In laboratory studies, researchers have linked various possible benefits to cocoa. For most purported effects, however, "we're still missing the definitive studies," said Carl L. Keen, a professor of nutrition and internal medicine at the University of California, Davis, who has collaborated with chocolate giant Mars. Placebo-controlled trials involving human volunteers have begun to answer a few key questions.

Can cocoa flavanols improve blood flow? "Without a doubt, if you feed people flavanol-rich cocoa, you will be able to measure improvements in blood flow," said Mars's chief scientist, Harold H. Schmitz.

His claim is supported by several small trials, including the only one that Schmitz said he knows of that was not funded by the chocolate industry. In that study, published in the Journal of the American College of Nutrition last year by researchers from the University of California, San Francisco, and Tufts University, 21 healthy volunteers ate 1.6 ounces per day of either Dove Dark Chocolate (provided by Mars) or another dark chocolate that was low in flavanols. After two weeks, those eating the Mars product had arteries that were slightly more dilated a condition associated with healthy blood vessels.

Can they lower blood pressure or cholesterol? In that trial, no benefit was evident in blood pressure, cholesterol or antioxidant activity. However, a few industry-sponsored trials, including some of Keen's work, suggest that flavanol-containing dark chocolates and cocoa beverages can lower blood pressure, at least in people with hypertension. A couple of trials found unconfirmed improvements in cholesterol levels, and several suggest reduced oxidation of cholesterol, a benefit of antioxidant activity.

In a separate, unpublished study that Keen and Mars researchers presented in November to the American Heart Association, 35 volunteers who ate two CocoaVia bars daily for six weeks enjoyed, on average, a 6 percent drop in LDL, the so-called bad cholesterol. Another 35 participants ate a different bar and showed no change in cholesterol. Neither group experienced a change in blood pressure or in weight. All volunteers initially had high cholesterol.

Can chocolate, like aspirin, prevent blood clots? Industry research suggests that consuming cocoa flavanols makes platelets less prone to clumping together. And at least one study reported that drinking cocoa daily reduced inflammation in blood vessels, although slightly less than low-dose aspirin did. In theory, those effects could cut the risk of clots that cause strokes, heart attacks and other problems. However, no study has lasted long enough or been large enough to show such an effect.

Is cocoa anti-diabetic? An Italian study published last month in the journal Hypertension was the first to report that volunteers who ate dark chocolate became more responsive to insulin. Because high sensitivity to insulin guards against type 2 diabetes and other cardiovascular problems, said Penny Kris-Etherton, a cardiovascular nutritionist who has received industry funding, that discovery could be important -- if it can be confirmed by other researchers.

Can cocoa fight cancer, cough and chronic fatigue? These are some of the provocative possibilities raised by lab findings. The cancer research is of particular interest, said Schmitz, but "we're not jumping up and down talking about it, because it's just the beginning."

-- Ben Harder