Both arterial stiffness and white blood cell adhesion are known factors that play a significant role in atherosclerosis.  Diederik Esser, from Wageningen University (The Netherlands), and colleagues followed 44 middle-aged overweight men over two periods of four weeks as they consumed 70 grams of chocolate per day. Study participants received either specially produced dark chocolate with high flavanol content or chocolate that was regularly produced. Both chocolates had a similar cocoa mass content. Before and after both intervention periods, researchers performed a variety of measurements that are important indicators of vascular health.  The team observed that dark chocolate helped restore flexibility to arteries while also preventing white blood cells from sticking to the walls of blood vessels.  The study authors submit that: “chocolate affects endothelial health by … [improving] vascular function [and lowering] the adherence capacity of leukocytes in the circulation.”

From: http://www.worldhealth.net/news/dark-chocolate-deters-atherosclerosis/