In a small study, people with narrowed leg arteries walked a little farther, for a longer amount of time after eating dark chocolate, a food high in antioxidants called polyphenols, according to new research in Journal of the American Heart Association.

The authors suggest that polyphenols in cocoa may reduce oxidative stress and improve blood flow in peripheral arteries. Oxidative stress is an imbalance in the body that leads to inflammation, blood vessel damage and stiffening.

In the study, 14 men and six women, ages 60-78 who had peripheral artery disease improved their ability to walk unassisted after eating dark chocolate, but not after eating milk chocolate.

PAD is a narrowing of the arteries, most commonly in the legs. It can cause pain, cramping or fatigue in the legs or hips while walking.

Participants did treadmill tests in the morning, then later that day two hours after eating 40 grams of chocolate, about the size of an American chocolate bar. Tests for dark and milk chocolate were on separate days.

The dark chocolate was more than 85 percent cocoa, making it rich in polyphenols. The milk chocolate has less than 30 percent cocoa and far fewer polyphenols.

After eating dark chocolate, people walked 39 feet farther for about 17 more seconds on average than they did the same morning—improvements of 11 percent and 15 percent, respectively. Their distance and time didn’t improve after eating milk chocolate.

Despite modest improvements, 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, which researchers say may be responsible for dilating peripheral arteries and improving walking independence.

The researchers said the improvements linked to these compounds need to be confirmed in a larger study.

American Heart Association spokesperson Mark Creager, M.D. 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.”

Cloves, dried peppermint, celery seed, capers, and hazelnuts are other polyphenol-rich foods with less added sugar, saturated fats and calories than dark chocolate.