April 1, 2010 (Nuthetal, Germany) — The largest observational study so far to examine the association between chocolate consumption and risk of cardiovascular disease has found that those who ate the most chocolate--around 7.5 g per day--had a 39% lower risk of MI and stroke than individuals who ate almost no chocolate (1.7 g per day) [1].
Lead author Dr Brian Buijsse (German Institute of Human Nutrition, Nuthetal, Germany) told heartwire : "This shows that habitual consumption of chocolate is related to a lower risk of heart disease and stroke that is partly explained by blood-pressure reduction. The risk reduction is stronger for stroke than for MI, which is logical because it appears that chocolate and cocoa have a pronounced effect on BP, and BP is a higher risk factor for stroke than for MI." Buijsse and colleagues report their findings online March 31, 2010 in the European Heart Journal.
However, Buijsse cautions that only small amounts of chocolate were associated with the benefits and it is too early to give recommendations on chocolate consumption: "Maybe it's a boring message, but it's a little too early to come up with recommendations, because chocolate contains so many calories and sugar, and obesity is already an epidemic. We have to be careful." However, he added, that if people did want to treat themselves, they would be better off choosing small amounts of chocolate, preferably dark chocolate, over other sweet snacks. "We know it is the cocoa content in chocolate that is important, so the higher the cocoa content, the better."
Dr Steffen Desch (University of Leipzig, Heart Center, Germany), who was not involved with this study but who has performed research on the effects of chocolate on blood pressure, told heartwire : "This is an interesting study that adds to the growing body of evidence that flavanol-rich chocolate might be associated with health benefits. Several epidemiological studies (including the Zuphten Elderly Study, by the same first author) and even more physiological trials have been published before."
"What is missing now is a large-scale randomized trial of flavanol-rich chocolate versus control. The most reasonable end point would probably be the change in blood pressure between groups." However, Desch added, "the major problems in designing such a study are the lack of funding and finding an appropriate control substance. To the best of my knowledge, there is no commercially available flavanol-free chocolate that offers the distinct bitter taste and dark color inherent to cocoa-rich chocolate."
Biggest Chocolate Consumers Had Lowest Blood Pressure
Buijsse and colleagues followed 19 357 people, aged between 35 and 65, who were participants in the Potsdam arm of the European Prospective Investigation into Cancer (EPIC). They received medical checks, including blood pressure and height and weight measurements at the start of the study (1994–1998), and they also answered questions about their diet, lifestyle, and health, including how frequently they ate 50-g bars of chocolate.
The research was conducted before the health benefits of chocolate and cocoa were recognized, so no differentiation was made between milk, dark, and white chocolate in the study. But in a subset analysis of 1568 participants later asked to recall their chocolate intake over a 24-hour period, 57% ate milk chocolate, 24% dark chocolate, and 2% white chocolate.
Participants were divided into quartiles according to their level of chocolate consumption. Those in the top quartile, eating around 7.5 g of chocolate a day, had blood pressure that was about 1 mm Hg (systolic) and 0.9 mm Hg (diastolic) lower than those in the bottom quartile.
In follow-up questionnaires, sent out every two or three years until December 2006, the participants were asked whether they had had a heart attack or stroke, information that was subsequently verified by medical records from general physicians or hospitals. Death certificates from those who had died were also used to identify MIs and strokes.
"Our hypothesis was that because chocolate appears to have a pronounced effect on blood pressure, chocolate consumption would lower the risk of strokes and heart attacks, with a stronger effect being seen for stroke,” explained Buijsse.
Those Eating Most Chocolate Had Half the Risk of Stroke
During the eight years, there were 166 MIs (24 fatal) and 136 strokes (12 fatal); people in the top quartile had a 27% reduced risk of MI and nearly half the risk (48%) of stroke, compared with those in the lowest quartile. The relative risk of the combined outcome of MI and stroke for top vs bottom quartile was 0.61 (p=0.014).
The researchers found that lower baseline blood pressure explained 12% of the reduced risk of the combined outcome, but even after taking this into account, those in the top quartile still had their risk reduced by a third (32%) compared with those in the bottom quartile over the duration of the study.
To put this in terms of absolute risk, Buijsse said if people in the group eating the least amount of chocolate increased their chocolate intake by 6 g a day, 85 fewer heart attacks and strokes per 10 000 people could be expected to occur over a period of about 10 years.
He says it appears that flavanols in chocolate are responsible for the beneficial effects, causing the release of nitric oxide, which contributes to lower BP and improves platelet function.
Dr Frank Ruschitzka (University Hospital, Zurich, Switzerland) agrees. He said in a European Society of Cardiology statement [2]: "Basic science has demonstrated quite convincingly that dark chocolate particularly, with a cocoa content of at least 70%, reduces oxidative stress and improves vascular and platelet function."
Only Small Amounts of Chocolate Beneficial; Don't Eat Too Much
Buissje said this work builds on his earlier small trial--the Zuphten Elderly Study--performed in 500 men in Holland, which showed that chocolate consumption lowered overall cardiovascular mortality. "Due to the small size of this study, we were not able to differentiate between stroke and MI in this, but now we are able to look at stroke and MI separately, so it's a nice addition," he notes.
And the findings are in line with an intervention study that showed that eating around 6 g of chocolate a day--one small square of a 100-g bar--might lower CV disease risk, he says. "So the effects are achieved with very small amounts."
British Heart Foundation dietician Victoria Taylor made the same point: "It's important to read the small print with this study. The amount consumed on average by even the highest consumers was about one square of chocolate a day or half a small chocolate Easter egg in a week, so the benefits were associated with a fairly small amount of chocolate.
"Some people will be tempted to eat more than one square; however, chocolate has high amounts of calories and saturated fat . . . two of the key risk factors for heart disease," she noted in a statement [3].
Ruschitzka similarly urged caution: "Before you rush to add dark chocolate to your diet, be aware that 100 g of dark chocolate contains roughly 500 calories. As such, you may want to subtract an equivalent amount of calories, by cutting back on other foods, to avoid weight gain."
