Flavanols are the plant compounds in cocoa, tea, apples and grapes that relax blood vessels. An expert panel puts the useful range at 400 to 600 mg a day, from food. The largest trial ever run on a cocoa flavanol supplement missed its primary endpoint. Both of those things are true, and neither is on the packet.
What are flavanols?
Flavanols, properly flavan-3-ols, are one branch of the flavonoid family. The small ones are the monomers: catechin, epicatechin, and their gallate forms, epigallocatechin gallate among them. Join monomers together and you get procyanidins, which are the bulk of what cocoa actually contains and which behave quite differently in the gut.
They are the compounds behind astringency. That dry, gripping sensation from strong tea, an unripe apple or a young red wine is flavanols binding to the proteins in your saliva. It is a reasonably good field test: if a plant food makes your mouth feel tight, it carries them.
What they do in the body is better defined than for most polyphenols. The best documented action is on the endothelium, the single cell lining of your blood vessels, where flavanol metabolites increase nitric oxide availability and the vessel widens. That is measurable, it is reproducible, and it is why this group of compounds has a regulatory status that other polyphenols do not.
Flavanols or flavonols? One letter, two different compounds
This trips up supplement labels, journalists and search engines equally, so it is worth thirty seconds.
FLAVANOLS
Flavan-3-ols. Catechin, epicatechin, procyanidins. Cocoa, tea, apples, grapes, broad beans. This article.
FLAVONOLS
Quercetin, kaempferol, myricetin. Onions, kale, capers, tea. A different branch, with different evidence.
FLAVONOIDS
The family that contains both, plus anthocyanins, flavones and isoflavones. The word to use when you mean all of them.
So quercetin is not a flavanol, and the epigallocatechin gallate in green tea is not a flavonol. If a product page uses the two words as synonyms, it has not read its own evidence.
Which foods are richest in flavanols?
Cocoa leads on concentration, but the ranking that matters is what you actually drink and eat in a week. In a British diet, tea does more of the work than anything else.
| Food or drink | Main flavanols | Notes that change the number |
|---|---|---|
| Cocoa powder, non-alkalised | Epicatechin, procyanidins | Dutch processing with alkali strips most of the flavanols out |
| Dark chocolate, 70 per cent and above | Epicatechin, procyanidins | Milk chocolate carries a fraction of it |
| Green tea | EGCG, epicatechin, catechin | Brewing time matters more than leaf grade |
| Black tea | Theaflavins, thearubigins, some catechins | Oxidation converts catechins into larger compounds |
| Apples, skin on | Epicatechin, procyanidins | Peeling removes a large share |
| Red grapes and red wine | Catechin, procyanidins | Present in skins and pips, so red only |
| Broad beans, blackcurrants, blackberries | Procyanidins | Underrated, and seasonal in Britain |
Two practical points. Cocoa content on a wrapper is not flavanol content, because processing decides that and nobody prints it. And a mug of ordinary brewed tea, drunk four or five times a day as most of this country does, quietly beats an occasional square of expensive chocolate. The same cup carries more than one measured compound: L-theanine was measured at 24.2 mg in a 200 ml cup of black tea, against 7.9 mg in green.
How much do you need, and what a UK label may claim?
In 2022 an expert panel convened under the Academy of Nutrition and Dietetics process published the first dietary guideline ever written for a plant bioactive rather than a nutrient. Crowe-White and colleagues, with Gunter Kuhnle of the University of Reading among the authors, drew on 157 randomised controlled trials and 15 cohort studies.
Their conclusion: moderate evidence supports cardiometabolic benefit from flavan-3-ol intake in the range of 400 to 600 mg a day, with the strongest evidence for systolic blood pressure, total and HDL cholesterol, and insulin and glucose dynamics. The panel stated plainly that this is a food based guideline and not a recommendation for flavan-3-ol supplements.
Separately, and at a much lower dose, one flavanol claim is authorised for use on labels in Great Britain. Cocoa flavanols may be said to help maintain endothelium-dependent vasodilation, which contributes to normal blood flow. The condition is 200 mg of cocoa flavanols a day, which the assessment says can be provided by 2.5 g of high-flavanol cocoa powder or 10 g of high-flavanol dark chocolate.
That is the whole of what a British label is allowed to say about flavanols. Anything about memory, ageing, inflammation or antioxidant protection is outside the authorisation, whatever the research suggests.
What happens after you drink them
Flavanols are often described as poorly absorbed. For the monomers, that is wrong, and the study that settled it is unusually clean. Ottaviani and colleagues gave eight people radiolabelled epicatechin, 60 mg of it, and followed every carbon atom.
of ingested epicatechin was absorbed, plus or minus 5 per cent. It appeared in the blood as more than 20 different metabolites, not as epicatechin.
Ottaviani et al., Scientific Reports, 2016, radiolabelled study in 8 adults
Three things follow. The compound is absorbed, so poor bioavailability is not the objection. It is transformed on the way, so whatever acts in your blood vessels is a metabolite rather than the molecule on the ingredient list. And the gut microbiome proved to be a key driver of that metabolism, which is part of why two people drinking the same tea end up with different profiles.
The same paper flagged striking species dependent differences in epicatechin metabolism, which is a quiet warning about every rodent study in this field. What a mouse makes from a flavanol is not what you make from it.
The procyanidins are a different story. Being larger, most of them are not absorbed intact at all and travel to the colon, where bacteria break them into smaller phenolic acids. This is the same absorption question that decides whether any concentrated plant extract does anything, and the reason a turmeric formulation built for absorption is argued on pharmacokinetics rather than on milligrams.
What the COSMOS trial actually showed
Everything above rests on biomarkers. The question nobody could answer until recently was whether any of it prevents heart attacks. COSMOS, the Cocoa Supplement and Multivitamin Outcomes Study, was built to find out.
Sesso and colleagues randomised 21 442 older adults in the United States, 12 666 women aged 65 and over and 8 776 men aged 60 and over, to a cocoa extract supplying 500 mg of flavanols a day including 80 mg of epicatechin, or to placebo. Median follow-up was 3.6 years.
The primary outcome, total cardiovascular events, gave a hazard ratio of 0.90 with a confidence interval of 0.78 to 1.02 and a P value of 0.11. That does not reach significance. The trial did not show that cocoa extract prevents cardiovascular events, and any page that says otherwise is quoting the wrong line.
The secondary endpoints are where it becomes interesting. Cardiovascular death fell, hazard ratio 0.73 with an interval of 0.54 to 0.98, a 27 per cent reduction. A per-protocol analysis that censored follow-up at non-adherence gave 0.85 for total cardiovascular events, interval 0.72 to 0.99. There were no safety concerns. All-cause mortality was 0.89, interval 0.77 to 1.03.
A secondary endpoint in a trial that missed its primary one generates a hypothesis, not a conclusion. What COSMOS honestly supports is that a cocoa flavanol supplement is safe at that dose over three and a half years, that it did not deliver the effect it was designed to detect, and that something in the cardiovascular death data is worth another trial.
Getting to 500 mg a day from food
Set against the trial, the observational data are more encouraging and less conclusive, as observational data always are. Bondonno and colleagues followed 56 048 people in the Danish Diet, Cancer and Health cohort for 23 years and recorded 14 083 deaths. A moderate habitual intake of total flavonoids was inversely associated with all-cause, cardiovascular and cancer mortality, and the association plateaued at around 500 mg a day. That is the shape the rest of the diet and mortality literature takes as well, where the modelled gains in life expectancy come from ordinary food groups rather than from extracts.
Two details make that study more useful than most. The plateau means there is no benefit to chasing very high intakes. And the inverse association was stronger and more linear in smokers, and in people drinking more than 20 g of alcohol a day, than in everyone else. The people with the most oxidative and inflammatory burden are the ones the data favours most, which is a coherent finding rather than a convenient one.
Reaching a few hundred milligrams a day is not difficult in a British diet, and needs nothing bought specially.
- Four or five mugs of tea. Green or black, both count. This is the single largest contribution for most people here.
- An apple with the skin on. Peeling it removes much of the point.
- Two squares of dark chocolate at 70 per cent or above, or a spoon of non-alkalised cocoa powder in porridge. Check the ingredient list for the word alkalised and avoid it.
- Red grapes, blackberries or blackcurrants when they are about.
- Broad beans, which nobody thinks of and which are a genuinely good source.
None of this is a treatment. If you are managing blood pressure, the medication and the sodium and potassium balance of your food do the heavy lifting, and flavanols sit at the margin. If you are managing persistent pain, the same applies: diet supports whatever else you are doing, and a supplement aimed at persistent back pain belongs alongside movement and a proper assessment, not instead of them.
Frequently asked questions
What is the highest source of flavanols?
Non-alkalised cocoa powder, by concentration. Per portion actually consumed, tea usually contributes most in a British diet, followed by apples, dark chocolate and red grapes. Processing changes the figure more than the raw ingredient does.
What do flavanols do?
Their best documented action is on the endothelium, the lining of your blood vessels, where their metabolites increase nitric oxide availability and the vessel widens. That is the basis of the only authorised claim in Great Britain and of most of the blood pressure evidence.
What drinks are high in flavanols?
Green tea, black tea and cocoa made with non-alkalised powder. Red wine contains catechins and procyanidins from the skins and pips, though the alcohol comes with its own costs. Coffee is high in polyphenols but they are chlorogenic acids, not flavanols.
Are flavanols the same as flavonols?
No. Flavanols are flavan-3-ols: catechin, epicatechin and procyanidins. Flavonols are quercetin, kaempferol and myricetin. Both belong to the flavonoid family, which is why the words get swapped, but the evidence behind them is separate.
How many milligrams of flavanols should I have a day?
An expert panel writing under the Academy of Nutrition and Dietetics process put the useful range at 400 to 600 mg a day of flavan-3-ols, from food, based on 157 randomised trials and 15 cohort studies. They specifically declined to recommend supplements.
Do cocoa flavanol supplements prevent heart disease?
The largest trial says not proven. COSMOS gave 21 442 older adults 500 mg of cocoa flavanols a day or placebo, and the primary cardiovascular endpoint came out at a hazard ratio of 0.90 with a P value of 0.11. Cardiovascular death, a secondary endpoint, did fall by 27 per cent, which is a reason for another trial rather than a conclusion.
Does milk in tea block flavanols?
Milk proteins bind flavanols in the cup, which is why tea with milk tastes less astringent. Studies of whether that reduces absorption have disagreed, and the radiolabelled work shows monomer absorption is high regardless. Drink it the way you will actually keep drinking it.
Sources
Crowe-White K.M., Evans L.W., Kuhnle G.G.C., et al. Flavan-3-ols and cardiometabolic health: first ever dietary bioactive guideline. Advances in Nutrition, 2022. DOI: 10.1093/advances/nmac105
Sesso H.D., Manson J.E., Aragaki A.K., et al. Effect of cocoa flavanol supplementation for the prevention of cardiovascular disease events: the Cocoa Supplement and Multivitamin Outcomes Study (COSMOS) randomized clinical trial. American Journal of Clinical Nutrition, 2022. DOI: 10.1093/ajcn/nqac055
Ottaviani J.I., Borges G., Momma T.Y., et al. The metabolome of [2-14C](-)-epicatechin in humans: implications for the assessment of efficacy, safety and mechanisms of action of polyphenolic bioactives. Scientific Reports, 2016. DOI: 10.1038/srep29034
Bondonno N.P., Dalgaard F., Kyro C., et al. Flavonoid intake is associated with lower mortality in the Danish Diet Cancer and Health Cohort. Nature Communications, 2019. DOI: 10.1038/s41467-019-11622-x
EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the substantiation of a health claim related to cocoa flavanols and maintenance of normal endothelium-dependent vasodilation. EFSA Journal, 2012. DOI: 10.2903/j.efsa.2012.2809
Del Rio D., Rodriguez-Mateos A., Spencer J.P.E., Tognolini M., Borges G., Crozier A. Dietary (poly)phenolics in human health: structures, bioavailability, and evidence of protective effects against chronic diseases. Antioxidants and Redox Signaling, 2013. DOI: 10.1089/ars.2012.4581
This article is general information, not medical advice. Speak to a pharmacist or your GP before starting a supplement, particularly if you take prescribed medication for blood pressure.
