That depends on the cocoa, which is just chocolate minus its natural fat (cocoa butter). Most commercially available cocoa products have been so processed that they end up providing few, if any flavanols, the heart healthy components of raw cocoa beans. A comparison of the flavanol content of various chocolate products, published in the August 2005 Journal of Hypertension, by distinguished researchers Norman K. Hollenberg, M.D., Ph.D. of Harvard Medical School and Naomi D. Fisher M.D. of Brigham and Women's Hospital, found that the product providing the most flavanols - nearly 5,000 mg per 100 grams of cocoa - was CocoaPro powder developed by the chocolate manufacturer Mars Inc. In second place was cocoa powder made by the Kuna Islanders of Panama, who drink an average of five cups of cocoa per day and have very low rates of high blood pressure, heart disease and cancer. The researchers reported that the flavanol content of "all of the commercially available cocoa powders or chocolate drinks" on U.S. supermarket shelves are substantially less than that of CocoaPro.
If you want to continue using cocoa in your coffee, I suggest looking for products that haven't undergone Dutch processing - that is, they haven't been treated with an alkali to neutralize cocoa's natural acidity. But even then you can't be certain that you're getting much in the way of the beneficial flavanols.
Although not as popular as coffee, drinking hot chocolate made from unsweetened dark chocolate may have significant health benefits. Researchers at Harvard Medical School analyzed 21 studies that involved more than 2,500 participants and found that drinking chocolate is associated with reduced blood pressure, improved blood vessel health and lowering LDL ("bad") cholesterol and elevating HDL ("good") cholesterol. They presented their findings at the American Heart Association's Nutrition, Physical Activity and Metabolism/Cardiovascular Disease Epidemiology and Prevention 2011 Scientific Sessions.
Earlier evidence suggested that drinking cocoa may be responsible for the very low incidence of heart disease, stroke, diabetes and cancer among the Kuna Islanders. The cocoa they drink is made from gently processed home-grown cacao beans. Otherwise their native diet is low in protein, very low in fat, rich in fruit and, surprisingly, high in salt. A few years ago Harvard's Dr. Hollenberg identified epicatechin, one of the cocoa flavanols, as the active ingredient responsible for the Kuna's good health.
My preferred way to get the health benefits chocolate has to offer is enjoying an ounce or two of dark chocolate that's 70 percent cocoa several times a week. You have no cause for concern about the fat in dark chocolate - it is stearic acid, a type of saturated fat that does not raise cholesterol levels. And chocolate that is 70 percent cocoa does not contain much sugar.
Andrew Weil, M.D.