Why dietary polyphenols lower inflammation: the 2024 Journal of Nutrition data
Earlier in this series, we looked at the EPIC cohort’s finding that higher dietary polyphenol intake is associated with reduced colorectal cancer risk. One of the most important questions underlying that finding is mechanism: how, precisely, does eating more polyphenol-rich foods translate into a lower-risk environment for cancer?
A 2024 study published in the Journal of Nutrition by Dryer-Beers and colleagues provides some of the clearest human evidence yet on that mechanism — specifically the link between dietary polyphenol intake and circulating inflammatory markers in a large population sample.
The study
The Dryer-Beers 2024 analysis examined the relationship between dietary polyphenol intake and blood inflammatory markers in a community-based cohort of adults. Dietary intake was assessed using validated dietary assessment tools, with polyphenol content estimated using the Phenol-Explorer database. Inflammatory markers measured included high-sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), and tumour necrosis factor-alpha (TNF-α) — three of the most clinically relevant circulating markers of systemic low-grade inflammation.
The study is notable for its use of multiple inflammatory markers rather than a single measure, and for its focus on dietary polyphenol intake from whole foods rather than supplement use.
What the study found
Higher dietary polyphenol intake was significantly associated with lower levels of all three inflammatory markers — hsCRP, IL-6, and TNF-α — after adjusting for age, sex, body mass index, smoking, physical activity, and other dietary factors. The association was dose-dependent: participants with the highest polyphenol intake had the lowest inflammatory marker levels, and those with the lowest polyphenol intake had the highest.
The association was consistent across polyphenol subclasses, with flavonoids and phenolic acids — the two most abundantly consumed subclasses — both showing significant inverse associations with inflammatory markers. This is human population evidence that what people eat in their everyday lives is directly reflected in their systemic inflammatory profile.
Why inflammation matters for cancer
Chronic low-grade inflammation is one of the most consistently identified features of cancer-permissive biology. NF-κB-driven inflammatory signalling promotes tumour initiation, progression, and metastasis through multiple converging pathways: creating a pro-proliferative tissue microenvironment, suppressing immune surveillance, and promoting angiogenesis.
The inflammatory markers reduced by higher polyphenol intake in the Dryer-Beers study are active participants in tumour biology. IL-6 activates STAT3 signalling in cancer cells, promoting their survival and resistance to apoptosis. Elevated hsCRP is a robust epidemiological predictor of cancer risk across multiple cancer types. Reducing circulating levels of these markers through diet is, in biological terms, directly relevant to cancer risk.
The mechanisms: how polyphenols reduce inflammation
NF-κB inhibition. Multiple polyphenols — including quercetin (found in onions, apples, and tea), resveratrol (found in red grapes and berries), and EGCG (found in green tea) — inhibit NF-κB activation, the master regulator of the inflammatory response.
Nrf2 activation. Polyphenols activate the Nrf2 transcription factor, which drives expression of antioxidant and cytoprotective enzymes, reducing the oxidative load that feeds inflammatory pathways.
Gut microbiome effects. A substantial proportion of dietary polyphenols reach the colon unabsorbed, where they serve as substrates for gut bacteria. Polyphenol fermentation produces short-chain fatty acids — including butyrate — that have direct anti-inflammatory effects on colonocytes and on systemic immune function.
Eicosanoid modulation. Polyphenols including quercetin and luteolin inhibit cyclooxygenase (COX) and lipoxygenase enzymes, reducing the production of pro-inflammatory eicosanoids including prostaglandins and leukotrienes.
Which foods to prioritise
Quercetin-rich foods — onions (especially red onions), apples, and tea — are among the richest dietary sources of this well-studied anti-inflammatory flavonoid. Bioavailability is higher when consumed raw or lightly cooked.
Green tea provides EGCG, one of the most studied anti-inflammatory polyphenols. Two to four cups per day represents a practical and well-tolerated intake level.
Berries — blueberries, blackberries, raspberries, and strawberries — are exceptionally rich in anthocyanins, with particularly potent NF-κB inhibitory effects. Fresh and frozen are equivalent in polyphenol content.
Extra virgin olive oil contains oleocanthal, a phenolic compound that inhibits both COX-1 and COX-2. The anti-inflammatory effects of the Mediterranean diet are partly attributable to oleocanthal intake.
Dark chocolate (70% cocoa or above) is a significant source of flavanols with well-documented anti-inflammatory effects in human trials.
What this means in practice
Anti-inflammatory eating is not a supplement protocol. The Dryer-Beers findings relate to whole food polyphenol intake. A polyphenol supplement providing isolated quercetin or resveratrol does not replicate the synergistic effects of whole food polyphenol combinations consumed alongside fibre, healthy fats, and other bioactive compounds.
Frequency and consistency matter more than quantity on any given day. The association reflects habitual dietary polyphenol intake — what people eat over weeks and months. Building polyphenol-rich foods into daily habits is more meaningful than occasional high-dose consumption.
What the evidence does not show
The Dryer-Beers study is observational — it cannot establish that polyphenols causally reduce inflammatory markers. People who eat more polyphenols may differ from those who eat fewer in ways that independently affect inflammation. Randomised controlled trials of polyphenol interventions on inflammatory markers exist and are generally supportive, but most are short-term and use supplements rather than whole foods.
The bottom line
The 2024 Dryer-Beers Journal of Nutrition study demonstrates a consistent, dose-dependent inverse association between habitual dietary polyphenol intake and circulating inflammatory markers — hsCRP, IL-6, and TNF-α — in a population cohort. This is human evidence that what we eat is directly reflected in our systemic inflammatory profile. Given that chronic low-grade inflammation is a well-established driver of cancer biology, reducing it through a polyphenol-rich dietary pattern is a biologically coherent and practically achievable strategy. The foods involved — berries, onions, apples, green tea, extra virgin olive oil, wholegrains, dark chocolate — are neither exotic nor expensive. They are the foundation of any genuinely cancer-protective diet.
Scientific references
- 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
- 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
- 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.
