Research shows flavanols have potential cardiovascular benefits which include lowering blood pressure and improving blood flow possibly reducing the risk of cardiovascular disease. The research is not concrete but some studies also show improved insulin sensitivity in diabetics and short term increase in blood flow to the brain improving alertness and performance. One study even found people who consumed flavanol rich chocolate, wine, or tea scored higher on cognitive tests than those who did not.
Cocoa beans undergo processing to turn into chocolate. The more processed the chocolate is, the less flavanols it contains. Milk also interferes with the antioxidants found in chocolate and can block the potential health benefits. Added fat and sugar also reduce the health benefits of chocolate changing it from a "superfood" into a junk food.
Look for chocolate that contains at least 70% cocoa and keep your serving size to 1.4-2 ounces daily. Cocoa is very bitter and pungent in taste. Switching from a sugary milk chocolate bar to 70% dark chocolate may be a shock for your taste buds. Some find dark chocolate to be an acquired taste that takes some time to get used to. Start small and eat it with things you enjoy. My guilt free treat is drizzling some melted 72% cocoa over a handful of raspberries. However you choose to enjoy your dark chocolate, know the biggest reward is the impact on your health.