But chocolate lovers shouldn't take the news as license to indulge. Chocolate only helped people who already had risk factors for heart disease, and only when consumed in modest amounts, Dr. Rutai Hui of the Chinese Academy of Medical Sciences and Peking Union Medical College in Beijing and colleagues found.
Several studies have suggested that chocolate may be good for you. One study released in March showed that among 19,300 people, those who ate the most chocolate had lower blood pressure and were less likely to suffer a stroke or heart attack over the next 10 years. But like the new analysis, that research came with caveats; the difference in chocolate consumption between the top and bottom chocolate-consuming groups was around 6 grams, or about one-seventh of a Hershey's milk chocolate bar.
In the new analysis, Hui and colleagues searched the medical literature to find studies that looked at how cocoa affected blood fats, or lipids, and found eight trials including 215 people. When all studies were analyzed together, the researchers found eating cocoa cut levels of LDL, or "bad" cholesterol, by about 6 mg/dL and reduced total cholesterol by the same amount. But cocoa had no effect on cholesterol in the three highest-quality studies.
Further analysis showed that only people who ate small amounts of cocoa, an amount containing 260 milligrams of polyphenols or less, experienced cholesterol lowering effects; people who consumed more showed no effect.
Polyphenols are antioxidant compounds found in fruits, vegetables, chocolate and red wine. A 1.25-ounce bar of milk chocolate contains about 300 milligrams of polyphenols.
The researchers also found that healthy people didn't get any cholesterol-lowering benefits from cocoa, but people with risk factors for heart disease, such as diabetes, saw their LDL cholesterol and total cholesterol drop by around 8 mg/dL each.
Eating moderate amounts of cocoa could be "a worthwhile dietary approach" for preventing high cholesterol in certain groups of people, Hui and colleagues conclude in a report in the American Journal of Clinical Nutrition.
"Future research efforts," they say, "should concentrate on higher-quality and more rigorous randomized trials with longer follow-ups to resolve the uncertainty regarding the clinical effectiveness. Then we can really eat chocolate without feeling guilty."