Polyphenols and Flavonoids in Foods: Berries, Cocoa, Tea and Olive Oil
What polyphenols and flavonoids are, which foods contain them, what trials of berries, cocoa and citrus found, and why antioxidant supplements do not reproduce food results.
Content last updated . This page has not been medically reviewed.
Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
Short answer: Polyphenols are a large family of plant compounds, and flavonoids are one group within it. Trials of flavonoid-rich foods show small, inconsistent changes in blood-vessel markers, and a high polyphenol count on a label does not guarantee a health effect.
What the terms mean
Flavonoids are described in one review as "a type of polyphenol abundant in fruits". [1] Foods commonly studied include blueberries (Vaccinium corymbosum), cocoa (Theobroma cacao), tea (Camellia sinensis), citrus and olive oil (Olea europaea). [2] Each of these foods has its own page: blueberries, dark chocolate and cocoa, green and black tea and extra virgin olive oil.
What research shows
| Question | What the source found | Strength of evidence | Population and form |
|---|---|---|---|
| Flavonoid-rich foods and blood-vessel function | A meta-analysis of 11 randomized trials (561 healthy adults) found improved flow-mediated dilation; blood pressure did not change significantly. [3] | Promising but limited (marker, high heterogeneity) | Healthy adults, various foods |
| Wild blueberry powder | A 12-week double-blind trial in 61 older adults found improved dilation and lower 24-hour systolic pressure (-3.59 mmHg) versus placebo. [4] | Promising but limited (one trial) | Adults 65 to 80, freeze-dried powder |
| Flavonoid-rich fruit and hypertension | A systematic review of 15 trials found no effect of flavonoids on systolic or diastolic pressure in the four-trial pooled analysis. [1] | Mixed | Adults with hypertension |
| Hesperidin (citrus flavonoid) | A meta-analysis of 10 trials found no effect on cholesterol or blood pressure. [5] | No good evidence of benefit | Supplement trials |
| Cocoa flavanol extract | In a trial of 21,442 older adults, the standard analysis of cardiovascular events was nonsignificant, while a re-analysis weighting event severity favored cocoa extract. [6] | Mixed | Older adults, an extract and not chocolate |
Two points matter when reading these. First, the cocoa trial tested an extract. Chocolate also contains sugar, fat and calories, so its results do not carry over (see the dark chocolate page). Second, several results above are for supplements or powders, not whole berries or citrus.
Antioxidant supplements are not the same as antioxidant foods
Foods rich in polyphenols are often called antioxidant-rich, but the trials above measured blood-vessel markers, not antioxidant activity. For antioxidant vitamin and mineral supplements, a large Cochrane review of 78 trials found no overall effect on death in one analysis and higher mortality in the 56 low-risk-of-bias trials. It found that beta-carotene and vitamin E increased mortality, while vitamin A, vitamin C and selenium did not. [7] Those were supplements of specific vitamins, not polyphenol foods. See antioxidants explained for the supplement side.
Limits
- Most food trials are short and use markers.
- Different studies use different amounts, forms and comparison foods, so results cannot be added up simply.
- Population studies of berry or tea intake can reflect lifestyle differences. See observational studies versus trials.
Frequently asked questions
Does a food with more polyphenols work better?
We did not find a source showing that higher polyphenol content on its own predicts a larger effect. A hesperidin review found no effect on lipids or blood pressure. [5]
Do blueberries lower blood pressure?
In one 12-week trial in older adults, daily freeze-dried wild blueberry powder lowered 24-hour systolic pressure by 3.59 mmHg compared with placebo. [4] A systematic review of flavonoid-rich fruits found no effect on blood pressure in pooled hypertension trials. [1]
Is dark chocolate good for the heart?
The large trial we read tested cocoa extract and not chocolate, and results depended on how events were analyzed. [6] See the dark chocolate page for sugar and caffeine.
Can an antioxidant supplement replace fruit and vegetables?
We found no source showing that. The Cochrane review of antioxidant supplements found increased mortality for beta-carotene and vitamin E in low-risk-of-bias trials. [7]
Which polyphenol food is best?
Proper evidence not found. We searched PubMed for head-to-head trials of flavonoid-rich foods and read only the reviews cited here, none of which ranks foods.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask a clinician
Whole polyphenol foods have food-specific cautions, such as the grapefruit and medicine point on the citrus page and caffeine in tea, cocoa and coffee. Concentrated polyphenol extracts and capsules can behave differently from foods; check the label and see quality testing and certifications. The sources we read for this page did not describe medicine interactions of polyphenol extracts, so ask a pharmacist, and read How Interactions Work.
References
- Effects of flavonoid-rich fruits on hypertension in adults: a systematic review. JBI Database System Rev Implement Rep 2019. PMID 31464854. Read 2026-10-23.
- GBIF Backbone Taxonomy species match. Global Biodiversity Information Facility. Accepted names checked 2026-10-23.
- Flavonoid-rich foods and vascular functions in healthy adults: a systematic review and meta-analysis of randomized controlled trials. Food Funct 2026. PMID 42720125. Read 2026-10-23.
- Wild blueberry (poly)phenols can improve vascular function and cognitive performance in healthy older individuals: a double-blind randomized controlled trial. Am J Clin Nutr 2023. PMID 36972800. Read 2026-10-23.
- Hesperidin, a major flavonoid in orange juice, might not affect lipid profile and blood pressure: a systematic review and meta-analysis of randomized controlled clinical trials. Phytother Res 2019. PMID 30632207. Read 2026-10-23.
- Cocoa flavanol supplementation and prevention of cardiovascular disease: a novel analysis of the COSMOS randomized trial using "win ratio". Eur J Epidemiol 2026. PMID 41849087. Read 2026-10-23.
- Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2012. PMID 22419320. Read 2026-10-23.