Also known as: GSE, OPC, Oligomeric proanthocyanidins, Vitis vinifera, Grape polyphenols
BotanicalGood evidence
A polyphenol-rich extract from the seeds left over from winemaking, standardised to proanthocyanidins. Best supported for vascular measures, and one of the better-evidenced antioxidant botanicals.
Typical dose
150.0–300.0 mg per day
With food, split across the day
What it is
Grape seed extract is made from the seeds of Vitis vinifera, largely a by-product of the wine industry. The seeds are notably rich in polyphenols despite being discarded in winemaking.
The compounds of interest are proanthocyanidins, often called OPCs, which are chains of flavanol units. Extracts are standardised to proanthocyanidin content, commonly 95 per cent.
Chain length matters for absorption. Shorter chains, particularly monomers and dimers, are absorbed reasonably well, while longer chains largely are not and instead act in the gut or are broken down by gut bacteria into smaller metabolites. This is why a headline proanthocyanidin percentage tells you less than it appears to.
How it works
Proanthocyanidins have strong antioxidant activity, but the more relevant mechanism in humans appears to be their effect on blood vessels. They support nitric oxide availability and endothelial function, which improves how readily vessels widen.
They also inhibit enzymes that break down collagen and elastin in vessel walls and connective tissue, which underpins the traditional use for vascular and skin integrity.
There is additional research on effects on inflammatory signalling and on the gut microbiota, since the poorly absorbed longer chains reach the colon intact and are metabolised there.
What the evidence shows
Blood pressure is the best-supported outcome. Meta-analyses have reported small but consistent reductions, more evident in people with elevated readings and in younger or overweight participants than in the already healthy.
Vascular function measures have shown reasonably consistent improvement, which fits the proposed mechanism and is the most coherent part of the evidence base.
There is a smaller literature on leg swelling and circulation, and on skin outcomes, with modest findings. Antioxidant capacity measures reliably improve, though as always that is a laboratory measure rather than a health outcome. Overall this is a decent, unglamorous ingredient with real if modest support.
Dosing
Typical range is 150-300 mg daily of standardised extract, often split across two servings. Trials on blood pressure have generally used doses in this band over 8-16 weeks.
Take with food. Polyphenol absorption is generally improved by a meal, and it reduces the chance of stomach upset.
Effects on vascular measures accrue over weeks rather than acutely. It combines sensibly with other vascular ingredients such as citrulline or beetroot, since the mechanisms are complementary rather than duplicative — one supports nitric oxide production, the other supports the vessel's capacity to respond.
Absorbed fractions clear within hours; vascular effects accrue over weeks
Timing
With food, split across the day
Competition status
Permitted — not on the WADA Prohibited List
Category
Botanical
Safety and side effects
Grape seed extract is well tolerated. Reported effects are mild and infrequent, mainly headache, digestive upset and nausea.
It has a mild effect on how readily blood clots and may lower blood pressure, so take care if either is being managed and stop before scheduled surgery.
Speak to your doctor before use if you take regular medication. People sensitive to grapes should avoid it.
Who should avoid it
Take care if your blood pressure is being managed or if you take anything affecting blood clotting. Stop before scheduled surgery. Speak to your doctor before use if you take regular medication. Avoid if sensitive to grapes. Not established at supplemental doses in pregnancy or breastfeeding.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
