Dark chocolate is a type of chocolate that contains a high proportion of cocoa solids (at least 35%) and very little, if any, milk (no more than 12%). It can be found in sweet (35-45% cocoa solids), semi-sweet (40-62% cocoa solids), bittersweet (60-85% cocoa solids), and unsweetened varieties (100% cocoa solids, usually about half of it fat – cocoa butter). The high proportion of cocoa in this chocolate bestows the treat with some of the healthier properties attributed to the cacao bean.
In August 2005, research from Dr Denise O’Shaugnessy’s group in Southampton England showed that cocoa can help prevent clot formation, which potentially affects heart disease and stroke rates. The flavinoids found in cocoa, similar to those found in red wine, prevent platelet function. Platelets are small cells in the blood that bind to one another’s “sticky” surfaces to close wounds via the clotting processes. Platelet clotting within the blood vessels causes obstructions, cutting off the blood supply to the downstream tissue. In the presence of other disease factors, increased platelet function can exacerbate coronary artery disease and block the cerebral arteries, leading to heart attack or stroke, respectively.
Flavanols are a class of flavonoids that include the catechins. They are also known as flavan-3-ols (or flavanoids) and are well known antioxidants thought to relax blood vessels. They are found in a number of foods, including red wine and green tea. The USDA has a database of the flavanoid content of foods.
In 2006, a Dutch team found that elderly men who drank cocoa had lower blood pressure, which was tied to the flavan-3-ols in the chocolate precursor. At that time, the suggested therapeutic amount of raw cocoa would be intolerable for most people because of the bitterness, making it necessary to consume 100 g per day of dark chocolate to obtain the necessary flavanoids to have a therapeutic effect (500 calories, 30% fat)! It appeared that eating or drinking chocolate to improve heart health was unreasonable.
However, by 2007, many researchers had found supporting evidence for the benefit of flavanol-rich cocoa in regards to increasing blood flow in the brain. The research was encouraged by Mars, Incorporated, a worldwide chocolate bar maker and distributor who released a flavanol-rich chocolate bar in 2003, but much of the evidence has come from academic laboratories as well. One study from the University of Nottingham Medical School in the United Kingdom found that consuming a cup of the enriched cocoa results in increased blood flow in the brain for 2 to 3 hours.
Another group working out of Harvard Medical School studied the Kuna Indians of Panama, a tribal community that daily consumes a flavanol-rich cocoa. The population has low rates of cardiovascular disease and hypertension, and was also found to have lower cancer rates than their non-indigenous counterparts in Panama.
In May 2010, researchers from Johns Hopkins University School of Medicine published research indicating the mechanism by which cocoa triggers protective pathways in the brain vascular network. The flavanol of interest is epicatechin. When mice were given epicatechin 90 minutes before a stroke, the damage caused by the stroke was minimized, meaning that more blood got through than likely would have. If given after a stroke, a benefit was seen for 3 hours, but not for 6 hours. Does this mean cocoa may be used to treat strokes? Not likely, definitely not in the near future according to Dr. Dore who led the Johns Hopkins group because it has only been validated in mice and much more research is needed to understand the mechanism.
Though dark chocolate can be a palatable means of obtaining the cocoa and its flavanols, cocoa is a healthier means altogether. Even that though may contain more calories than it is worth.
See CacaoWeb for more information on the types of chocolate.
Some information taken from ScienceDaily, International Journal of Medical Sciences, BBC, and YahooNews.