Cocoa flavanols may boost memory, but don't start buying chocolate

If your diet is low in flavanols — antioxidant compounds found in foods such as green tea, apples, berries, and cocoa — adding 500 milligrams a day to your diet may slow and possibly improve age-related mental decline, according to a new study.

Age-related mental decline is typically subtle. The condition impacts thinking speed and the ability to sustain attention and causes issues with word-finding, and it should not be confused with Alzheimer's disease and other dementias, experts say.

"Older adults consuming lower levels of food-borne flavanols scored less well in tests of hippocampal memory function than individuals consuming higher levels," said Dr. Ian Johnson, emeritus fellow at the Quadram Institute in Norwich, a center for food and health research in the United Kingdom. He was not involved with the study. The hippocampus is a part of the brain that regulates learning, spatial navigation, and storage and consolidation of memory.

When those same people were given daily supplements with flavanols derived from cocoa, however, their performance on an age-related word-recall test improved, Johnson said in a statement. He was not involved in the study, which was published Monday in the journal PNAS Neuroscience.

Still, any impact on memory was modest, "and limited to those individuals with a lower quality diet at the start of the study," said Dr. Davide Bruno, a reader in psychology at Liverpool John Moores University in the UK, in a statement. He was not involved in the study.

What are flavanols?

Flavanols, also called flavan-3-ols, are compounds that help give fruits and vegetables their bright colors. Each plant may contain more than one type of flavanol, as well as necessary micronutrients that complement each other. That's a key reason many nutritionists recommend "eating the rainbow" to get the most benefit.

All flavanols are bioactives, naturally occurring compounds that affect processes within the body. The Academy of Nutrition and Dietetics recommended in 2022 a daily intake of 400 to 600 milligrams of flavanols. The association cited studies that showed the compounds may reduce the risk of cardiovascular disease and diabetes.

Unlike carbohydrates, fats, proteins, vitamins, minerals, and water, flavanols are not necessary to survive. But much like fiber, they are critical for good health, said study coauthor Gunter Kuhnle, a professor of food and nutritional science at the University of Reading in the UK.

"Fiber is not essential for survival," he said, but "it's really important that people consume sufficient amounts of fiber to have good cardiovascular health and protect against cancer."

The study's findings about flavanols, Kuhnle said, may be "the first indication that exactly the same thing might be true here."

Eating chocolate won't work

Despite the fact that the study tested 500 milligrams of flavanols derived from cocoa, that does not mean you can get similar results from eating 500 milligrams of chocolate.

"What really doesn't contain a lot of flavonoids are chocolates," Kuhnle said.

In order for researchers to extract as many flavonoids from the dark cocoa as possible, the extraction process was intensely "optimized" in the lab, Kuhnle explained.

"The best way to meet 500 milligrams a day is by consuming a range of different flavanol-containing foods," he said.

Many foods do contain enough flavanols to meet that daily level, Kuhnle said, including berries, apples, grapes, nectarines, and pears. Green tea is an excellent source — but only if you drink it.

"This is really about green tea, not green tea extract," he stressed. "Extreme amounts of green tea extract (can) cause problems. People think, 'Oh, if I'm on x, that's fine, twice the amount of x is better, and 10 times is even better.'

"That's one reason to always be cautious about supplements: It's incredibly easy to increase amounts beyond what is sensible and beyond what is useful," Kuhnle said.

In addition, when it came to optimizing levels of flavanols, there was "no advantage in going above these 500 milligrams and it's achievable by diet, so there's not really any need to go to supplements," Kuhnle said.

Mixed opinions

The new research is a subsidiary of a much larger study of over 21,000 adults older than age 60 called the Cocoa Supplement and Multivitamin Outcomes Study, or COSMOS that was published in March 2022. Cocoa supplements and partial grant money was provided by Mars Edge, a segment of Mars Inc.

In the new study, 3,562 adults were divided into two groups — one cohort took a daily placebo, or sugar pill, for three years. The other took a daily 500-milligram pill packed with flavanols extracted from cocoa, including 80 milligrams of epicatechin, a flavonoid long studied for its positive effects on muscle strength and blood flow in the brain.

Over 1,300 of the study participants underwent urine tests at the start of the study to determine levels of flavanols in their system.

All participants underwent a baseline cognitive evaluation, in which they were asked to learn 20 words on a computer program. The research participants had three seconds to study each word before the next appeared. Immediately after, participants were asked to type all the words they could remember. The test was repeated every year for the length of the three-year study.

At the end of the first year, people in the study who took the daily 500-milligram pill and who had tested in the bottom tier of flavanols "normalized" their levels of flavanols, said study coauthor Dr. Scott Small, professor of neurology and director of the Alzheimer's Disease Research Center at Columbia University in New York City.

In those people, the flavanols also "restored" their age-related mental decline to levels similar to people who "had high flavanols at baseline," he said.

Some experts interpreted the study's findings differently.

"The study fails to provide evidence that increasing flavanol intake is beneficial," said David Curtis, an honorary professor at the Genetics Institute at University College London who was not involved in the study.

"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," Curtis said in a statement.

Study data showed that by year three people who had the lowest levels of flavanols at the start of the study and then took the cocoa supplement remembered 7.94 words out of 20, compared with 7.63 in the placebo group, a difference of about a fourth of a word.

That small difference was not significant, said Dr. Jeffrey Linder, chief of general internal medicine at Northwestern University's Feinberg School of Medicine in Chicago.

"Within the low diet quality group, there was a significant trend in increasing word recall in the flavanol group relative to the placebo group, but there were no individual year significant differences," said Linder, who was not involved in the study.

In fact, the majority of the study participants did not show any statistically significant benefits in memory from taking the cocoa supplement, meaning the trial "failed" to achieve its intended result, said Tara Spires-Jones, professor of neurodegeneration and deputy director of the Centre for Discovery Brain Sciences at the University of Edinburgh in Scotland, who was not involved with the research.

"In other words, there is NO evidence that a diet rich in flavanols protects from memory loss," said Naveed Sattar, a professor of cardiovascular and metabolic health at the University of Glasgow in Scotland, in a statement.

"People should not rush to such drinks or diets but rather keep doing the things that we 100% know protect against many illnesses — eat better (and fewer calories if overweight), walk a little more and sleep well, and have traditional risk factors tested and, if needed, improved," said Sattar, who was not involved in the study.

Research into flavanols

Small, the neurologist at Columbia University, has studied flavanols for years and coauthored a 2014 study that looked at brain scans of 37 healthy volunteers who took 900 milligrams of cocoa flavanols for three months. He and his colleagues found increased blood flow in the dentate gyrus, a part of the hippocampus complex in the brain, as well as a significant improvement in memory.

"These dietary flavanols … just sort of boost up memory," Small said. "It seems to focus on hippocampal-dependent memory. The hippocampus is a system that's like the 'click save' function on our computers."

Small and his colleagues repeated the analysis on 211 people between the ages of 50 and 74 who took various levels of cocoa extract flavonoids for three months. People who took the highest levels of flavanols improved their performance on one of three tests of cognitive function, according to the February 2021 study. However, brain scans of a subset of the group found no direct increase in blood flow to the hippocampal region.

In both studies, cocoa supplements were provided by Mars Edge.

Other researchers have also found flavanols have a cognitive benefit, albeit small. A February study found cognitive scores of people who ate the most flavanols declined more slowly per decade than those who ate the fewest — but the difference was very small.

A November 2020 study investigated why and found cocoa flavanols appear to increase blood flow to the cerebral cortex, the part of the brain responsible for decision making

"We do not yet know for sure whether flavanols specifically influence the risk of conditions like dementia," said Dr. Rosa Sancho, head of research at Alzheimer's Research UK at Cambridge, in a statement.

"We do know that things like staying mentally sharp, keeping socially connected, and keeping our heart healthy — including by eating a balanced diet — are important for looking after our long-term brain health," said Sancho, who was not involved in the study.