Even small amounts of dark chocolate might help to prevent the sort of blood clots that cause heart attacks and strokes, a finding that researchers say could make the treat a routine part of a heart-healthy diet.
The benefits of a class of chemicals called flavonols, derived from cacao beans, have been emerging from research for decades. But previous studies have been laboratory investigations involving large doses of flavonols -- equivalent to eating several pounds of chocolate a day.
Diane Becker, lead author of a study presented yesterday, said it is the first one to find a significant effect in people who ate chocolate in amounts that chocolate lovers more typically consume.
"Some dark chocolate looks like it's healthy in small quantities," said Becker, who presented her findings at a scientific meeting of the American Heart Association in Chicago. "Halloween basket chocolate and vending machine chocolate are definitely not on this agenda."
Becker is a professor of health policy and management at the Johns Hopkins School of Medicine and the Bloomberg School of Public Health. She is also a vegetarian and a self-described "chocoholic."
"I'm not guilty about it," she said, "but I was before -- before I understood and knew a lot about it. ... In its pure form, it's really good for you."
Each day around 4 or 5 p.m., Becker, 63, takes the equivalent of half a Hershey bar -- but it's a dark, low-fat, low-sugar variety of chocolate. She dunks half of it in a skim, decaf latte, then chases the coffee with the other half.
"The reason I do it is because I'm so proscriptive about everything else in my diet. ... I look forward to that all day," she said.
Her understanding of chocolate cravings led to the findings presented yesterday. They grew out of a much broader study of how genes influence the way aspirin delays clotting time by slowing the activity of blood platelets.
Platelets are a key component of the blood's clotting mechanism. Their abundance and "stickiness" determine how easily they form the clots needed to stop blood loss after injury.
But in patients with blood vessels narrowed by cardiovascular disease, easy clotting can cause serious, even fatal complications, including heart attacks and strokes.
Becker's study, called GeneSTAR (for Genetic Study of Aspirin Responsiveness) was designed to find genetically based patterns in blood clotting mechanisms and to identify which of 1,200 participants responded best to aspirin therapy. All had a "slightly" elevated risk of heart disease.
To help isolate the effect of the aspirin, Becker's team instructed participants to avoid flavonol-rich foods for up to two weeks before the tests -- foods such as chocolate, coffee, red wine, strawberries and pineapples.
But Becker knew some would cheat. In fact, many confessed they would probably be unable to give up their daily chocolate fix.
So, Becker and her team decided to use their subjects' craving to examine the impact of normal chocolate consumption on platelet activity.
They were not disappointed: 139 of the 1,200 participants cheated. They repeatedly confessed to the investigators and also kept food diaries. From both, Becker's team estimated the contraband's cocoa content and processed the data to isolate and quantify the effect of the chocolate on the participants' platelet activity.
Their measure of the clotting time for the "chocolate offenders," as Becker called them, showed it was significantly slower than for those who abstained. The difference averaged just seven seconds, but it was evidence that normal chocolate consumption has a positive impact.
More importantly, even after controlling for everything else these people ate, a urine test for the waste products of platelet metabolism showed a real platelet suppression effect from flavonol ingestion.
There was a "major difference between those who ate chocolate and those who didn't," she said.
The more they ate, the greater the slowdown in platelet activity. That should translate into a significant lowering of the risk of dying from a heart attack.
A large study in the Netherlands, reported earlier this year, found a 50 percent reduction in heart disease mortality among older Dutch men who ate the most dark Dutch chocolate.
That benefit doesn't come solely from the flavonols' effect on platelets, Becker said. Researchers know that flavonols also lower blood glucose and "bad" cholesterol and enhance the function of the epithelial cells that line blood vessels. That helps the vessels expand and contract to control blood pressure and nourish tissues, including the heart.
"Increasing the time it takes for clots to form in diseased vessels is highly effective in reducing myocardial infarction [heart attacks] and cardiac death," Becker said.
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