The Kuna Indians, inhabitants of a remote island in Panama, have almost no instances of high blood pressure, stroke, or heart disease. Their secret? It could be chocolate, says a team of scientists led by Norman K. Hollenberg, MD, PhD, professor of radiology at Brigham and Women’s Hospital in Boston, who has been studying the tribe for decades. The team first thought genetic factors explained the Kunas’ low susceptibility to stroke and heart disease, but when tribespeople migrated to cities in mainland Panama, their rates of these diseases increased.
Digging deeper, the researchers noted that the islanders ate four times as much fish, twice as many fruits, and 10 times the amount of cocoa as the general population. They drank at least four cups of a mix of sugar, water, and strong cocoa daily.
The team’s findings, published in various periodicals, including the International Journal of Medical Sciencesand the Journal of the American Society of Hypertension, have spurred interest in the health benefits of chocolate, says Farzaneh H. Sorond, MD, PhD, professor of neurology at Northwestern University Feinberg School of Medicine in Chicago. “Data on the Kuna Indians are one of the most significant pieces of epidemiologic research on chocolate,” she says.
Since then, most studies have looked at chocolate’s effect on stroke. One of the earliest and largest was a Swedish study published in Neurology in 2012. After tracking 37,103 men for 10 years, researchers found that those who ate about 2 ounces of chocolate a week had a lower risk of stroke than those who didn’t eat chocolate. An even larger study, published in Atherosclerosis in 2017, looked at the dietary habits of 85,000 men and women in Japan over 12 years and found that women who ate chocolate—1.3 ounces a day—had a lower risk of stroke than women who ate no chocolate. No such benefit was found among men. Just last year, a meta-analysis of 16 studies published in Nutritionreported that chocolate eaters had a lower risk of stroke.
Researchers believe that flavonoids, a compound found in cocoa beans as well as fruits, vegetables, and other plant-based foods, may play a neuroprotective role. “In our lab, we’re looking at types of flavonoids called flavanols. Cocoa contains more flavanols than any other food on a per-weight basis. Flavanols protect the brain, heart, and other organs in multiple ways,” says Giulio Maria Pasinetti, MD, PhD, endowed professor of neurology at the Icahn School of Medicine in New York, who has conducted animal studies on the effects of cocoa flavanols on amyloid plaque, a hallmark of Alzheimer’s disease.
A small study published in Nature Neuroscience in 2014 looked at the effect of cocoa flavanols on the dentate gyrus, a region of the brain’s hippocampus that shrinks with age and is involved in memory. The study, partially funded by Mars, Inc., found that participants who supplemented their diet with a drink high in cocoa flavanols performed better on tests of pattern recognition and memory than a control group that drank a low-flavanol beverage. In addition, functional MRI scans of those who drank the high-flavanol beverages showed improved blood flow to the dentate gyrus compared with those who did not supplement their diet.
But flavanols might be just the beginning of the story, says Dr. Sorond. “Flavanols are promising because their antioxidant and anti-inflammatory effects may help protect blood vessels and brain cells, but research indicates other constituents in chocolate may be at play,” she says.
In her own study, published in Neurology in 2013, Dr. Sorond followed 60 men and women ages 67 to 78 who drank two cups of an unsweetened cocoa beverage daily for a month. Half the group drank a low-flavanol beverage; the other, a high-flavanol drink (supplied by Mars, Inc.). They consumed no other form of chocolate during the study.
The low- and high-flavanol drinks appeared to work equally well, but for just 17 of the participants, all of whom had impaired brain blood flow response. By the study’s end, this subgroup showed an 8 percent improvement in blood flow response. They also performed better on tests measuring working memory and speed of processing information. (For those with normal blood flow to the brain, the chocolate beverages didn’t cause any changes.)
Why would a low-flavanol drink help? “It could be that cocoa flavanols are effective even at low doses, or that something else in cocoa leads to brain improvements,” says Dr. Sorond. “At this point, we don’t know all the constituents in cocoa that are protective.”
Dr. Sorond hopes the recently launched Cocoa Supplement and Multivitamin Outcomes Study (COSMOS) by researchers at Brigham and Women’s Hospital in Boston and Fred Hutchinson Cancer Research Center in Seattle adds clarity. For the next four years, 22,000 people across the United States will take a pill containing 600 mg of cocoa flavanols and/or a multivitamin/mineral tablet. Researchers will look at the effects of the supplements on the risk of health conditions including stroke, poor memory, heart disease, and cancer.
While some research has suggested chocolate may be good for brain health, experts advise caution. “These studies are important for generating theories, but only controlled, rigorous randomized trials on animals and humans will tell us the extent of chocolate’s benefits,” says Joshua Z. Willey, MD, FAAN, assistant professor of neurology at Columbia University College of Physicians and Surgeons in New York.
In the meantime, Dr. Willey says, following a healthy diet and exercising are still top priorities for cardiovascular and brain health. “But eating truly dark chocolate in moderation could offer a health edge.”
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