Today, grape seed extract is used as a folk or traditional remedy for conditions related to the heart and blood vessels, such as atherosclerosis (hardening of the arteries), high blood pressure, high cholesterol, and poor circulation …
[C]omplications related to diabetes, such as nerve and eye damage; vision problems, such as macular degeneration (which can cause blindness); swelling after an injury or surgery; cancer prevention; and wound healing.
"Studies have found that grape seed extracts may prevent the growth of breast, stomach, colon, prostate, and lung cancer cells in test tubes. However, there is no clear evidence whether it works in humans.
Antioxidants, such as those found in grape seed extract, may help reduce the risk of developing cancer. Grape seed extract may also help prevent damage to human liver cells caused by chemotherapy medications."
Grape seed extract also contains high levels of compounds (procyanidin dimers) that act as aromatase inhibitors. This is likely another way grape seeds may help prevent and treat cancer, specifically hormone-dependent breast cancer.
Aromatase, an enzyme, converts androgen to estrogen and is expressed at higher levels in breast cancer tissues than normal tissues.