Grape Seed Extract

Grape seed extract is an industrial preparation made from the seeds of the common grape, Vitis vinifera, a byproduct of the wine and grape-juice industries. Its principal constituents are proanthocyanidins, polymeric flavonoids built from catechin and epicatechin units and often referred to as oligomeric proanthocyanidins; high-quality extracts consist largely of these procyanidin compounds, which impart an astringent taste and pronounced antioxidant properties in the test tube ^[3]. The extract also contains other flavonoids and phenolic acids.

The seeds are dried and the polyphenols drawn out with water or organic solvents, and the resulting extract is standardized by its proanthocyanidin content, commonly assessed by chromatographic methods. Grape seed extract is sold as a dietary supplement in capsules, tablets, and liquid forms, and it is marketed broadly for antioxidant and cardiovascular support, for circulation, and for skin health. It is one of several grape-derived polyphenol products, alongside extracts of grape skin and whole grape.

Human research has focused on cardiovascular and metabolic outcomes. A meta-analysis of randomized trials found that grape seed extract produced statistically significant reductions in systolic and diastolic blood pressure, with larger effects in younger or obese participants and in those with metabolic syndrome ^[1]. Another systematic review and meta-analysis reported modest improvements in fasting blood glucose and in total, low-density lipoprotein cholesterol, and triglycerides, along with a marker of inflammation, though it found no clear effect on body weight or long-term glucose control ^[2]. Laboratory and animal studies describe antioxidant, anti-inflammatory, and photoprotective effects of grape seed proanthocyanidins, including protection against ultraviolet-induced skin damage ^[3]. Overall, individual trials tend to be small, and the clinical significance of the findings is still debated.

Grape seed extract is regulated as a dietary supplement rather than an approved drug, and it is not authorized to treat or prevent disease; notably, it has been falsely promoted as a cancer cure, a claim without clinical support. Human trials indicate that it is generally well tolerated, with side effects such as itchy scalp, dizziness, headache, or nausea reported occasionally ^[2]. As with other polyphenol supplements, people taking anticoagulant medications or with bleeding concerns are sometimes advised to use caution, and standardized products vary in their exact composition.

Very well tolerated for most people. Occasional mild side effects include headache, nausea, or upset stomach. Because it can have a mild blood-thinning and blood-pressure-lowering effect, be cautious if you're on anticoagulants or antihypertensives.