If you eat a whole bar (500 calories),
For the rest of your life.
Oh Heather. I was excited to see this article. It was going to be my best justification for letting a few chunks melt in my mouth ... numerous times a day. It just wasn't meant to be.
Here's the article that Heather posted in comments:
Cocoa, Not Tea, Calms Blood Pressure, Study Says
Here's the study behind the article:
Effect of Cocoa and Tea Intake on Blood Pressure
The above is a meta-analysis, a study of studies, that appeared in the Archives of Internal Medicine on Monday. It pooled 5 studies that investigated the effect of chocolate on blood pressure, and 5 that investigated the effect of tea (mostly black tea). The authors concluded that cocoa can reduce blood pressure, but tea cannot.
But is eating chocolate, daily (since the effects are transient), a practical way to reduce blood pressure?
Here's a run-down of the 5 chocolate studies included in the meta-analysis:
Click for larger.
First, note that the second study of 21 participants didn't change blood pressure. Note also that it used only half the amount of chocolate per day as the other 4 studies. If chocolate is going to have an effect, it looks more likely to do so at intakes of 100g or more per day:
" ... it appears that the amount of the ingested cocoa phenols is essential for the magnitude of the blood pressure reduction, since in the study by Engler et al [second in the above table] administration of about half of the cocoa phenols over the same 2-week period did not affect blood pressure."
How much is 100g of chocolate?
I happen to have my favorite chocolate bar just lying around. How about that. (I have admiration anew for food photographers. In most of the photos I took, the chocolate came out looking like one brown unsegmented blob.)
The whole bar is 100g (550 calories). According to Green&Black's label, there are 2.5 servings per bar:
The piece in the middle is one serving or 40g (220 calories).
The piece to the far right is 2 servings or 80g (440 calories).
(I guess you have to buy another bar to get another full serving. Either that or, heavens, eat more than one serving.)
Back To The Drawing Board
The small number of participants (from 13 to 28) and short durations (about 2 weeks) of these studies, combined with the almost across-the-board lack of blinding (how do you hide the fact that you're feeding someone chocolate?), make this particular set of analyses, for me, unpersuasive. Add that to the number of calories one would have to consume daily (~500), not to mention the cost,1 all for a modest decrease in BP, and it just about eradicates the pro-chocolate take home message for me.
If I was a media outlet, I'd be embarrassed for promoting chocolate based on this analysis. When you consider that Mars, Inc., who recently debuted their high-phenolic chocolate called CocoaVia, partially funded that last study, and a few others, it isn't a stretch to view these media stories as advertisements.
Note: This won't bench the chocolate for me. It may not have a practical effect on blood pressure, but its abundance of polyphenolic compounds are thought to lower cardiovascular disease risk in ways other than via BP. More importantly, it makes me a nicer person to be around.
Update, July 6, 2007: A new study does indeed find that eating a small amount of dark chocolate daily reduces BP. See here.