Chocolate and Blood Pressure -- Some Bitter Results

Henry R. Black, MD


November 22, 2010

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Hi. I'm Dr. Henry Black. I'm Clinical Professor of Internal Medicine at New York University School of Medicine, a member of the Center for the Prevention of Cardiovascular Disease, and immediate past President of the American Society of Hypertension.

Today I want to speak about a subject that I think is close to all our hearts: chocolate. There have been some interesting epidemiologic studies over the past few years that suggest that people who ingest a reasonably large amount of chocolate do better and have lower blood pressures than people who don't, and that eating some chocolate products can actually reduce blood pressure by a reasonable amount, maybe as much as 4.5 systolic and 2.5 diastolic, which would be impressive for something that we actually like to do.

The problem is that all of the studies -- epidemiologic, observational, and clinical trials -- haven't been well controlled. So a group in Holland decided to test this in a very extensive and extremely well-done way.[1] They did a so-called "crossover" study. What that means is that they tested a couple of different therapies. In this case there were 3, and each patient took one of them. Then that therapy washed out and the patient took another, and then the patient took the third. The current design had 3-week ingestions of placebo, a cocoa drink, or a usual dose of cocoa drink plus theobromine, which is the compound in chocolate thought to prevent some of the cardiovascular complications. What theobromine seems to do is release nitric oxide and reduce some of the enzymes that cause some cardiovascular constriction and actually cause vasodilation. So theobromine may be the reason that cocoa-containing products might actually have a beneficial effect on blood pressure.

The crossover design was quite well done. The participants began with placebo, a high dose or low dose of the theobromine, plus a cocoa drink or sham cocoa drink. At the end of the 3-week period, the participants switched to another therapy and then the third therapy. In all crossover studies, the time in between -- in this case it was a 2-week washout -- has to be taken into account because there could be an effect related to which therapy was given first, second, or third.

They also did some very elegant hemodynamic monitoring, including ambulatory blood pressure monitoring (ABPM). They looked at central hemodynamics, augmentation index, pulse-wave velocity, and other very elegant ways to assess the effects of the compounds being tested -- be it drugs or, in this case, a nutraceutical or a product that could turn into a drug as we proceeded.

They didn't need a large study. Sometimes when something is as well done as this, a small study is good enough -- it's not an outcome study. They initially recruited 42 people, and 41 of them completed the trial. They randomized them to start with the placebo, a low dose or a usual dose, and start with a high dose of theobromine added to the cocoa drink. Then they switched them in a random order.

They had very surprising results. For one thing, the group that got theobromine, or cocoa plus theobromine, in either dose had an increase in heart rate and an increase in blood pressure when measured peripherally and when measured on ABPM. That's not a good thing. An increase would be exactly what we want to avoid, and any drug that comes along that's supposed to be helpful for cardiovascular prevention had better not raise blood pressure; look at torcetrapib.

What was different and what was very interesting was that central hemodynamics, the measures of augmentation index and central blood pressure, went in the opposite direction. Now, there are some people who think that central blood pressure and hemodynamics measured centrally are more important than what we measure peripherally. We all know that office blood pressures can be a little unreliable, but they did ambulatory blood pressure monitoring, 24-hour monitoring, which is a much better way to understand a full 24 hours' effect on blood pressure.

These individuals were relatively low risk: They had high-normal blood pressure (prehypertensive) or had stage I hypertension. They were relatively young. They were thin. They were not allowed to drink more than 4 cups of coffee a day. They were allowed to eat only milk chocolate, not white chocolate, which had been one of the control groups in earlier studies. They were not allowed to have any alcoholic beverages or tea or coffee the day before these measurements were made. A lot of people were willing to do this.

The problem now is, what do we do with this? Is there something different about chocolate bars, or chocolate, or milk chocolate, or white chocolate, or who knows? Or should we not be focusing so much on cocoa?

In any case, sometimes when we put our concepts to the test in a reliable study, we don't get what we expect. Like everyone else, I would like to think that chocolate is a good thing and that we could eat it whenever we wanted and that it would help us. I'm afraid we can't say that yet.

Thank you.


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