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Grape (Vitis vinifera L.): A Comprehensive Reference

1. Identity: Botanical Classification, Chemical Names, and Natural Source

Botanical name: Vitis vinifera L. (synonym: Vitis vinifera subsp. vinifera). The NCBI Taxonomy system classifies Vitis vinifera as a species within the family Vitaceae, order Vitales, within the eudicotyledon clade of flowering plants. Common names include wine grape, European grape, and vine grape. The extract derived from seeds is marketed under several common names, including grape seed, grape seed extract, Muskat, oligomeric proanthocyanidin complexes (OPC), proanthocyanidin, and procyanidolic oligomers (PCO).

Grapevine (Vitis vinifera L.) represents one of the most cultivated fruit crops on a global scale, with a production reaching approximately 75 million tons of berries overlaying approximately 7.5 million hectares. The main cultivation regions of V. vinifera are located in Europe (France, Italy, and Spain), Asia (China), and the Americas (United States, Argentina, and Chile).

Vitis vinifera is diploid with 2n = 38 chromosomes, a fixed number shared across the genus Vitis.

Parts used as dietary supplements or functional ingredients: Different extracts are obtained from the plant from various organs, including the fruit, skin, pomace, seed, leaf, and stem. Grape marc — a mixture of grape seeds and skins — remains as a by-product of the wine production process, making up 20–25% of the grape's weight. Grape seeds contain fats, proteins, carbohydrates, and 5–8% polyphenols. The grape seed is rich in extractable phenolic antioxidants such as phenolic acids, flavonoids, proanthocyanidins, and resveratrol, and the grape skin is abundant in anthocyanins.

Common commercial preparations include:

• Grape seed extract is usually available in liquid extracts, tablets, or capsules; its main active ingredient is oligomeric proanthocyanidin complexes (OPCs), though some formulations may have varying amounts.
• Resveratrol (isolated from grape skin) is available without prescription as a nutritional supplement in multiple preparations and doses.
• Whole grape juice and concentrated grape juice polyphenol products.
• Grape seed oil (cold-pressed), though cold-pressed grape seed oil contains little proanthocyanidin content because of its insolubility in lipids, and no resveratrol, which is found primarily in grape skin.
• Dried whole grape (raisins) and grape pomace powders.

2. Traditional and Historical Use

Prehistoric and Ancient Origins

Grapes have been consumed since prehistoric times and were one of the earliest domesticated fruit crops. According to archaeological evidence, domestication had occurred by approximately 8000 BCE in the Transcaucasia area (which encompasses present-day Armenia, Azerbaijan, and Georgia and parts of both Iran and Turkey) and spread south to present-day Syria, Iraq, Jordan, and Egypt before moving toward Europe, where viticulture had been established in Spain by approximately 1000–800 BCE and France by ca. 600 BCE. Wine production followed soon after grape domestication, and the earliest known evidence of winemaking was discovered in the Republic of Georgia and dates to roughly 8000 BCE.

Ancient Egypt

The Ebers Papyrus, an Egyptian medical document that dates to 1500 BCE, called for the use of medicated wines for a variety of conditions, including digestive issues and jaundice. Chemical analyses of ancient organics absorbed into pottery jars from the beginning of advanced ancient Egyptian culture, ca. 3150 BCE, and continuing for millennia revealed that a range of natural products — specifically, herbs and tree resins — were dispensed by grape wine.

Ancient Greece and Rome

The medicinal use of grapes was especially advanced in ancient Greece, where Hippocrates, the "father of medicine," incorporated them into treatments for a wide array of conditions, from fevers to sepsis. The Romans further developed the use of grapes in medicine, using them to treat digestive issues and as a form of nourishment for the sick.

Traditional Chinese Medicine

In traditional Chinese medicine (TCM), grapes are considered to have cooling properties and are used to treat conditions associated with heat, such as fever and inflammation. Chinese traditions made use of medicated wines, with ancient recipes dating to the Shang Dynasty.

Native American Traditions

In North America, Native American tribes such as the Cherokee and Seminole turned to the grape, particularly Vitis aestivalis (Norton wine grape). They used it to treat gastrointestinal issues, fevers, body aches, and even as a remedy for chronically ill babies. The Cherokee referred to the grape as "telû΄latĭ," and it became a staple in their traditional medicinal practices.

Summary of Traditional Preparations and Purposes

Wine often has been used as a medium for producing herbal remedies, due to the solvent nature of the alcohol. Traditional applications across cultures spanned nutritional support during illness, fever reduction, treatment of gastrointestinal complaints, topical wound care, and general vitalization. It bears emphasis that these historical uses preceded modern scientific investigation and reflect ethnobotanical, not evidence-based clinical, practice.

3. Key Constituents and Active Compounds

The biological activity of V. vinifera is determined by the presence of high contents of polyphenols, mainly flavonoids (e.g., quercetin, kaempferol), catechin derivatives, anthocyanins, and stilbenoids (e.g., trans-resveratrol, trans-ε-viniferin). It is a rich source of secondary metabolites, particularly flavonoids (flavan-3-ols, flavonols), phenolic acids, anthocyanins, fatty acids, amino acids, and vitamins.

Grape seeds contain vitamin E; polyphenols including gallic acid, catechins, proanthocyanidins, resveratrol, and tannins; polyunsaturated fatty acids including linoleic, oleic, and alpha-linolenic acids; protein; and carbohydrates. Total proanthocyanidin content consumed in 100 g of dried grape seed is approximately 3,500 mg, although composition of commercial preparations is highly variable.

The major bioactive compound classes and their characteristics are:

Proanthocyanidins (Oligomeric Proanthocyanidins / OPCs)

Grape seed proanthocyanidins (GSPs) contain dimers, trimers, and oligomers of catechin and epicatechin, and have been reported to resist oxidative stress and to promote DNA repair. Proanthocyanidins are water-soluble and can cross the blood-brain barrier more easily than other natural antioxidants, such as quercetin and curcumin. These are the primary active compounds in grape seed extract.

Resveratrol

Resveratrol is a biologically active and well-characterized constituent of grape, present in abundance in the flesh of the fruit and known for its various medicinal properties. A large amount of resveratrol is produced in the skin of grapes to protect the plant against fungal diseases and sun damage; therefore, wine has higher levels of resveratrol compared to other natural foods. The purity of commercial resveratrol products is rarely well defined, its oral bioavailability is poor, and the component responsible for its activity is not fully known. Resveratrol exists in both trans and cis configurations, and the major form found in plasma is a sulfated or glucuronidal conjugate rather than free resveratrol.

Anthocyanins

Grape skins — especially those from red and black cultivars — are particularly rich in anthocyanins, which give the fruit its characteristic color and contribute to antioxidant activity. The main V. vinifera groups of compounds are phenolic constituents and aromatic acids; stilbenoid compounds have also been identified in relatively large amounts.

Flavonols and Flavanols

Quercetin inhibits the oxidation of LDL and cholesterol and the clumping of platelets. Kaempferol is also documented among the flavonol constituents of grape tissue. Catechin and epicatechin are the predominant flavanols.

4. Established and Proposed Mechanisms of Action

Antioxidant Activity

The most cited bioactive property attributed to the phenolic compounds is their antioxidative capacity, preventing the oxidation of LDL lipoproteins, platelet aggregation, and the damage of red blood cells through radical scavenging. Removal of free radicals (mainly hydroxyl radicals) and chelation of metals are the biological mechanisms associated with the antioxidant property, influencing functioning of the immune system and cell signaling. The radical scavenging activities of phenolic compounds are supported by their reducing power through hydrogen donating and single oxygen quenching.

Anti-inflammatory Mechanisms

Chronic inflammation is a main mediator in the development of chronic diseases such as cancer, Alzheimer's, neurodegenerative diseases, cardiovascular diseases, diabetes, arthritis, and pulmonary diseases. When signal-dependent transcription factors such as NF-κB and activating protein 1 (AP-1) are activated, they induce the expression of genes involved in the inflammatory response. Intensive production and secretion of pro-inflammatory cytokines and chemokines can amplify the initial inflammatory response. Grape polyphenols, including resveratrol and proanthocyanidins, have been shown to modulate NF-κB and related inflammatory pathways in preclinical models.

Vascular and Nitric Oxide Mechanisms

Grape seed extract works by neutralizing free radicals, reducing inflammation, and improving blood vessel function through enhanced nitric oxide production. Quercetin inhibits the oxidation of LDL and cholesterol and the clumping of platelets. Other beneficial effects are exerted by resveratrol, epicatechin, epigallocatechin gallate (EGCG), epicatechin gallate (ECG), genistein, and daidzein — namely, they protect against atherosclerosis and alleviate arrhythmias of the heart.

Antiplatelet and Anticoagulant Activity

Research analysis of grape seed extract demonstrated effects on coagulation times, thromboelastometry, and platelet aggregation. ADP-induced aggregation was lower with GSE.

SIRT1/AMPK Pathway Activation

Studies revealed that resveratrol may promote intracellular amyloid-beta (Aβ) clearance, in part by activating autophagy and AMPK signaling in vivo. Resveratrol can act on adipocytes, increasing the expression of browning-related genes in white adipose tissue through the SIRT1/AMPK pathway, thereby reducing fat accumulation.

Anticancer Mechanisms (Preclinical)

Stilbenes including resveratrol and their precursors appear to be of preventative and possibly therapeutic value in atherosclerosis and certain neoplastic and inflammatory afflictions. The probable mechanisms are free radical scavenging and selective interference with a multitude of factors affecting the division cycle of rapidly and abnormally proliferating mammalian cells. Resveratrol (~25 micromolar) potentiated grape seed extract (≤ 35 µg/mL) induced colon cancer cell apoptosis via activation of p53-dependent pathways, with elevation of apoptosis much more pronounced in p53+/+ cells compared to p53−/− cells. Apoptosis was strongly correlated with pp53 levels and Bax:Bcl-2 ratio, key players in the mitochondrial apoptotic pathway. These findings are from in vitro and animal studies and have not been confirmed in human clinical trials for cancer treatment.

5. Scientific Evidence by Area of Use

5.1 Cardiovascular Health — Blood Pressure

This is the area with the most robust human clinical evidence for grape-derived preparations.

Nine randomized, controlled trials (N=390) met the inclusion criteria for a meta-analysis; grape seed extract significantly lowered systolic blood pressure (weighted mean difference −1.54 mm Hg, 95% confidence interval −2.85 to −0.22, P=0.02) and heart rate (WMD −1.42 bpm, P=0.01). No significant effect on diastolic blood pressure, lipid levels, or CRP was found.

A subsequent and larger meta-analysis confirmed and extended these findings: twelve articles involving 16 clinical trials and 810 study subjects were analyzed, with overall analyses finding significant reductions for SBP (WMD = −6.077 mmHg; 95% CI: −10.736 to −1.419; P = 0.011) and DBP (WMD = −2.803; 95% CI: −4.417 to −1.189; P = 0.001) after grape seed extract treatment. The findings demonstrated that grape seed extract exerted a beneficial impact on blood pressure, and this impact was more obvious in younger or obese subjects, as well as in patients with metabolic disorders. However, the heterogeneity between these trials (I² = 94.0% for SBP) was high, limiting confidence in the pooled estimates.

A further systematic review and meta-analysis identified 30 eligible RCTs: pooled results indicated that compared to the control group, consumption of grape products significantly decreased systolic blood pressure (SBP) (WMD = −3.17 mmHg; 95% CI: −5.36, −0.99 mmHg; P = 0.004). The certainty of evidence from RCTs was characterized as low, with grape products in whole forms showing a small reduction in SBP but not clearly influencing other markers of cardiovascular health.

Evidence strength: Moderate-to-low. Multiple meta-analyses of RCTs show a statistically significant but modest reduction in SBP and sometimes DBP. High heterogeneity across trials and low certainty of evidence ratings limit definitive conclusions.

5.2 Cardiovascular Health — Lipids and Atherosclerosis

Observational studies indicate that the intake of polyphenol-rich foods improves vascular health, thereby significantly reducing the risk of hypertension and cardiovascular disease (CVD). However, data from controlled intervention trials on lipid lowering are less consistent. One meta-analysis found no significant effect of grape seed extract on diastolic blood pressure, lipid levels, or CRP. Some individual studies report modest LDL reductions, but these are not uniformly confirmed.

Evidence strength: Weak-to-moderate for observational associations with cardiovascular risk; lipid-lowering effects remain inconsistent in RCTs.

5.3 Oxidative Stress Biomarkers

A systematic review and meta-analysis of RCTs examined grape products containing polyphenols on antioxidant markers: subgroup analysis found that intake of grape polyphenol-containing products had a significant effect on total antioxidant capacity in healthy individuals (WMD = 0.524 µmol/L; 95% CI: 0.42, 0.62; P < 0.001), but not in participants with abnormal weight. Effects on specific antioxidant enzymes (SOD, ORAC) were not consistently significant across available RCTs.

Evidence strength: Preliminary to moderate. Improvements in total antioxidant capacity are seen in some subgroups; effects on specific oxidative stress biomarkers are mixed.

5.4 Diabetes and Glycemic Control

Evidence has been found suggesting that dietary polyphenols and polyphenol-rich foods are beneficial for preventing and managing diabetes. Several reviews have illustrated that natural polyphenols are potential multifunctional agents to reduce the risk of diabetes and diabetic complications. Grape polyphenols exert antiglycative and antioxidant effects which may contribute to preventing chronic diseases; however, clinical evidence of grape polyphenols on chronic disease prevention and treatment by glycation markers modulation is limited.

Some small RCTs report modest reductions in HbA1c and fasting glucose with GSE, but study quality is generally low to moderate and sample sizes are small. Intake of 2 g/d grape polyphenol in overweight and obese participants with type 2 diabetes and 0.5 g/d resveratrol supplementation had no significant effect on some glycemic markers in certain trials.

Evidence strength: Weak-to-preliminary. Small, heterogeneous trials yield inconsistent results; no confirmed clinical benefit for glycemic management has been established.

5.5 Cognitive Function and Neuroprotection

Preclinical work in rodents provides mechanistic background: one study evaluated the benefits of grape seed proanthocyanidin extract (GSPE) in treating the effects of age-related oxidative stress and accumulation of lipofuscin on cognitive ability in rats. Female Wistar rats at 3 and 12 months of age received a daily oral supplement of GSPE. Blood glucose and markers of oxidative stress were assessed in the hippocampus; GSPE lowered blood glucose, lipid peroxidation, and hydrogen peroxide level, and increased protein sulphydryl content in the hippocampus. In addition, GSPE significantly improved cognitive performance in both age groups.

In humans, a community-based, randomized, double-blind, placebo-controlled trial was conducted hypothesizing that grape seed procyanidins extract (GSPE) would have a favorable effect on cognitive function in elderly people with mild cognitive impairment (MCI). Participants aged 60 years or older with MCI were randomly assigned into the GSPE group (n = 35, 320 mg/d) or placebo group (n = 36) and received capsules for 6 months. Cognitive function was assessed using the Montreal Cognitive Assessment Scale (MoCA).

Regarding Alzheimer's disease mechanisms, quercetin-3-O-glucuronide from red wines and Concord grape juice is capable of reaching the brain and contributes to protection against Alzheimer's disease by modulating multiple mechanisms, including reducing Aβ generation, reducing Aβ oligomerization, and promoting neuroplasticity processes — though this was demonstrated in preclinical models.

Evidence strength: Primarily preclinical (animal/in vitro). A small number of human RCTs exist, but they are limited in size and scope. Human evidence for meaningful cognitive benefit remains preliminary.

5.6 Cancer — Chemopreventive Research

Research into grape-derived polyphenols and cancer is largely preclinical. Grape seed extract (GSE) and resveratrol (RSV) are potent chemopreventive agents against colon cancer both in vitro and in vivo, at relatively high concentrations. Resveratrol is reported to strongly exhibit chemo-preventive and antineoplastic activity in laboratory settings.

An important safety caveat exists: evidence exists for a dual cancer-promoting or inhibitory role for resveratrol in breast cancer, dependent on estrogenic or antiestrogenic activities. Moreover, much of the inhibitory effects of resveratrol have been reported from studies with high, non-physiological concentrations. Findings from one animal study implicate low concentrations of resveratrol in potential promotion of breast cancer, illuminating the importance of further delineating resveratrol's concentration-dependent effects, particularly in breast cancer, before it can be tested in the clinic or used as a dietary supplement for breast cancer patients.

Evidence strength: Weak and preliminary for humans. Cancer-related effects are demonstrated in cell culture and animal models; no human clinical trials have established grape-derived supplements as effective cancer treatments or preventatives. The dual promoting/inhibiting data in breast cancer models calls for caution.

5.7 Gastrointestinal Health

GSE rich in proanthocyanidin protects and provides immunity against chronic and acute gastric and intestinal oxidative injury through membrane microviscosity in gastric and duodenal membrane and inhibition of lipid peroxidation. Resveratrol is a polyphenol found in GSE that suppresses the growth of Helicobacter pylori, IL-8 secretion induced by H. pylori, generation of reactive oxygen species, and changes in human gastric epithelial cells morphology. These findings are primarily from preclinical or in vitro models.

5.8 Skin Health

The grape seed extract (GSE) and its main active polyphenol, resveratrol (RES), have shown considerable antioxidant activities, besides possessing protective and therapeutic effects against various skin complications. Preclinical data and limited clinical pilot studies support topical and oral applications for photoprotection and wound healing, but large human trials are lacking.

6. Body Systems and Health Areas of Association

Research has covered the medical effects of grape-derived compounds on cancer, cardiovascular disease, brain and neurological disorders, eye diseases, skin disorders, kidney health, diabetes, and gastric diseases, along with medical applications in drug delivery, wound dressing, and tissue engineering.

• Cardiovascular system: Blood pressure regulation, endothelial function, lipid oxidation, platelet aggregation, and atherosclerosis.
• Central nervous system: Neuroprotection, amyloid-beta modulation, age-related cognitive decline.
• Metabolic/endocrine: Glycemic control, insulin sensitivity, adipose tissue metabolism.
• Gastrointestinal tract: Gastroprotection, gut microbiome modulation, H. pylori inhibition.
• Integumentary system: Photoprotection, wound healing, anti-aging via collagen support.
• Musculoskeletal: GSE is a rich source of proanthocyanidin, which strengthens the collagen-based tissues by increasing collagen cross-links, and also increases the synthesis of collagen and the conversion of collagen from soluble to insoluble form.
• Immune system: Anti-inflammatory modulation via NF-κB and cytokine pathways.

7. Dosage Forms and Dosages Reported in Studies

In clinical trials, grape seed extract has been studied for effects on various cardiovascular risk markers at oral doses of 150 to 2,000 mg/day; formulations and durations of therapy (range, 2 to 24 weeks) varied.

In human trials, doses of resveratrol have ranged from 20 mg to 5 gm daily, but a typical over-the-counter recommended dose is 500 mg twice daily.

In one randomized, double-blind, placebo-controlled trial, participants with mild cognitive impairment received grape seed procyanidins extract at 320 mg/d for 6 months.

Grape seed extract appears to be generally well tolerated at dosages up to 2,500 mg per day.

Composition of commercial grape seed preparations is highly variable. This variability in OPC content, standardization, and extraction method means that dose comparisons across products are difficult.

8. Safety Considerations and Drug Interactions

General Tolerability

Clinical trials have generally reported that grape seed extract is well tolerated. At present, there is no conclusive evidence that resveratrol has beneficial effects in humans; on the other hand, it has few if any side effects. Side effects may include minor gastrointestinal upset, nausea, headache, and fatigue, and possible supplement-drug interactions with estrogens and anticoagulants.

Anticoagulant and Antiplatelet Interactions

GSE has antiplatelet properties and may interact with anticoagulants (warfarin, DOACs) and antiplatelet drugs, increasing bleeding risk. Herbs with anticoagulant/antiplatelet properties may enhance the adverse/toxic effect of thrombolytic agents — bleeding may occur. CYP-450 enzyme-mediated herbal drug interactions are possible; caution should be exercised.

CYP450 Enzyme Interactions

Studies have demonstrated that resveratrol can interact with drugs metabolized by UGT1A1, CYP1A2, CYP2C19, CYP2E1, and CYP3A. Grape seed may increase the serum concentration of dextromethorphan; this interaction is documented as requiring no specific action in the cited literature, but CYP-enzyme-mediated interactions remain a general caution.

Hypoglycemia Risk

There is a theoretical risk of hypoglycemia when GSE is combined with insulin or sulphonylureas such as gliclazide.

Hepatotoxicity

In large case series and nationwide registries on herbal-induced liver injury, resveratrol is not listed as a cause. Thus, hepatotoxicity due to resveratrol must be rare, if it occurs at all. Likelihood score: E (unlikely cause of clinically apparent liver injury).

Pregnancy and Lactation

Grape seed is contraindicated in individuals with known hypersensitivity to grape products. Information regarding safety and efficacy in pregnancy and lactation is lacking.

Bioavailability Limitations

A major hurdle of dietary polyphenols includes their poor water solubility and oral bioavailability. Resveratrol has low systemic bioavailability and is not well-absorbed orally. This pharmacokinetic limitation is a persistent challenge in translating preclinical findings to human clinical benefit.

Context-Dependent Effects in Cancer Models

Animal study findings implicate low concentrations of resveratrol in potential promotion of breast cancer, underscoring the importance of further delineating resveratrol's concentration-dependent effects, particularly in breast cancer, before it can be used as a dietary supplement for breast cancer patients. This represents an important unresolved safety question that warrants further human research.

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