Eating dark chocolate - a food rich in polyphenols - may help people with peripheral artery disease walk a little longer and farther before pain sets in, scientists have found.

In a small study, people with artery problems in their legs walked a little longer and farther when they ate dark chocolate.

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 the 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 per cent, making it rich in polyphenols. The milk chocolate, with a cocoa content below 30 per cent, had far fewer polyphenols.

After eating the dark chocolate, they walked an average 11 per cent farther and 15 per cent longer (almost 12 metres 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, but the benefit of dark chocolate polyphenols is "of potential relevance for the quality of life of these patients," said Lorenzo Loffredo, 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, study senior author and professor of internal medicine at the Sapienza University.

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 research was published in Journal of the American Heart Association.