A study, which combined the results of 42 small clinical trials, found that people fed chocolate or cocoa for a few weeks to months had small dips in their blood pressure and improved blood vessel function.
On average, chocolate eaters shaved a couple points from their blood pressure and showed a small improvement in "flow-mediated dilation" – a measure of how well the blood vessels respond to increased blood flow.
They also had a dip in their levels of insulin, a hormone that regulates blood sugar. High insulin levels are linked to an increased risk of type 2 diabetes. The findings, reported in the American Journal of Clinical Nutrition, are far from the first to connect chocolate to heart health.
A number of widely reported studies have found that chocolate lovers seem to have lower rates of certain heart risks, like high blood pressure. But those types of studies, known as observational studies, cannot prove cause-and-effect. People who indulge in chocolate may have other factors in their lives that explain the better heart health.
In contrast, the new study focused on clinical trials – where researchers randomly assigned people to eat chocolate or not, then watched for changes in chocolate eaters' blood pressure, cholesterol and other heart risk factors.
Chocolate might have benefits
The fact that there were some improvements suggests that chocolate may have some actual benefits, according to the researchers, led by Lee Hooper of Norwich Medical School in the UK.
But Hooper cautioned that the studies in the analysis were small and had their flaws. And possibly most important, none have been large or long enough to show whether there's any effect on a person's risk of heart disease or stroke.
"My take-away message would be that if people like dark chocolate, then eating a little in place of other 'treat' foods is fine, and may be beneficial," Hooper said.
"However," she added, "the evidence is not yet good enough to suggest that we should all be doing this." An expert not involved in the study agreed.
"From a practical perspective it is premature to advise individuals to consume chocolate or cocoa to decrease their risk of cardiovascular disease," said Alice H. Lichtenstein, director of the cardiovascular nutrition lab at Tufts University in Boston.
That's due to a number of reasons, not the least of which is calorie control, according to Lichtenstein.
Chocolate tied to heart benefits
Another is that it's not clear how chocolate would have heart benefits. Compounds called flavonoids are the "presumed" player, Lichtenstein said, but they have not been adequately tested to see whether they are, in fact, effective ways to protect your heart.
And even if they are, Lichtenstein said, "little information is available to the consumer for the level of flavonoids in a specific chocolate product."
Plus, Hooper pointed out, there's a range of plant foods that contain various flavonoids -- including many fruits (like berries, citrus and apples) and vegetables (like kale, spinach and broccoli), nuts, soy, tea and wine. For the current study, Hooper's team pooled data from 42 small clinical trials involving about 1 300 people in all.
That approach is called a meta-analysis, and it allows researchers to draw conclusions based on bigger numbers.
But it also has shortcomings, Hooper's team acknowledges. Each of the trials was different -- including different types of people (healthy in some cases, having chronic health problems like diabetes or heart disease in others), and different ways of testing chocolate's effects.
Are the benefits worth the risk?
Some studies used cocoa drinks, some solid chocolate, and some cocoa supplements. They also varied in how long people were "treated" – but most trials lasted less than six weeks.
Larger, longer-term trials – including ones not funded by the cocoa industry – are needed, Hooper and her colleagues write.
Maybe the biggest question is whether any benefits would be worth the downside of chocolate. Based on these small studies, Hooper's team writes, it could take several hundred calories' worth of chocolate to see effects on insulin and blood vessel function.
And that could mean trouble for your waistline, the researchers point out.
Lichtenstein agreed. "Until we get additional data, it is premature to say that adding hot chocolate fudge sauce to a bowl of ice cream is going to decrease the risk of cardiovascular disease," she said. "What we do know," she added, "is that adding the chocolate sauce without decreasing the amount of ice cream in the bowl is going to lead to weight gain."
For now, Lichtenstein said, if you enjoy a little chocolate in your life, you can probably keep doing so. But don't add it in the hopes of helping your heart.
(Reuters Health, Amy Norton, March 2012)
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