Procyanidins and OPCs

1. What This Class of Substances Is

Procyanidins and OPCs (oligomeric proanthocyanidins) are oligomeric flavonoids composed of catechin and epicatechin units. They are found in plant materials such as cocoa, grape seeds, pine bark, coffee fruit, and berries. Chemically, they belong to the polyphenols and exhibit antioxidant properties. Their structure varies depending on the degree of polymerisation and type of bonding, which influences their bioavailability and effects. Natural sources often contain mixtures of monomers, oligomers, and polymers, making standardisation challenging.

The effects of procyanidins in humans are difficult to measure directly, as they undergo extensive metabolism following oral intake. In the gut, breakdown products such as phenolic acids are formed, whose effects may differ from those of the parent compounds. Additionally, bioavailability varies between individuals, depending on gut microbiome and genetics. Controlled studies therefore often use standardised extracts to achieve reproducible results. Nevertheless, the applicability to natural foods remains limited.

2. Which Materials Are Included

All substances in the database for which this mechanism of action is described—ordered by the extent of human testing. The numbers represent studies per type of investigation.

3. How Robust the Evidence Is

Cocoa flavanols and grape seed extract (OPC) are the most extensively studied in humans, with over 30 controlled trials each. Pine bark extract and anthocyanins (berries) follow with significantly fewer but existing human studies. Coffee fruit extract and other sources are scarcely tested. Laboratory and animal studies predominate for all substances, indicating an early stage of research. Particularly for coffee fruit extract and pine bark, there is a lack of robust data on long-term effects.

Procyanidins and OPC share similar chemical structures and antioxidant mechanisms. Findings on cocoa or grape seeds suggest that other sources may also have anti-inflammatory or vascular-protective effects. However, the degree of polymerisation, accompanying substances, and bioavailability vary between sources. Therefore, extrapolating the results is hypothetical. For example, there are no studies directly comparing whether pine bark OPC has similar effects to grape seed OPC.

4. Key Human Studies

• 1 Antiobesity effects of green tea catechins: a mechanistic review (2011) — Green tea and EGCG
• 2 Potential role of green tea catechins in various disease therapies: progress and promise (2012) — Green tea and EGCG
• 3 Randomized, Placebo-Controlled Trial of Green Tea Catechins for Prostate Cancer Prevention (2015) — Green tea and EGCG
• 4 Flavonoid-rich dark chocolate improves endothelial function and increases plasma epicatechin concentrations in healthy adults (2004) — Cocoa flavanols
• 5 Chronic ingestion of flavan-3-ols and isoflavones improves insulin sensitivity and lipoprotein status and attenuates estimated 10-year CVD risk in med (2012) — Cocoa flavanols
• 6 Effect of cocoa flavanol supplementation for the prevention of cardiovascular disease events: the COcoa Supplement and Multivitamin Outcomes Study … (2022) — Cocoa flavanols
• 7 Effects of grape seed proanthocyanidin extract on menopausal symptoms, body composition, and cardiovascular parameters in middle-aged women: a randomi (2014) — Grape seed extract (OPC)
• 8 Two apples a day lower serum cholesterol and improve cardiometabolic biomarkers in mildly hypercholesterolemic adults: a randomized, controlled, cross (2020) — Grape seed extract (OPC)
• 9 Effects of Grape Seed Proanthocyanidin Extract on Vascular Endothelial Function in Participants with Prehypertension: A Randomized, Double-Blind, Plac (2019) — Grape seed extract (OPC)
• 10 Polyphenol Intervention Ameliorates Non-Alcoholic Fatty Liver Disease: An Updated Comprehensive Systematic Review (2024) — Turmeric and curcumin
• 11 Effects of Dietary Components on Mast Cells: Possible Use as Nutraceuticals for Allergies? (2023) — Turmeric and curcumin
• 12 Potential Effects of Bioactive Compounds of Plant-Based Foods and Medicinal Plants in Chronic Kidney Disease and Dialysis: A Systematic Review (2024) — Turmeric and curcumin
• 13 Treatment of ADHD with French maritime pine bark extract, Pycnogenol (2006) — Pine bark extract
• 14 Pycnogenol, French maritime pine bark extract, augments endothelium-dependent vasodilation in humans (2007) — Pine bark extract
• 15 Effects of low molecular weight procyanidin rich extract from french maritime pine bark on cardiovascular disease risk factors in stage-1 hypertensive (2016) — Pine bark extract
• 16 A Randomized, Placebo-Controlled Study on the Safety and Efficacy of Daily Ingestion of Green Tea (<i>Camellia sinensis</i> L.) cv. "Yabukita" and "Su (2018) — Anthocyanins (berries)
• 17 The Effect of Antioxidant Polyphenol Supplementation on Cardiometabolic Risk Factors: A Systematic Review and Meta-Analysis (2024) — Anthocyanins (berries)
• 18 Immunomodulatory Effects of Aronia Juice Polyphenols—Results of a Randomised Placebo-Controlled Human Intervention Study and Cell Culture Experiments (2022) — Anthocyanins (Berries)
• 19 Effects of 2-Year Cocoa Extract Supplementation on Inflammaging Biomarkers in Older US Adults: Findings from the COcoa Supplement and Multivitamin Outcomes (COSMOS) Trial (2025) — Chronic Inflammation
• 20 Nutraceutical Enhancement of Paraoxonase 1 Activity in Chronic Inflammation: A Systematic Review of Animal-Based and Plant-Based Nutraceuticals (2026) — Chronic Inflammation
• 21 Effect of Epigallocatechin Gallate Supplementation on Inflammation, Iron Status, and Metabolomic Profiles in Women with Obesity: A Pilot Randomised Controlled Trial (2026) — Chronic Inflammation
• 22 Botanicals and Phytochemicals Active on Cognitive Decline: The Clinical Evidence (2018) — Adaptogens
• 23 Natural Health Products That Inhibit Angiogenesis: A Potential Source for Investigational New Agents to Treat Cancer—Part 2 (2006) — Adaptogens
• 24 Approaches to Field Cultivation of Rhodiola kirilowii and Rhodiola rosea in Poland and Their Potential Health Benefits (2015) — Adaptogens

5. Open Questions

• Standardisation: How can extracts from different sources (cocoa, grape seeds, pine bark) be characterised in a comparable manner to assess differences in efficacy?
• Bioavailability: What role does the gut microbiome play in the metabolism of procyanidins, and how does this affect their impact in humans?
• Long-Term Effects: Are there robust data on the chronic intake of procyanidin extracts, particularly from coffee fruit or pine bark?
• Combination Effects: Do procyanidins from different sources act synergistically, or do their effects overlap?
• Target Groups: Which patient groups (e.g., those with metabolic syndrome or chronic inflammation) benefit most from procyanidins, and how does the effect vary?

See also the gap list covering all substances. This page is recalculated with each update.