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Study: Dark chocolate improves blood vessel health


4 Star

Study: Dark chocolate improves blood vessel health

Our Review Summary

This news report describes a study which suggests that dark chocolate might be healthy for the heart. It provides some background on flavonols, the constituent in dark chocolate that might be beneficial, notes some of the potential harms associated with this "chocolate therapy," and includes interviews with three experts who are mostly enthusiastic about the study’s findings. Yet the story fails to examine the rigor of the new evidence.


The researchers enrolled 39 people. Were there enough subjects to muster the statistical power needed to answer their question? Could the improvements in blood flow be the result of chance? Did the researchers account for other factors that might affect arterial blood flow? What are the true benefits of improvements in blood flow to an arm? Is there research to suggest that they correspond to any outcome of clinical significance, such as rates of heart attack, stroke, or death? What else could patients do to derive the same apparent benefit without the fat and calories of chocolate? Could they take a low-cost, fat-free, calorie-burning walk once a day? The story answers none of these.


The study appears to be one small, preliminary step in the investigation of a scientific hypothesis. Readers should not be left with the impression that consuming chocolate every six hours is a sound, scientifically proven, good idea.



Does the story adequately discuss the costs of the intervention?

Not Applicable

Thought there was no discussion of cost, most people have a general idea how much cocoa costs.

Does the story adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

The story fails to describe the improvement in blood flow in absolute terms, instead noting only relative or percent improvement (e.g. 37% compared to baseline for consumption of artificially sweetened cocoa). The reported 37% improvement is much greater than that reported in a press release from the American College of Cardiology (2.4% over baseline); the reason for the discrepancy is unclear.

Does the story adequately explain/quantify the harms of the intervention?


The story notes that chocolate is laden with fat and calories, potentially harmful in people who are already overweight or obese.

Does the story seem to grasp the quality of the evidence?

Not Satisfactory

This story is based on the preliminary results of a small, unpublished study presented at a national cardiology meeting. The researchers fed three different foods (two types of chocolate and a placebo whey powder) to 39 people during three separate 6-week trials, and then after each trial used ultrasound to measure arterial blood flow in the arms of their subjects, a test that purportedly “corresponds well to heart disease.” Unfortunately, the story says little about the methodological shortcomings inherent in such a research design. Are there enough subjects in the study to muster the statistical power to answer the question being asked—or could the improvements in blood flow be the result of chance? Did the researchers account for other factors that might affect arterial blood flow, such as exercise routines? Is there research to suggest that the observed differences in arterial blood flow correspond to any outcome of clinical significance, such as rates of heart attack, stroke, or death? This news report says nothing about such potential limitations. We suspect many observers would say that this study simply raises an interesting question, but certainly doesn’t answer it. Despite the researcher’s assertion–"This tells you that it (cocoa) is cardio-protective"–the data seem only to show that cocoa simply relaxes smooth muscle in the arm.

Does the story commit disease-mongering?


The story contains no obvious elements of disease-mongering.

Does the story use independent sources and identify conflicts of interest?


The report cites three sources and their credentials, but mentions a potential conflict of interest for only the lead author, who received funding from Hershey and the CDC. It is impossible to judge the independence of the other sources. Nonethless, we'll give the story the benefit of the doubt.

Does the story compare the new approach with existing alternatives?

Not Satisfactory

The report neglects to mention “treatments” other than chocolate that might improve the endothelial function of these subjects. Among these is low-cost, fat-free, calorie-burning exercise.

Does the story establish the availability of the treatment/test/product/procedure?


Though it would seem reasonable to think that the Hershey’s cocoa mixes used in this study are available on grocery store shelves, it’s impossible to know. (It’s not readily clear from Hershey’s web site either.) Nonethless, we'll give the story the benefit of the doubt on this criterion.

Does the story establish the true novelty of the approach?


The story says this is the “latest in a growing number” of studies in this area.

Does the story appear to rely solely or largely on a news release?


The report includes some information that was widely available in press releases, but also additional information that goes beyond the press releases.

Total Score: 6 of 9 Satisfactory


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