Well it really depends on what type of chocolate we are talking about... So here it is:
The benefits of chocolate were first recognised in The Kuna Indians. Studies have shown that The Kuna people in Panama routinely drank 3 cups of traditional cocoa a day and had lower blood pressure and heart attack rates, amongst other conditions. This sparked more research into the benefits of chocolate.
Further studies have shown that chocolate and cocoa drinks can improve blood pressure, cholesterol quality and the health of blood vessels.
But heres the catch... these studies have been conducted using specifically designed chocolate for research and not using the same chocolate that you can buy in the supermarkets.
The beneficial compounds in chocolate are polyphenols and more specifically epicatechin. However only small amounts of these compounds are found in supermarket bought chocolate.
So the key is to...look for 'bitter solids' on the label not cocoa solids as the latter includes butter and solids, as an indicator for potential health benefits. 15-20g/day of dark chocolate for enjoyment isn't a bad idea and will meet Public Health Englands recommendation for a new energy limit for the maximum of two 100kcal snacks a day.
EU. Eu Directive 2000/36/EC of the European Parliament and of the Council of the 23rd June 2000 relating to cocoa and chocolate products intended for human consumption. Off. J EUR Communities. 2000; L197:19-25.
Hollenberg NK, Fisher ND, McCullough ML. Flavanols, the Kuna, cocoa consumption, and nitric oxide. J Am Soc Hypertens. 2009;3(2):105–112. doi:10.1016/j.jash.2008.11.001