Mars Inc. - the company that has brought us M&M's or Snickers - sponsored 140 peer-reviewed scientific papers starting from the 80s. Mars controlled the research agenda and only funded the positive research, to push chocolate bars as nutritious. 

The biggest health claim is that cocoa lowers blood pressure, but no study has proven that it reduces the risk of heart disease or attacks. And considering the added sugars it probably does more harm than good.