Polyphenols, Quercetin and Resveratrol
Polyphenols, quercetin, resveratrol and grape seed extract: what reviews found for blood pressure, blood vessels and skin, and why most claims go beyond the evidence.
Content last updated . This page has not been medically reviewed.
Overview
Polyphenols are a large family of plant compounds. Quercetin is described as the most abundant dietary flavonol. [1] Grape seed extract contains proanthocyanidins. [2] Resveratrol is another plant compound sold as a supplement. There is no recommended intake or deficiency syndrome for any of these in the sources read, and different compounds are not interchangeable. Evidence labels are explained on Antioxidants Explained.Green tea catechins are covered on green tea and curcumin on turmeric and curcumin supplements. Resveratrol longevity claims at goal level are on NAD, NMN and longevity claims.
Evidence by compound
| Compound | What the sources found | Label |
|---|---|---|
| Quercetin | A meta-analysis of 7 trials (587 people) found small reductions in blood pressure: systolic about 3.0 mm Hg, diastolic about 2.6 mm Hg, possibly limited to 500 mg a day or more (study amounts). [1] A 2023 umbrella review found a lower systolic pressure (about 1.9 mm Hg) and insulin level but no effect on diastolic pressure, lipids or fasting glucose. [3] | Promising but limited |
| Resveratrol, blood vessels | A meta-analysis of 17 studies found improved flow-mediated dilation (a measure of artery function) but several other markers did not change. [4] | Biomarker only |
| Resveratrol, older adults | A review of 10 trials found mixed results: some benefit with exercise, no better than placebo in older adults with diabetes or peripheral artery disease, and higher doses raised some cardiovascular risk biomarkers; no significant adverse events were reported. [5] | Mixed |
| Grape seed extract | A 2020 review of 11 studies suggested lower LDL cholesterol and triglycerides; a 2022 review of 19 studies found lower diastolic but not systolic pressure; the NCCIH says the conclusions are not definite because studies were small and products varied. [2] | Promising but limited |
| Skin sun protection (polyphenols and carotenoids) | A review of 47 studies found the greatest photoprotection evidence for polyphenols, carotenoid supplements and Polypodium leucotomos, limited by small, short studies. [6] | Promising but limited |
| Pycnogenol and other branded extracts | Proper evidence not found in the sources checked for this page. | Insufficient evidence |
Food versus supplements
Polyphenols come in foods such as tea, berries and cocoa; see Nutrients and compounds in foods and blueberries. A trial of a purified compound does not tell you what the food does, and the reverse is also true: the NCCIH notes that purified antioxidants may act differently from those in foods. [7]Safety
The NCCIH says grape seed extract is generally well tolerated, with little known about pregnancy or breastfeeding. [2] The resveratrol review above reported no significant adverse events but noted that optimal dosage and long-term effects are unclear. [5] Proper evidence not found in the sources read for quercetin safety, interactions or upper limits. Antioxidant supplements in general may interfere with cancer treatment; see antioxidant safety and marketing claims, medication interactions and reading supplement labels.Frequently asked questions
Does quercetin lower blood pressure?
Meta-analyses found small reductions, but the clinical meaning is unclear. [1][3]
Does resveratrol slow aging?
Proper evidence not found for slowed aging in humans in the sources read; results in older adults were mixed. [5]
Is grape seed extract safe?
The NCCIH says it is generally well tolerated; pregnancy safety is unknown. [2]
Are polyphenol supplements better than polyphenol-rich foods?
Proper evidence not found; the sources read compared supplements with placebo, not with food.
References
- Serban et al., Effects of quercetin on blood pressure: systematic review and meta-analysis (J Am Heart Assoc 2016). Read 2026-10-22.
- NCCIH, Grape Seed Extract. Read 2026-10-22.
- The effects of quercetin supplementation on cardiometabolic outcomes: umbrella review (Phytother Res 2023). Read 2026-10-22.
- Resveratrol supplementation improves endothelial health: systematic review and meta-analysis (Phytother Res 2022). Read 2026-10-22.
- Effects and safety of resveratrol supplementation in older adults: a comprehensive systematic review (Phytother Res 2024). Read 2026-10-22.
- Natarelli et al., Oral supplements and photoprotection: a systematic review (J Med Food 2025). Read 2026-10-22.
- NCCIH, Antioxidant Supplements: What You Need To Know. Read 2026-10-22.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.