good source of proanthocyanidins. We do not recommend taking grape seed extract for purposes of preventing or treating breast cancer primarily because safe and effective levels of such supplementation have not been established. Antioxidants such as beta-carotene and vitamin C, which have been found to be associated with lower risk of cancer when consumed as part of food, have been found to promote cancer growth when taken in concentrated form. Grape seed extract and resveratrol require more study to ensure that the same sort of unintended adverse effect does not result from supplementation. In fact, one study found that the degree of mammary cancer chemoprevention by grape seed extract in rats depended on the diets fed to the rats. Another study found that grape seed extract has weak estrogenic activity. We urge those with breast cancer or at high risk for it to obtain the benefits of proanthocyanidins by consuming food.