When it comes to chocolate, can there be too much of a good thing? Much as a chocoholic like myself hates to admit it, the research seems to be pointing that way. It all started with a 2008 study that showed that healthy Italians who ate just one small serving, 20 grams, every three days had a substantial reduction in C-Reactive protein.  This is impressive as elevated C-Reactive protein levels are a leading indicator of Inflammation and inflammation is associated with an increased risk of heart disease, dementia, erectile dysfunction, autoimmune disorders and on and on.
This study said that dark chocolate, which is much more packed with cocoa than regular chocolate, is very powerful stuff and can provide therapeutic benefits even in small dosages. Notice that the ideal dosage in this study, 20 grams, is the equivalent of one square of chocolate from the tyical chocolate bar (at least here is the U.S.).
It also attacked the "more is better" philosophy of Americans like myself, where we tend to believe that if a little of some nutrient is good for us, then a lot must be really good. However, the researchers found that the reduction is C-reactive protein was significantly reduced in those who ate more.
One 2010 study (of middle aged and beyond women) showed a similar result: substantial protection against heart failure in those who ate just an ounce of chocolate - not necessarily dark in this case - once or twice per week.  Eating over one serving per day was associated in a loss of all protective benefits. Again, though, this study clearly showed that consuming too much chocolate may be pleasing the taste buds but eliminating the benefits.
So what would cause this phenomenon of diminishing and even reversing returns? Well, there are several possibilites. One is that cocoa is so powerful an antioxidant that the body actually stops producing its own. Or perhaps it alters an inflammatory metabolic pathway over a certain dosage. However, the most likely explanation in my opinion is that it is the milk in chocolate that causes the problem.
First of all, milk degrades the absorption of the chocolate's polyphenols responsible for its anti-inflammatory properties  and, most importantly, milk is actually pro-inflammatory in and of itself.  In fact, the same study summarizes that milk is associated with endothelial dysfunction which is anti-erection. In addition, cassein, the primary protein in milk, is pretty nasty stuff and increases IGF-1, a potential cancer-causer.
NOTE: One contradiction of this are the Masai who historically drank substantial amounts of raw cow's milk and yet experienced a very low rate of heart attacks and stroke. However, they walked and exercised almost constantly, something that is impractical for the typical urban dweller.
There is another reason that I believe that milk is the culprit: the Kuna. The Kuna are one of the world's supercultures that live an existence almost completely free of heart disease and other cardiovascular issues. What is their secret? Experts believe it is cocoa. They drink cocoa (without sugar or milk) throughout their day and have it in teas and drinks almost nonstop. Without the negative effects of milk or sugar, cocoa can do it's arterial magic, lowering blood pressure and increasing blood flow - yes, even to your penis.
Regardless, if chocolate does have a "therapeutic window" where too little and too much are dealbreakers, then chocolate lovers clearly have to monitor themselves. After all, our taste buds are compelling us to have more (and more and more) and we need to put the brakes on in order to get the anti-inflammtory and heart-protective properties.
Or you could just go crazy and enjoy the state of ecstasy...
1) J Nutr, 2008;138:1939-1945, "Regular consumption of dark chocolate is associated with low serum concentrations of C-reactive protein in a healthy italian population"
2) Circulation: Heart Failure, 2010; 3:612-616, "Chocolate Intake and Incidence of Heart Failure: A Population-Based Prospective Study of Middle-Aged and Elderly Women"
4) J of Isfahan Med School, 25(87), "Association between Dairy Consumption and Circulating Levels of Inflammatory Markers among Women"