In a small study, people with artery problems in their legs walked a little longer and farther when they ate dark chocolate – a food rich in polyphenols, according to new research in Journal of the American Heart Association.
Peripheral artery disease (PAD) is a narrowing of the peripheral arteries to the legs, stomach, arms, and head – most commonly in the arteries of the legs. Reduced blood flow can cause pain, cramping or fatigue in the legs or hips while walking.
In this pilot study of patients with PAD (14 men and six women, ages 60-78), study participants increased their ability to walk unassisted after eating dark chocolate, compared to when they ate milk chocolate. The authors suggest that compounds found in cocoa – polyphenols – may reduce oxidative stress and improve blood flow in peripheral arteries.
The patients were tested on a treadmill in the morning and again two hours after eating 40 grams of dark and milk chocolate (about the size of an average American plain chocolate bar) on separate days. The dark chocolate in the study had a cocoa content of more than 85 percent, making it rich in polyphenols. The milk chocolate, with a cocoa content below 30 percent, had far fewer polyphenols.
After eating the dark chocolate, they walked an average 11 percent farther and 15 percent longer (almost 12 meters/39 feet farther and about 17 seconds longer) than they could earlier that day. But distance and time didn't improve after eating milk chocolate.
The improvements were modest. Still, the benefit of dark chocolate polyphenols is "of potential relevance for the quality of life of these patients," said Lorenzo Loffredo, M.D., the study's co-author and assistant professor at the Sapienza University of Rome in Italy.
Levels of nitric oxide—a gas linked to improved blood flow—were higher when participants ate dark chocolate. Other biochemical signs of oxidative stress were also lower. Based on these observations and other laboratory experiments, the authors suggest that the higher nitric oxide levels may be responsible for dilating peripheral arteries and improving walking independence.
"Polyphenol-rich nutrients could represent a new therapeutic strategy to counteract cardiovascular complications," said, Francesco Violi, M.D., study senior author and professor of internal medicine at the Sapienza University of Rome.
The researchers said the improvements linked to these compounds in dark chocolate need to be confirmed in a larger study involving long-term consumption. The current study lacked a placebo group, and patients knew which kind of chocolate they were given, a factor that could influence the results.
American Heart Association spokesperson Dr. Mark Creager noted that it's far too early to recommend polyphenols or dark chocolate for cardiovascular health.
"Other investigations have shown that polyphenols including those in dark chocolate may improve blood vessel function. But this study is extremely preliminary and I think everyone needs to be cautious when interpreting the findings," said Creager, who is director of the Vascular Center at Brigham and Women's Hospital and a professor of medicine at Harvard Medical School in Boston.
"We know from other studies of antioxidants—vitamin C and vitamin E for example—that these interventions have not gone on to show improvement in cardiovascular health."
Chocolate adds calories to the diet. The American Heart Association recommends that men consume no more than 150 calories per day from added sugars (9 teaspoons) and women should consume no more than 100 calories (6 teaspoons) from added sugar per day and 5 percent -6 percent of calories from saturated fat. A typical American chocolate bar provides 94 calories from sugar (24 grams) and 8 grams of saturated fat.
Many other polyphenol-rich foods would offer less added sugar, saturated fats, and calories than dark chocolate, such as cloves, dried peppermint, celery seed, capers, and hazelnuts, to name a few.