I am going to tell you about a recent study* that tested to see if chocolate, dark or milk, improved walking for persons diagnosed with PAD. I am omitting a lot of important scientific information, but you can read the journal article here.
PAD stands for peripheral artery disease, which I have blogged about previously; a person with PAD has limited blood flow in the arteries of the lower legs because the arteries are constricted or narrow. If you or someone you know has PAD (20% of people over the age of 70 who live in Western countries do; see citation 2 in the research publication), you are likely familiar with the term Intermittent Claudication. During exercise or walking, a person with PAD may experience severe pain in their lower legs because of a lack of blood flow, this is Intermittent Claudication.
Intermittent Claudication limits the activity of persons with PAD and finding a way to reduce this, which means addressing the blood flow problem, is very important. Loffredo et al (physician/scientists in Italy) knew, from other studies, some of the physical, under the skin things that happen in persons with PAD (e.g., substances that act on the inner lining of the blood vessels are impaired, toxic residue from cellular actions build up because the body doesn't clean them out (oxidative stress)). The scientists were particularly interested in the oxidative stress. Previous research had found that oxidative stress was a main reason for the constricting of the lower leg arteries, the accompanying pain and the inability to walk long or far. [there is much more to the mechanisms and I refer you to the article for a more thorough explanation]
The terms more of us may be familiar with are "free radical damage" and "antioxidants." Antioxidants cause chemical reactions in the body, under the skin, that, in a series of interactions, can reduce the oxidative stress (caused by free radicals). One powerful antioxidant (polyphenal type) is cocoa. In past studies, cocoa has helped to dilate (make bigger) arteries, thus leading to improved blood flow. If the blood flow improves, the pain should reduce and people with PAD might walk farther, longer, or both. That is what the scientists wanted to test. If they gave people chocolate, would their condition improve, at least for the short (immediate) term.
The Loffredo et al study was very small and considered only a proof of concept - in other words, no causation can be implied about the chocolate! The scientists invited persons with moderate to severe PAD, who were stable, and who were not smokers, to participate. After the initial screening, which did 'reject' 5 persons because they smoked (which is untenable to me - that they smoke when they have blood flow problems). Only 20 people participated in the study and each person participated in both parts (i.e., crossover design) and there was no control group (another reason why it is just a proof of concept study). I have to make an aside before I talk about the results.
Researchers always give a little information about the sample in a study. This allows us to see how much those people are like us, or like some larger group. In looking at these sample characteristics, the average age was 69 and there were twice as many men as women, 90% had high cholesterol and all of them were on statin medications (among other drugs), the average BMI was 27 (overweight) and most tellingly, 80% of the people in this study were former smokers.
The scientists used several tests that diagnose and monitor PAD, including an Ankle Brachial Index and an FMD (flow-mediated arterial dilation), as well as a treadmill test, to assess the main effect (a reduction in Intermittent Claudication, increase in walking time or distance). They collected blood and did additional tests to determine the mechanism of effect - for example, how did the chemicals in the blood (neurotransmitters and such) change after the intake of either type of chocolate and does that change explain the main effect, which is walking distance and time. The participants were tested once after they ate dark chocolate, and weeks later, once after they ate milk chocolate, or vice versa. (This is why it was a test of the immediate effect of chocolate consumption only.)
The upshot is that dark chocolate (dark cocoa) had a positive effect on many of the markers, including the most important one, walking; and milk chocolate did not. The persons in the study were in bad shape to begin with, only able to walk a little more than the length of an American football field (110 meters or 120 yards). After ingesting the dark chocolate (40 grams) the participants, on average, were able to walk 122 meters or 133 yards. If you prefer to think of this in feet, the people increased their walking distance by 40 feet. Also, the time that they could walk before the pain became unbearable was 124 seconds (~ 2 minutes) before the dark chocolate and 142 seconds (20 more seconds) after the dark chocolate. [Important note: the distance and time spent walking was on a treadmill, it is possible that walking off the treadmill, inside or out, would be more difficult.]
Some of the other measures or markers were different after the ingestion of chocolate and some were different depending on the type of chocolate. Of importance, the FMD was different between chocolates, specifically there was more dilation after consumption of the dark chocolate. The chemical tests showed that the dark chocolate itself had more polyphenol content than the milk chocolate and the scientists are suggesting that the antioxidant properties of the polyphenol-rich dark chocolate is responsible for the positive findings.
Yes, this is very cool. Researchers are on the way to finding the means to moderate Intermittent Claudication so that people with PAD can be more active. Of course, an even better thing would be to reduce the number of persons who have PAD. Risks that we have control over include being overweight, smoking, not exercising and having high cholesterol and or diabetes.
I noted in parentheses that the amount of chocolate the patients were given was 40 grams. I assume this was regular chocolate and therefore would contain 200 calories. I assure you that it takes more than 20 seconds of additional walking to burn 200 calories (more like an hour or two).
I do use dark cocoa in cookies and cakes, sweetened with sucralose; I like the taste of cocoa and when added to the antioxidants I consume in my (calorie fixed) plant based diet, I imagine it is health promoting.
*Dark Chocolate Acutely Improves Walking Autonomy in Patients With Peripheral Artery Disease
Lorenzo Loffredo, Ludovica Perri, Elisa Catasca, Pasquale Pignatelli, Monica Brancorsini,
Cristina Nocella, Elena De Falco, Simona Bartimoccia, Giacomo Frati, Roberto Carnevale,
Francesco VioliJ Am Heart Assoc. 2014;3:e001072, originally published July 2, 2014, doi:10.1161/JAHA.114.001072