The EPIC cohort and colorectal cancer: what polyphenol data from 500,000 people shows
Randomised controlled trials are the gold standard for establishing causation in medicine. But for questions about diet and cancer — where exposures unfold over decades and no trial can ethically randomise people to eat poorly for thirty years — large prospective cohort studies are often the best available evidence. Few cohort studies have been more influential in cancer nutrition research than the European Prospective Investigation into Cancer and Nutrition, known as EPIC.
Launched in the 1990s and involving over half a million participants across ten European countries, EPIC has generated hundreds of papers on the relationship between diet, lifestyle, and cancer. One of the most relevant to this series is a 2018 analysis by Zamora-Ros and colleagues, published in the European Journal of Epidemiology, which examined the relationship between dietary polyphenol intake and colorectal cancer risk across the EPIC cohort.
What is EPIC
The EPIC study enrolled 521,448 people aged 35 to 70 across ten countries — France, Italy, Spain, the United Kingdom, the Netherlands, Greece, Germany, Sweden, Denmark, and Norway. Participants completed detailed dietary questionnaires at recruitment, alongside lifestyle and health questionnaires, and have been followed up for cancer incidence and mortality for over two decades.
The scale and diversity of EPIC makes it uniquely suited to studying diet-cancer relationships. The wide variation in dietary patterns across European populations creates the dietary contrast needed to detect associations between specific foods, nutrients, and cancer outcomes.
The Zamora-Ros polyphenol analysis
The 2018 study analysed data from 476,160 EPIC participants, following them for a mean of 14 years, during which 4,517 cases of colorectal cancer were diagnosed. Dietary polyphenol intake was estimated using detailed food frequency questionnaires combined with the Phenol-Explorer database — a comprehensive database of polyphenol content in foods — allowing total polyphenol intake and intake by polyphenol class to be calculated for each participant.
The analysis examined both total polyphenol intake and intake of specific polyphenol subclasses: flavonoids, phenolic acids, stilbenes, lignans, and other polyphenols. Colorectal cancer risk was assessed separately for colon and rectal cancer, and for men and women.
What the analysis found
Higher total dietary polyphenol intake was associated with a modestly but significantly reduced risk of colorectal cancer across the EPIC cohort. When the cohort was divided into fifths by polyphenol intake, those in the highest fifth had a lower risk of colorectal cancer compared to those in the lowest fifth, after adjusting for a wide range of potential confounders including age, sex, smoking, physical activity, body mass index, alcohol intake, and total calorie intake.
When polyphenol subclasses were examined, lignans showed the most consistent inverse association with colorectal cancer risk. Lignans are polyphenols found primarily in flaxseeds, sesame seeds, wholegrains, and some vegetables and fruits. They are metabolised by gut bacteria into enterolignans, which may influence colorectal cancer risk through effects on the gut microbiome and intestinal inflammation.
Why polyphenols might protect against colorectal cancer
Anti-inflammatory effects. NF-κB-driven chronic inflammation is a well-characterised driver of colorectal carcinogenesis. Multiple polyphenols inhibit NF-κB signalling in laboratory models, and the 2024 Journal of Nutrition data from Dryer-Beers and colleagues found that higher dietary polyphenol intake was associated with lower blood inflammatory markers in a human cohort — supporting the relevance of this mechanism in people.
Gut microbiome modulation. Dietary polyphenols are substrates for gut bacteria — they are fermented in the colon, producing bioactive metabolites including short-chain fatty acids and enterolignans that influence colonocyte health and the inflammatory environment of the colon. Higher polyphenol intake supports a more diverse gut microbiome, which is itself associated with lower colorectal cancer risk.
Antioxidant activity. Polyphenols are potent antioxidants in laboratory conditions, though the extent to which dietary antioxidants reduce oxidative DNA damage in human colonic tissue is debated. The direct antioxidant mechanism is likely less important than the anti-inflammatory and microbiome-mediated effects in explaining the epidemiological association.
The limitations of cohort data
The EPIC polyphenol analysis is an observational study. It cannot establish causation — it can only identify associations. People who eat more polyphenols may differ from those who eat fewer in ways that affect colorectal cancer risk independently of polyphenols. Although the EPIC analysis adjusted for many of these factors, residual confounding cannot be excluded.
The effect sizes in the EPIC polyphenol analysis are modest — this is not a finding of a dramatic protective effect, but a consistent directional signal across a very large population with excellent statistical power to detect small associations.
What the evidence means for diet in practice
Polyphenol-rich foods are already the building blocks of a cancer-protective diet. The foods that contribute most to polyphenol intake in European populations are tea, coffee, fruits (especially berries, apples, and citrus), vegetables (especially onions and dark leafy greens), wholegrains, nuts, and seeds. A dietary pattern built around abundant plant variety naturally delivers high polyphenol intake without any need for supplementation.
Lignans specifically are worth prioritising. Given the consistency of the lignan-colorectal cancer association in the EPIC data, foods rich in lignans — flaxseeds, sesame seeds, wholegrain rye, and lentils — are worth including regularly. Ground flaxseed added to porridge, yoghurt, or smoothies is one of the most practical ways to increase lignan intake.
Diversity matters as much as quantity. Different polyphenol subclasses act through different mechanisms and reach different tissues. A dietary pattern that includes a wide variety of colourful fruits and vegetables, wholegrains, legumes, nuts, seeds, tea, and herbs delivers the broadest spectrum of polyphenol activity.
Supplements are not a substitute. The EPIC association is with dietary polyphenol intake from whole foods — not with polyphenol supplements. The matrix of whole foods delivers fibre, micronutrients, and other bioactive compounds alongside polyphenols, and the interactions between these components are part of what makes whole food patterns protective.
What the evidence does not show
The EPIC analysis cannot establish that polyphenols are causally responsible for the reduced colorectal cancer risk observed in high-polyphenol consumers. There is also no evidence from randomised controlled trials that increasing polyphenol intake through dietary change reduces colorectal cancer incidence — such a trial would require decades of follow-up and is not feasible.
The bottom line
The EPIC cohort analysis of polyphenol intake and colorectal cancer risk — 476,160 participants, 14 years of follow-up, 4,517 colorectal cancer cases — found a consistent inverse association between dietary polyphenol intake, particularly lignan intake, and colorectal cancer risk. The effect sizes are modest, the study is observational, and causation cannot be established. But the finding is biologically plausible, consistent with the mechanistic literature on polyphenols and colonic inflammation, and supported by the broader evidence that plant-rich dietary patterns are associated with lower colorectal cancer risk. Eating abundantly and diversely from plant sources — prioritising variety, colour, and whole foods over supplements — remains the most evidence-consistent dietary strategy for colorectal cancer prevention.
Scientific references
- Zamora-Ros R, et al. Dietary intake of total polyphenol and polyphenol classes and the risk of colorectal cancer in the EPIC cohort. European Journal of Epidemiology. 2018. PMID: 29761424. DOI: 10.1007/s10654-018-0408-6
- Dryer-Beers ER, et al. Higher dietary polyphenol intake is associated with lower blood inflammatory markers. Journal of Nutrition. 2024. PMID: 38740187. DOI: 10.1016/j.tjnut.2024.05.005
- Patel AV, et al. American Cancer Society guideline for diet and physical activity for cancer prevention. CA: A Cancer Journal for Clinicians. 2020;70(4):245–271. DOI: 10.3322/caac.21591
This article is written for educational and informational purposes only. It is not intended as medical advice and should not be used to diagnose, treat, prevent, or cure any medical condition, including cancer. If you have a cancer diagnosis or are undergoing treatment, please discuss any lifestyle or dietary changes with your oncologist or medical team before making them. The studies cited reflect current research at the time of writing; the field is evolving rapidly and findings may be updated or superseded. Chloe Archard is a nutritional health coach, not a medical doctor.
