The COSMOS-Mind (COcoa Supplement and Multivitamin Outcomes Study of the Mind) study, which was published in PNAS, involved more than 3,560 older adults randomly assigned to a three-year intervention of cocoa extract (500 mg of cocoa flavanols per day) or placebo.
The researchers claim their findings show that habitual flavanol consumption and diet quality are “positively and selectively correlated” with hippocampal-dependent memory
Flavanol consumption linked with lower risk of chronic disease
Dietary flavanols – bioactive compounds commonly found in fruits and vegetables such as tea, apples, berries, grapes, and cocoa – have been linked with a decreased risk of developing chronic diseases, such as cardiovascular disease, metabolic disorders, and cancer. They have also been linked to cognitive ageing, specifically with hippocampal-dependent memory.
Previous studies indicate that the memory benefits of an intervention with flavanols might depend on habitual diet quality; however, findings have been mixed. While some research suggests that people with a low intake of flavanols have a higher risk of heart disease, a separate COSMOS-Mind study found that cocoa extract had no effect on cognitive function.
The authors of the PNAS study, which was partially funded by confectionery multinational Mars, used the alternative Healthy Eating Index in all participants and a urine-based biomarker of flavanol intake in a subset of participants to test their hypothesis.
They said their results suggest that low flavanol consumption can act as a driver of the hippocampal-dependent component of cognitive ageing.
Findings ‘do not support the claim that flavanols improve memory function’
However, critics questioned whether the study provided the evidence as claimed, highlighting the authors’ admission that “the prespecified primary end point testing for an intervention-related improvement in memory in all participants after one year was not statistically significant”.
Professor David Curtis, honorary professor at UCL’s Genetics Institute, said: “I’m afraid that the results obtained do not support the claim that flavanols improve memory function. Even in the group who initially had low flavanol consumption, those taking a flavanol supplement for years had about the same memory function as those taking placebo and any differences were well within chance expectation.
“The authors do claim that a couple of results are statistically significant but in my view this because the analyses have been performed incorrectly. If anything, this study shows that flavanol supplements do not have any major effect on memory function.”
Meanwhile Naveed Sattar, professor of metabolic medicine at the University of Glasgow, said: “It is great to see a randomised trial in this space with decent numbers. The key result is, in fact, the trial result, which was clearly negative at all three years. In other words, there is no evidence that a diet rich in flavanols protects from memory loss.
“The rest of the paper is observational and creates the illusion of benefit, but it is of little value.”
Results ‘emphasise the role of nutrition in the maintenance of the ageing brain’
Others sounded a more cautious note.
Dr Ian Johnson, emeritus fellow at the Quadram Institute in Norwich, pointed out that the study was “large and rigorously conducted”, adding: “These results emphasise the role of nutrition in the maintenance of the ageing brain, and in particular they suggest the importance of maintaining a high-quality diet, rich in everyday sources of flavanols such as apples, grapes, other berries, and tea.
“In circumstances where this is difficult, the use of dietary supplements may be a practical solution.”
As flavanol-rich plants contain these compounds in different combinations and quantities, they can have different health effects, and so it is recommended that the best way to consume enough of them is by eating a variety of fruits and vegetables.
The European Food Safety Authority (EFSA) has approved one health claim for cocoa flavanols – namely, that they “help maintain endothelium-dependent vasodilation, which contributes to normal blood flow”.
It adds: “To obtain the claimed effect, 200 mg of cocoa flavanols should be consumed daily.