The Benefits of Grape Seed Extract Supplements and Seeded Grapes

The equivalent of one and a quarter cup (295 ml) of fresh red, green, and blue-black grapes can improve artery function within three hours of consumption. Do that every day for a few weeks and artery function improves even further. They were even able to blunt the arterial dysfunction of a McDonald’s sausage and egg McMuffin meal.

The McMuffin mediation study included grapes with seeds, which harbor the bulk of the polyphenols in the fruit. Only 1 percent is found in the pulp and 5 percent in the juice. The grape skins hold 30 percent of the polyphenols, but the seeds hold the remaining 64 percent. Unfortunately, it’s hard to find seeded grapes. What about just taking grape seed extract supplements?

To see if grape seed extracts could prevent DNA damage, researchers drew blood from people in the hours following a grape seed supplement. The scientists then blasted their blood cells with radiation equivalent to 15,000 chest x-rays. Compared to the irradiated blood of those who didn’t take a supplement, within two hours the DNA damage seen in the grape seed group’s blood was as much as halved. This may help explain why those taking grape seed extract supplements appeared to be less likely to develop a type of skin cancer (squamous cell carcinoma) in an observational study. Interventionally, it can decrease markers of inflammation but what, if anything, has it been shown to do clinically? The only such study I could find was a small pilot study of nonalcoholic fatty liver disease patients, in which three months of grape seed extract supplementation significantly reduced liver fat and inflammation. But without a control group we can’t be sure they wouldn’t have gotten better without the treatment.

Powdered whole grape seeds do extend the healthspan and lifespans of rats, but the reason I recommend getting grape seeds from grapes rather than extracted into supplements is that there have been reports of adverse effects. One study found that grape seed extracts combined with vitamin C increased blood pressures in hypertensive individuals. And there was a case report of recurrent nausea, vomiting, diarrhea, and severe weakness attributed to such a supplement. The symptoms resolved after he stopped taking the grape seed extract supplement and then re-emerged when he resumed it. The researchers suggested it might be due to contamination with the toxic preservatives, benzethonium chloride and triclosan.

I’ve found the best odds of finding seeded grapes are at Asian markets, where you might be lucky enough to find Kyoho grapes (from the Japanese Kyoho budo, meaning “giant mountain grape”), dark purple globes with tasty large oval seeds. Fresh grapes are wonderful, but be careful if you have small children around. Whole grapes are among the most dangerous foods in terms of choking risk because they are just larger than a young child’s airway, yet smooth and deformable, so can become firmly wedged in place. Until their sixth birthday, grapes should be cut lengthwise for kids, or preferably even into quarters.