According to the August issue of Mayo Clinic Women's HealthSource, these benefits are derived from flavonoids in dark chocolate.
Flavonoids are a naturally occurring antioxidant that are also found in teas, red wine and some fruits and vegetables.
The flavonoids in dark chocolate have been associated with a beneficial effect on the cardiovascular system.
One recent study showed that 6 grams of dark chocolate a day, about one square, lowered systolic and diastolic blood pressure by 2 points each.
Dark chocolate also may lower low-density lipoprotein (LDL) cholesterol levels by about 5 points. While not a huge affect, it's sending that "bad" cholesterol in the right direction.
Also, flavonoids have a beneficial effect on how the lining of the blood vessels function.
"We think a lot of bad things that happen to the cardiovascular system are because the lining of the vessels cracks and becomes inflamed, setting the stage for plaques to form and rupture," says Robert Sheeler, M.D., a family physician at Mayo Clinic.
To gain the health benefits, there's no need to eat a whole chocolate bar. After all, chocolate still contains calories and fat.
Dr. Sheeler says just one square a day, about 30 calories worth, will provide the health benefits.
Generally, to gain health benefits, Dr. Sheeler recommends chocolate that contains at least 60 percent cocoa. Milk chocolate typically has 15 percent to 25 percent cocoa.