Friday, July 06, 2007

A Small Daily Dose of Dark Chocolate Lowers Blood Pressure

Finally, a study about chocolate with results I can apply. See those two small chunks of dark chocolate in FRE's hand? That amount was just found to be effective at reducing blood pressure if eaten daily.1

I'm very excited.

This is the first study to report this benefit using such a small intake of chocolate. Previous studies had us eating about a quarter pound (100 grams) of chocolate daily. Daily is an operative word here. Slack off eating that 500-calorie-bar daily and no effect on blood pressure would be seen. I don't know anyone who could fit 500 extra calories into their diet - Every Single Day - and not gain weight or displace other needed nutrients. That's why this study is so exciting to me. I've seen lots of chocolate studies but never one I allowed to significantly change my eating behavior, or one that I felt responsible in recommending to others.

Study Basics
  • Randomized, controlled, investigator-blinded (you can't blind the chocolate eaters).
  • Participants were 44 white, older (56 to 73 years of age), mildly hypertensive adults recruited from a primary care clinic in Germany.
  • Intervention was daily consumption of 6.3 grams (30 calories) of dark chocolate; control group received white chocolate (which had no BP-lowering effect).
  • After 18 weeks, dark chocolate eaters reduced their systolic BP by an average of 2.9 mm Hg, their diastolic by 1.9 mm Hg. (This is no pittance.2)
Why This Study Excites Me
  • After 18 weeks, everyone (100%) who consumed dark chocolate experienced a reduction in blood pressure.
  • Retention was 100%. No participants dropped out. That's something for an 18-week intervention. Perhaps the pill was easy to swallow.
  • Participants kept daily food diaries. This helps rule out effect from other dietary components, or a change in eating habits during the study. This level of food intake assessment is unusual and expensive, but it adds credence to the results.
  • The daily chocolate dose did not result in weight gain.
  • The study documented the likely mechanism: Some ingredients in dark chocolate, possibly cocoa polyphenols, increase circulating levels of a compound called S-nitrosoglutathione. This chemical is a vasodilator, it can widen blood vessels allowing increased blood flow.

How to Apply Their Results
  • Eat dark chocolate. Not white chocolate, not milk chocolate, not chocolate with a low cocoa content. Aim for a 70% cocoa content or higher.
  • Eat no more than about 6.3 grams (the amount shown in the photo), unless you can afford the calories.
  • Eat the chocolate daily. This is important; think of it as a pill. The BP-lowering effects in this study were progressive: No effect was seen for the first 6 weeks, the strongest effect was measured at the end of the study (18 weeks). So you'll need a daily dose to reach and maintain the BP-lowering effect.
1 Effects of Low Habitual Cocoa Intake on Blood Pressure and Bioactive Nitric Oxide
The authors of this study are the same, mostly, as those who conducted the one on chocolate and blood pressure that I discussed here back in April.
2According to these researchers, this reduction would reduce stroke mortality in the population by 8% and cardiovascular disease mortality by 5%.
It's also equivalent to the BP reduction (3 to 4 mm Hg systolic, 1 to 2 mm Hg diastolic) seen in the HOPE (Heart Outcomes Prevention Evaluation) Study which was achieved using an ACE inhibitor, and which reduction, although modest, was thought to contribute to the reduction in heart attacks seen in this group of over 9500.
Lastly, as Mike prompted in comments, there may be a dose-response mechanism working, meaning the more cocoa you eat, the greater your BP reduction. Previous studies that used more than the 6.3 grams in this study found greater reductions. This is not a consumption license.

Photo: Homegrown. The chocolate is Green&Black's, 70% cocoa.


Unknown said...
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Unknown said...
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Unknown said...
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Unknown said...

Heyy! this is great, thanks! +D ....
But, one question .... :D
Why do u suggest a 70% cocoa product? :) :) ... y not perhaps a 60 maybe!? :D ... I mean, i know it's lowering the cocoa content... +D and the higher, the better! :D .... But my question is, why do you say *70* as being the ideal *start percent* is all i would like to know.... (: ..

Thanks once again! :D ....

Bix said...

Sure, go for 60%. I think you could go down to 50% cacao and still derive benefits. The 70% was a conservative figure; it allows you to consume fewer calories for similar effect. Also, chocolate varies in polyphenol content, even among chocolate with the came cacao content, so 70% is a good insurance.

Or you could eat 3.1 grams of pure cacao bean/day. But it would be bitter!