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The idea that eating cocoa-rich, dark chocolate may offer greater health benefits than milk chocolate is not new. Cocoa is loaded with compounds called polyphenols that have been shown to help our bodies fend off inflammation and maybe even improve our moods, according to The Salt blog from the NPR Science Desk.

And now a small study published in the Journal of the American Heart Association offers evidence of another possible benefit: improving vascular health by increasing blood flow.

Researchers studied patients with peripheral artery disease, or PAD, which affects about 20 percent of adults older than 70 in the U.S. and other Western countries. People who have PAD can have trouble walking and exercising since blood flow to their limbs becomes impaired. Cramping can be a problem, too.

As part of the study, researchers gave half of the 20 participants 40 grams (about 1.5 ounces) of dark chocolate that had at least 85 percent cocoa. The other half of the group received 40 grams of milk chocolate that had less than 30 percent cocoa. The aim was to test whether the dark chocolate could improve those patients' ability to walk on their own on a treadmill.

"After eating the dark chocolate, [the participants] walked an average 11 percent farther," study author Lorenzo Loffredo of Sapienza University of Rome tells The Salt in an email. And yes, he says they were surprised by the findings.

He and his colleagues observed improved blood flow among the participants who ate the dark chocolate. "Conversely, we did not observe effects on blood flow and on walking autonomy in PAD patients after milk chocolate consumption."

So what explains the link between dark chocolate and improved walking?

The researchers say the polyphenols in dark chocolate can help reduce oxidative stress and help the body form more nitric oxide, a compound that causes blood vessels to dilate.