Grape Seed Extract

Metadata

Approved Indications

Commission E (Germany)

• No Commission E monograph exists for grape seed extract
• Note: Commission E has a monograph for Vitis vinifera leaf (red vine leaf) for CVI, which is a different plant part with distinct composition

ESCOP

• No ESCOP monograph has been published for grape seed extract specifically

EMA/HMPC (European Medicines Agency)

• No EMA/HMPC monograph for grape seed (Vitis vinifera semen)
• Note: The EMA has published a monograph for Vitis vinifera L., folium (Red Vine Leaf) for CVI symptoms — this covers the leaf, not the seed, and involves different active constituents (primarily flavonoids in leaves vs OPCs in seeds)

Regulatory Context

• EU: Available as a food supplement; no classification as traditional herbal medicine for the seed extract
• US: Marketed as a dietary supplement; GRAS status; NCCIH has reviewed available evidence without making therapeutic recommendations
• France: Historically used in French phytotherapy for venous and microvascular indications (alongside pine bark)

Agreement/Disagreement Between Bodies

• Unanimous absence: No major European regulatory body has published a monograph for grape seed extract
• Distinction from Red Vine Leaf: It is important to distinguish grape seed extract (Vitis vinifera semen) from Red Vine Leaf (Vitis vinifera folium); the latter has EMA/HMPC and Commission E recognition for CVI
• NCCIH assessment: The US NCCIH notes that GSE has been studied for various conditions but that “the evidence for most uses is limited”

Conditions Treated

Primary (Moderate Evidence)

• Blood pressure reduction: Meta-analyses confirm modest but statistically significant DBP reduction (-2.2 mmHg) and heart rate reduction (-1.25 bpm); effects are most pronounced in younger adults, obese individuals, and those with metabolic syndrome
• Chronic venous insufficiency (CVI): Several studies support improvement in leg heaviness, swelling, and venous symptoms; evidence is less extensive than for horse chestnut or pine bark

Secondary (Limited Evidence)

• Endothelial function: RCT evidence shows improved flow-mediated dilation in some populations, particularly those with prehypertension
• Oxidative stress: Consistent antioxidant effects demonstrated across multiple studies; clinical significance for disease prevention is not established
• Peripheral edema: Reduction in postoperative edema and post-injury swelling in some studies

Traditional/Historical (Insufficient Clinical Evidence)

• Diabetic retinopathy and macular degeneration (based on antioxidant and microvascular rationale)
• Skin aging and UV protection (preclinical evidence is promising)
• Cancer prevention (in vitro and animal data only; no clinical trials supporting this use)
• Cognitive protection (preclinical only)
• Allergic conditions (limited pilot data)

Mechanism of Action

Primary Mechanisms

Endothelial function and nitric oxide production:

• OPCs enhance endothelial nitric oxide synthase (eNOS) expression through the AMPK/SIRT1/KLF2 signaling pathway
• Increased nitric oxide (NO) production leads to vasodilation and blood pressure reduction
• In vivo studies confirm that the antihypertensive effect is abolished when NO production is blocked, demonstrating NO as the critical mediator
• OPCs also reduce endothelin-1 (ET-1, a vasoconstrictor), shifting the vasodilator/vasoconstrictor balance

Antioxidant:

• OPCs are among the most potent natural antioxidants; ORAC values significantly exceed those of vitamins C and E
• Scavenge reactive oxygen species (ROS) and reactive nitrogen species (RNS)
• Upregulate endogenous antioxidant enzymes (SOD, catalase, glutathione peroxidase)
• Protect LDL cholesterol from oxidation (relevant to atherosclerosis prevention)

Vascular wall stabilization:

• OPCs bind to collagen and elastin fibers in vascular walls, increasing resistance to enzymatic degradation by elastase and collagenase
• Reduce capillary permeability and fragility
• This mechanism is shared with pine bark (Pycnogenol) and supports the CVI indication

Secondary Mechanisms

Bioavailability Notes

• Monomers (catechin, epicatechin) and small oligomers (dimers, trimers) are absorbed in the small intestine
• Larger polymeric proanthocyanidins are poorly absorbed but are metabolized by colonic microbiota into bioactive phenolic acid metabolites
• The degree of polymerization affects bioavailability: lower molecular weight fractions are more bioavailable

Clinical Evidence Summary

Volume of Evidence

• Moderate. Multiple meta-analyses have been published, drawing on a reasonable number of RCTs from diverse research groups. The evidence base is broader in authorship than pine bark (Pycnogenol) but individual studies remain small and short-term.

Key Studies

Blood Pressure

Chronic Venous Insufficiency

Evidence Gaps

• No large, long-term (>6 months) RCTs for any indication
• No Cochrane review dedicated to grape seed extract
• No head-to-head comparisons with horse chestnut (the gold standard for CVI) or pharmaceutical antihypertensives
• Inconsistent effects on systolic blood pressure (DBP effects more consistent than SBP)
• No standardized extract dominates the literature, making cross-study comparison difficult
• Limited data on cardiovascular hard endpoints (events, mortality)
• Dose-response relationship is non-linear and not fully characterized

European vs US/Anglophone Consensus

Safety Profile

Contraindications

• Known hypersensitivity to grapes or grape products
• Bleeding disorders (OPCs have mild antiplatelet activity)
• Pre-surgical: discontinue at least 2 weeks before elective surgery

Drug Interactions

• Anticoagulants/antiplatelets: OPCs may have mild antiplatelet activity; theoretical additive effect with warfarin, aspirin, clopidogrel. Clinical reports of significant interactions are lacking, but caution is warranted
• Antihypertensives: Potential additive blood pressure-lowering effect; monitor blood pressure
• CYP-450 enzyme interactions: In vitro data suggests potential modulation of CYP3A4, CYP2C9, and CYP2D6; clinical significance is unclear but caution is advised with narrow therapeutic index drugs metabolized by these enzymes
• Hypoglycemic agents: Possible additive effect on blood glucose; monitor in diabetic patients

Side Effects

• Generally well tolerated at doses up to 600 mg/day in clinical trials
• Mild and infrequent adverse effects: headache, nausea, dizziness, dry/itchy scalp
• No serious adverse events reported in clinical studies
• No hepatotoxicity or nephrotoxicity documented

Pregnancy/Lactation

• Pregnancy: Safety data in pregnancy is lacking; avoid in medicinal doses during pregnancy
• Lactation: Insufficient data; avoid during breastfeeding
• Children: Not specifically studied in children; not recommended without medical supervision

Clinical Dosage

Standard Dosage Forms

Key Dosing Notes

• Standardization: Look for products standardized to >=95% OPCs (oligomeric proanthocyanidins)
• Onset of action: Blood pressure effects may take 4-8 weeks to become apparent; CVI symptom improvement may begin within 2-4 weeks
• Duration: Most studies lasted 4-16 weeks; long-term data is limited but no safety signals have emerged
• Non-linear dose-response: Meta-analysis data suggests a non-linear dose-response relationship for blood pressure; more is not necessarily better
• Product variability: Different GSE products may vary in OPC composition (ratio of monomers to oligomers to polymers); standardization to total OPC content does not ensure identical compositions

Sources

• Terauchi M, et al. The effect of grape (Vitis vinifera) seed extract supplementation on flow-mediated dilation, blood pressure, and heart rate: a systematic review and meta-analysis of controlled trials with duration- and dose-response analysis. Pharmacol Res. 2021;174:105896
• Ras RT, et al. The effect of polyphenol-rich grape seed extract on blood pressure: a meta-analysis of randomized controlled trials. Nutr Res Rev. 2013;26(2):178-187
• Sivaprakasapillai B, et al. Effect of grape seed extract on blood pressure in subjects with the metabolic syndrome. Metabolism. 2009;58(12):1743-1746
• Park E, et al. Grape seed extract positively modulates blood pressure and perceived stress: a randomized, double-blind, placebo-controlled study in healthy volunteers. Nutrients. 2021;13(2):654
• Costantini A, et al. Clinical and capillaroscopic evaluation of chronic uncomplicated venous insufficiency with procyanidol oligomers (Leucoselect). Minerva Cardioangiol. 1999;47(1-2):39-46
• National Center for Complementary and Integrative Health (NCCIH). Grape Seed Extract fact sheet. nccih.nih.gov/health/grape-seed-extract
• Drugs.com. Grape Seed Uses, Benefits & Dosage. drugs.com/npp/grape-seed.html
• Edirisinghe I, et al. Grape seed proanthocyanidin extracts enhance endothelial nitric oxide synthase expression through 5’-AMP activated protein kinase/Sirtuin 1-Kruppel like factor 2 pathway. Biol Pharm Bull. 2012;35(12):2093-2101
• Sano A, et al. Procyanidin B1 is detected in human serum after intake of proanthocyanidin-rich grape seed extract. Biosci Biotechnol Biochem. 2003;67(5):1140-1143
• Ma ZF, Zhang H. Phytochemical constituents, health benefits, and industrial applications of grape seeds: a mini-review. Antioxidants. 2017;6(3):71

Connections

• Compare with Red Vine Leaf as a fellow Vitis vinifera product for venous health; Red Vine Leaf uses the leaf (flavonoid-rich) rather than the seed (OPC-rich) and has an EMA monograph for CVI
• Compare with Horse Chestnut as the best-evidenced herbal treatment for CVI; horse chestnut (aescin) has Cochrane-level evidence that grape seed extract lacks
• Related to Hawthorn as a fellow polyphenol-rich cardiovascular herb; hawthorn has Commission E and EMA approval for heart failure, while grape seed is positioned for blood pressure and venous health
• Related to Bilberry as another OPC/anthocyanidin-rich berry extract used for microvascular protection; both share the collagen-stabilizing and antioxidant mechanisms
• Compare with Green Tea as a fellow catechin-containing botanical with cardiovascular evidence; green tea catechins (especially EGCG) share structural similarity with GSE monomers but differ in polymerization pattern
• Mechanistically similar to Pine Bark (Pycnogenol) as both are rich in oligomeric proanthocyanidins; pine bark has more extensive clinical trial data but from a narrower research group