Monday, June 11, 2012

Can Chocolate Save You From Heart Attack?

The media says yes. Science says maybe. In the end, you decide. Here are the facts:

A truffle treatment for heart disease is imminent. That's what a recent article suggests, headlined in the New York Daily News as: "Dark chocolate cuts heart deaths; Study shows benefits for high risk cardiac patients." 

The funny thing is, the cited  study does not show what the media geniuses claim it does. So, let's look at this master piece of research journalism and ...
do a little fact check. [tweet this].

The cited study was performed by Ella Zomer and colleagues in Australia [1]. The researchers wanted to answer the question, what the daily consumption of dark chocolate would do to the heart health of a given population. Contrary to what you might believe, the researchers didn't pit chocolate eaters against abstainers. They simply ran an algorithmic model on the computer. In this case, a 10-year forward projection of what might happen, heart-wise, in a given population. Nothing wrong with that, as long as we keep in mind that such models are based purely on assumptions. You need to know those assumptions before you start investing a part of your daily food budget into chocolate.  So, let's take a more detailed look than the anonymous AFP writer did, whose master piece the NYDN bought to educate their readers.

The researchers selected the data sets of 2013 AusDiab study participants who were free from cardiovascular disease and diabetes, but who had the metabolic syndrome. The latter is not a disease in itself but an arbitrary risk definition along 5 risk factors: abdominal obesity, elevated triglycerides, blood sugar and blood pressure, and low "good" cholesterol (high-density lipoprotein, HDL). Have any three of those 5, and you are said to have the metabolic syndrome. 

To calculate the risk of suffering a heart attack or stroke, the researchers used the algorithms developed from the Framingham study. Those risk calculations are widely used in clinical practice. They inform your doctor about the need and urgency of treating you to prevent a heart attack or stroke. I have written about the sense and nonsense of such risk factors in my earlier post "When risk factors for heart attack really suck!".  Now, in order to calculate what the blissful consumption of chocolate will do to prevent such heart attacks, we need some more data. The researchers took those from 13 studies, which investigated the effects of chocolate consumption on blood pressure and on cholesterol levels.  

Now here is the first problem: While the Framingham study's algorithms have been tuned on the correlation of risk factors with with hard outcomes (real heart attacks and strokes) for more than half a century, the longest clinical trial on the effects of chocolate lasted just 18 weeks. Meaning, for the effects of chocolate consumption, we don't have anything remotely equivalent to the Framingham data. And we will probably never have, because it is difficult to imagine a study in which we expose half the participants to a daily chocolate load for many years, while the other half doesn't get any, with us waiting and watching what happens in terms of heart disease. Which is to say, the 13 studies used by the researchers are the next best choice. It informs us about the effects of chocolate consumption on blood pressure and cholesterol. The researchers plugged those data into the mathematical model, together with the Framingham algorithms and the life tables available for their Australian population. The entire model is based on a so-called "Markov model", which is simply a probability-based simulation of processes over time. 
Now that we are clear about the methods and assumptions, let's look at what you read in the article: 
"Australian researchers have found that eating a block of chocolate daily over 10 years has 'significant' benefits for high risk cardiac patients and could prevent heart attacks and strokes." Well, didn't I just tell you that the participants' data sets had been selected such that only those who were not cardiac patients, were considered in the model? Yep, that's what it says in the methods section of the study. But methods are tedious to read and, admittedly, a bit difficult to understand sometimes, so we forgive our writer for this little slip-up. Also, none of the participants had eaten a chocolate bar daily for 10 years, so really nobody could "have found" what that would have done for heart risk. But let's not dwell on such trifles. On to the next paragraph:

"A study .... found that the consumption of ... chocolate ... was an effective measure to reduce risk." Whoa, that one we can't forgive. What we do have are 13 studies, which show that a daily chocolate consumption of about 100 grams (3.5 ounces) reduces systolic blood pressure in hypertensive people by 5 mmHg on average, and total cholesterol by 0.21 mmol/L (8mg/dL). What these studies do not show, is a reduction of risk for heart disease, that is, a reduction of real heart attacks and strokes. 

Given the size of the improvements, I have serious doubts about those effects anyway. What I observe as blood pressure measurements in the daily clinical practice, a 5mmHg difference is within the error margin of many physicians' and nurses' measurement skills. And a 0.21 mmol/L difference in cholesterol is deep within the bandwidth of variations, which most people would see if they were to measure their cholesterol levels for a few days in a row. We have done that in our lab, and found the intra-individual variability to be way above those 0.21 mmol/L. In other words, if your cholesterol level is measured today, and tomorrow, and day after tomorrow, the values will vary by more than those 0.21 mmol/L, even if your blood was drawn at the same time of day, and always after an overnight fast.  

On to the next paragraph: "Lead researcher Ella Zomer said the team found 70 fatal and 15 non-fatal cardiovascular events per 10,000 people could be prevented over 10 years if patients at risk of having a heart attack or stroke ate dark chocolate." Throwing out numbers always looks good, but what do these numbers mean for YOU? I operate under the assumption that you are not interested in the 85 events among the 10,000 people, but that your interest is with the ONE possible event in YOU, right? 

OK, let's look at that. Of course, I don't have the data set of Zomer and colleagues, but we can make quite an educated calculation using the Framingham risk algorithm, the average risk profile of the participant and the researchers' statement of the effect size: 85 prevented events per 10,000 people. And here is what it means to you: 
If your profile is that of the average participant (that is, you are 53 years old, have a systolic blood pressure of 141 mmHg, total cholesterol of 6.1 mmol/L and HDL-cholesterol of 1.2 mmol/L), your chance of suffering a heart attack or stroke over the next 10 years would be roughly 10%. 
Eating chocolate every day would reduce this risk by a whopping 0.3% to 9.7%. Wow. 

So, over to you: do you agree with the article's next paragraph, where it quotes the researchers as saying that "Our findings indicate dark chocolate therapy could provide an alternative to or be used to complement drug therapeutics in people at high risk of cardiovascular disease."? I can already hear people telling their friends about the chocolate therapy they are on. Sounds fully compliant with the researchers' next statement "... here is a dietary alternative which may be quite appealing to a lot of people. In fact, chocolate studies have shown really good compliance rates." 

Well, except for the morsel about compliance rate, I don't buy it. Think about it. 100 grams of chocolate pump 550 kcal into your body (coincidentally the same as a Big Mac), delivered by  50 grams of sugar and 36 grams of fat, most of it saturated. And one more thing: the ingredient which, we believe, is the cause of chocolate's beneficial effect is the flavanol content. I won't go into details about this member of the flavonoid family, but suffice it to say, you'll find it in effective doses only in chocolates with at least a 70% cocoa. That is bitter chocolate. Also known as dark chocolate. But the latter name is already a potential for deception by the manufacturer. The flavanols are inherently bitter, which is where bitter chocolate originally got its name. To make it more pleasant to your taste buds, manufacturers can take the flavanols out and compensate by making the chocolate darker by other means. The end effect is a dark chocolate, which delivers all the sugar and fat and calories but none of the benefits for which you might have chosen it. 

Also, the flavanol content of cocoa can vary substantially, depending on where it comes from. No wonder, you find nothing written about your favorite chocolate's flavanol content on its nutrition label. And by the way, you encounter the flavonoid superfamily, of which chocolate's flavanols are a member, in virtually all fruits and vegetables. Often in concentrations which far exceed what chocolate has to offer. 

So here is what we see in this article of the New York Daily News: there is public health, there is you and then there is the media. To public health, 85 avoided heart attacks and strokes per 10,000 people is worth something, particularly when public health doesn't need to pay for it. Because you do, by buying your "chocolate therapy". Public health couldn't care less whether your 0.3% risk reduction is meaningful for YOU. But you care, I presume. Which is why I find it regrettable that you have to deal with the degree of misinformation doled out by those media geniuses, who, like public health, are not interested in YOU. They are interested in your subscription and your dollar. 

So, if you think that some of your friends would benefit from knowing about this, then send them this post. If you or they have an elevated risk for heart disease, there are many proven ways to reduce that risk. Eating chocolate is not one of them. [tweet this].  

1. Zomer, E., et al., The effectiveness and cost effectiveness of dark chocolate consumption as prevention therapy in people at high risk of cardiovascular disease: best case scenario analysis using a Markov model. BMJ, 2012. 344(may30 3): p. e3657-e3657.

Zomer, E., Owen, A., Magliano, D., Liew, D., & Reid, C. (2012). The effectiveness and cost effectiveness of dark chocolate consumption as prevention therapy in people at high risk of cardiovascular disease: best case scenario analysis using a Markov model BMJ, 344 (may30 3) DOI: 10.1136/bmj.e3657
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  1. There actually is a chocolate that certifies the amount of flavanols on their label. They also use no processed sugars, bad fats, preservatives, waxes nor fillers. You can get 1000 flavanols for as little as 100 low glycemic calories. And i tastes so good you think you are doing something wrong! If fact, the US Trademark Office have given this company the trademark on the words, "healthy chocolate". You can find all 8 products on my site -

  2. Diana, thanks for your input. Could you kindly let me have a copy of the nutrition label which specifies the cocoa content? I can't find that info on your website. Thanks a lot and cheers.

  3. nice posting.. thanks for sharing.


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