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Cocoa flavanols

Antioxidant · Cocoa extract, cocoa flavanols, epicatechin

Cocoa flavanols bring more to the table than most plant compounds: a mode of action shown in humans, an authorized EU health claim and a large endpoint trial. In COSMOS, with 21,442 older adults, there were 27 percent fewer cardiovascular deaths. The primary endpoint was narrowly missed, and overall there was no effect on cognitive performance.

What cocoa flavanols are

Cocoa flavanols are flavan-3-ols from the cocoa bean, a subgroup of polyphenols. The most important are epicatechin and catechin as well as procyanidins, short chains made of these building blocks. They are found in cocoa powder and dark chocolate and are offered as standardized cocoa extract in capsules and tablets; in the studies of the Cochrane analysis, the amounts ranged from 30 to 1,218 mg a day.

In the BK-Score, human evidence stands at 7 out of 10 points, carried mainly by the COSMOS trial. Related polyphenols are EGCG from green tea, quercetin and resveratrol; nitrate from beetroot also works via nitric oxide. The page Heart and blood pressure gives an overview.

How it works

In 2006, Schroeter and colleagues showed in healthy men that flavanol-rich cocoa raises the concentration of nitric oxide compounds in the blood and improves the flow-mediated dilation of large arteries. They identified epicatechin as the active compound: pure epicatechin mimicked the effect, and in vascular preparations it disappeared when nitric oxide formation was blocked.

In 2012, the European Food Safety Authority EFSA saw a causal relationship between cocoa flavanols and endothelium-dependent vasodilation. How this could translate into fewer deaths has not been clarified. One clue comes from a COSMOS substudy in which the inflammatory marker hsCRP rose more slowly under cocoa extract.

What is well supported

  • Fewer cardiovascular deaths in a large trial. In COSMOS, cardiovascular mortality fell by 27 percent; in participants who took their capsules regularly, the number of all cardiovascular events fell as well.
  • Better vascular function, officially recognized. The mode of action via nitric oxide has been shown in humans. Since 2013, the EU has allowed the claim that cocoa flavanols help maintain the elasticity of blood vessels, and since 2015 also for capsules and tablets with cocoa extract.
  • Slightly lower blood pressure. A Cochrane review of 35 studies found on average 1.76 mmHg less, both systolic and diastolic.
  • Slowed inflammation in old age. In a substudy with 598 participants, hsCRP rose by 8.4 percent less per year under cocoa extract than under placebo.
  • No safety concerns over years. COSMOS found none in more than 21,000 people over a median of 3.6 years.

What the studies show

Sesso 2022: COSMOS and cardiovascular disease

COSMOS is a double-blind, placebo-controlled trial with 21,442 Americans, women aged 65 and over and men aged 60 and over, without known cardiovascular disease. Half received a cocoa extract with 500 mg of flavanols a day, including 80 mg of epicatechin. After a median of 3.6 years, 410 participants under cocoa extract and 456 under placebo had a cardiovascular event, HR 0.90 (0.78 to 1.02; p = 0.11). The primary endpoint was thus narrowly missed. Among the secondary endpoints, cardiovascular mortality fell by 27 percent (HR 0.73; 0.54 to 0.98); in the per-protocol analysis, which excludes periods without regular intake, total events were also lower (HR 0.85; 0.72 to 0.99).

Li 2025: inflammaging

In a random sample of 598 COSMOS participants, with an average age of 70, five inflammatory markers were measured at baseline, after one year and after two years. Under cocoa extract, hsCRP rose by 8.4 percent less per year than under placebo (−14.1 to −2.3 percent), also after correction for multiple testing. Interferon-gamma rose by 6.8 percent; the other markers did not change.

Ried 2017: blood pressure in the Cochrane review

The review covered 35 randomized trials with 40 comparisons and 1,804 mostly healthy participants over two to 18 weeks. Compared with low-flavanol or flavanol-free controls, flavanol-rich cocoa products lowered systolic blood pressure by 1.76 mmHg (−3.09 to −0.43) and diastolic blood pressure by 1.76 mmHg (−2.57 to −0.94).

COSMOS-Mind, COSMOS-Clinic and COSMOS-Web: cognitive performance

In COSMOS-Mind, 2,262 participants with an average age of 73 were tested by telephone once a year for three years: cocoa extract did not change global cognition (Baker 2023). The 573 participants of the clinic subgroup underwent detailed on-site testing; here too, there was no effect after two years (Vyas 2024). In COSMOS-Web, with 3,562 participants, memory missed the primary endpoint after one year, but it improved in participants with poor diet quality or low everyday flavanol intake (Brickman 2023).

Where the data stop

  • The primary endpoint. All cardiovascular events combined did not fall significantly in COSMOS. The 27 percent fewer deaths are a secondary endpoint and need confirmation, as the authors themselves say. In absolute terms, events were 410 versus 456 in groups of around 10,700 people each; more on this under relative and absolute risk reduction.
  • Brain and memory. Two large COSMOS substudies found no effect on cognition. The positive finding from COSMOS-Web concerns a subgroup with a poor diet, not everyone.
  • Biological age. After two years in 958 participants, the cocoa extract had no effect on five epigenetic aging clocks, unlike the multivitamin in the same trial.
  • Who was studied. COSMOS included only older adults without cardiovascular disease. The trial provides no data for younger people or for people with existing heart disease.
  • Chocolate as a substitute. The studies tested standardized extracts or defined cocoa products. Whether a particular chocolate delivers the study amount cannot be said without information on its flavanol content.

Status, approval and legal

Cocoa flavanols are marketable as a food ingredient and in food supplements. In 2012, EFSA confirmed a causal relationship between cocoa flavanols and endothelium-dependent vasodilation. With Regulation (EU) No 851/2013, the Commission authorized the claim “Cocoa flavanols help maintain the elasticity of blood vessels, which contributes to normal blood flow”, initially for cocoa beverages with cocoa powder and dark chocolate. Regulation (EU) 2015/539 extended it to capsules and tablets with flavanol-rich cocoa extract.

The conditions are narrow: the product must provide at least 200 mg of cocoa flavanols with a degree of polymerization of 1 to 10 daily, and consumers must be informed that the beneficial effect is obtained with this daily amount. The claim was authorized at the request of a cocoa processor, based on a study that the applicant described as proprietary; it was therefore initially restricted to that applicant for five years. It does not cover a healing claim, for example protection against heart attack.

Safety

In COSMOS, more than 10,000 people took 500 mg of cocoa flavanols daily over a median of 3.6 years without any safety concerns emerging. For a plant compound, this is an unusually broad database, although in older people without cardiovascular disease.

For pregnant women, children and people with heart disease, these studies provide no safety data. In the BK-Score, safety data stands at 7 out of 10: well studied, not harmless. This text is information and does not replace medical advice.

BK-Score Supported, with caveats

Human evidence7
Mechanism7
Safety data7
Hype gap5
Track record of use7

Evidence 7, because COSMOS provides a large double-blind endpoint trial in 21,442 older adults over a median of 3.6 years that narrowly missed its primary endpoint (HR 0.90, p = 0.11) but showed 27 percent fewer cardiovascular deaths (Sesso 2022), and a Cochrane review of 35 studies finds a small reduction in blood pressure (Ried 2017); on cognition, the large trials are negative (Baker 2023, Vyas 2024). Mechanism 7, because it has been shown in humans that epicatechin improves vasodilation via nitric oxide (Schroeter 2006), and EFSA recognizes this relationship as causal; how this translates into fewer deaths is open, one clue being the slowed rise in hsCRP (Li 2025). Safety 7, because COSMOS found no safety concerns over years in more than 21,000 people, but the participants were older and without cardiovascular disease. Hype 5, because the vascular effect holds up, but cocoa is additionally promoted as a brain and anti-aging remedy, although cognition in the overall group and the epigenetic aging clocks remained unchanged (Li 2026). Use 7, because cocoa has been eaten for centuries and since 2015 the EU has also allowed flavanol-rich cocoa extract with a health claim as a capsule or tablet, but experience with high-dose extracts comes mainly from studies. Direction mixed: blood vessels and cardiovascular mortality speak in favor, the primary endpoint and cognition do not.

The score rates the state of knowledge, not the substance. “Safety data 7” means well studied – not harmless. “Track record of use 7” means used long and widely – that is not proof of efficacy.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)

Frequently asked questions about cocoa flavanols

What does the COSMOS trial show on cocoa flavanols?

COSMOS gave 21,442 older Americans 500 mg of cocoa flavanols or placebo daily for a median of 3.6 years. The primary endpoint, all cardiovascular events combined, was narrowly missed (HR 0.90; p = 0.11). Cardiovascular deaths fell by 27 percent; that is a secondary endpoint. No safety concerns arose.

Do cocoa flavanols lower blood pressure?

Slightly. A Cochrane review of 35 studies with 1,804 mostly healthy participants found on average 1.76 mmHg less, both systolic and diastolic. The studies ran for two to 18 weeks. This effect is not enough to treat high blood pressure.

Do cocoa flavanols improve memory?

Not in the overall group. COSMOS-Mind with 2,262 participants over three years and the clinic subgroup with 573 participants tested in detail found no effect on cognition. In COSMOS-Web, memory improved only in participants with poor diet quality or low everyday flavanol intake.

Is dark chocolate enough?

That can only be answered with information on the flavanol content. The EU health claim applies only to cocoa beverages, dark chocolate or capsules and tablets that provide at least 200 mg of cocoa flavanols daily. COSMOS tested a standardized extract with 500 mg of flavanols, not chocolate.

Do cocoa flavanols slow aging?

Evidence for this is lacking. In a COSMOS substudy with 958 participants, cocoa extract did not change five epigenetic aging clocks after two years. Another substudy found a slower rise in the inflammatory marker hsCRP; that is a laboratory value and not a measure of aging.

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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-11-07.