Cocoa polyphenols and blood vessel health, reviewed
What it found
Cocoa polyphenols have been linked to better blood vessel function and small drops in blood pressure in people, but many human studies were small and not placebo-controlled.
In lab and animal studies, the amounts used were often far higher than levels reached in human blood.
What they found
Studies in people
Absorption in people
After people drank cocoa-rich beverages or ate chocolate, cocoa polyphenols appeared in their plasma at low levels, often in the nanomolar or low micromolar range. Peak levels were seen 2 to 3 hours after eating.
Blood pressure in people
Some human studies found that cocoa polyphenols lowered systolic and diastolic blood pressure, with the effect more evident in people with high blood pressure. The size of the drop was often relatively low, and other studies found no benefit.
Blood vessel function
Cocoa polyphenols improved endothelial function in some human studies by increasing vascular nitric oxide synthase activity. But in people with coronary artery disease, flavonol-rich cocoa did not change vascular function over 6 weeks.
Chocolate calories
In one study, 100 g of dark chocolate daily for two weeks added 480 kcal per day and lowered systolic blood pressure by 5 mm Hg. The authors note that over time these extra calories would probably increase body weight and may work against any benefit for blood vessels.
Animal and lab studies
Lab and cell studies
In lab tests and cultured cells, cocoa polyphenols showed antioxidant and anti-inflammatory activity and affected several molecular targets. But the concentrations used in many cell studies are not achievable in the body.
Animal studies
In rabbits, hamsters, rats and mice, cocoa polyphenols reduced LDL oxidation, changed cholesterol levels, and in some cases lowered blood glucose. Some rat studies found no effect on markers of lipid peroxidation in liver and heart.
What the authors conclude
“In order to determine potential health benefits of cocoa polyphenols large scale, long term, randomized, placebo controlled studies, (ideally with a cross-over design) as well as prospective studies are warranted.”
Also in their conclusions
- They say that large scale, long term, randomised, placebo controlled studies, ideally with a cross-over design, are warranted to determine potential health benefits of cocoa polyphenols.
- They advise that products low in sugar and fat should be preferred, since chocolate is high in energy.
- They encourage the food industry to label the flavonoid content on cocoa derived products.
How it was done
The authors wanted to weigh up the evidence on cocoa polyphenols and blood vessel health, since cocoa is a rich source of these compounds and earlier lab work suggested possible benefits.
They reviewed studies from the last decade on cocoa polyphenols and vascular health, covering lab and cell studies, laboratory rodents, and human studies. They also looked at how cocoa polyphenols are absorbed and what levels appear in human plasma.
What it can’t tell you
- Many human studies were small, not placebo-controlled, and lacked rigorous design, so their results are hard to rely on.
- Lab and animal studies often used amounts of cocoa polyphenols that are not reached in the human body, so those findings may not apply to people.
- The products used in controlled studies often had much higher polyphenol levels than most commercially available products, so it is not clear whether everyday products have the same effects.
Who paid
- Authors work at
- Christian Albrechts University 24118 Kiel, Germany
The paper
- Title
- Polyphenols from cocoa and vascular health-a critical review
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Rimbach G, Melchin M, Moehring J, Wagner AE (2009). Polyphenols from cocoa and vascular health-a critical review. International journal of molecular sciences. doi:10.3390/ijms10104290Free full textPubMed 20057946DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error