Reference
Wirtz PH, von Känel R, Meister RE, et al. Dark chocolate intake buffers stress reactivity in humans. J Am Coll Cardiol. 2014;63(21):2297-2299.
Design
This was a placebo-controlled, single-blind study involving healthy, nonsmoking men aged 20 to 50 years (mean±standard deviation: 35.7±8.8) who were not taking any medication. Participants were assigned to receive either dark chocolate (n=31) or placebo (n=34). The dark chocolate used was 72% cacao and contained 281 calories and 125 mg of the flavanol epicatechin per 50-g serving. The placebo looked and tasted identical but was actually a flavanol-free white chocolate that was dyed and flavored to match the color, appearance, and smell of the dark chocolate. For 48 hours before ingestion of the chocolate, participants did not participate in strenuous physical activity and also did not consume substances that contained dark polyphenols, milk, milk-containing products, coffee, or alcohol. They drank only water 2 hours before the experiment.
Outcome Measures
Two hours after chocolate ingestion, both groups underwent an acute stressful situation that included a standardized psychosocial stress task combining public speaking and mental arithmetic. Measurements of the stress hormones were taken before ingestion and several times after the stress task. These hormones included plasma adrenocorticotropic hormone, epinephrine, norepinephrine, and epicatechin, as well as salivary cortisol levels.
Key Findings
The dark chocolate group had significantly blunted cortisol (P<0.001) and epinephrine (P=0.021) reactivity to the psychosocial stress compared to placebo. Results were not significantly impacted when controlled for age, body mass index, and mean arterial blood pressure. Epicatechin plasma levels were elevated in the intervention group.
Practice Implications
The cardiovascular benefits of dark chocolate have been confirmed. As indicated by a 2009 literature review, cocoa polyphenols improve endothelial function, reduce platelet aggregation, balance blood sugar, improve insulin sensitivity, and help control blood lipids.1 This is the first study to demonstrate efficacy associated with the stress response in humans.
In 2011, researchers demonstrated that epicatechins do, in fact, cross the blood-brain barrier.2 It has been unclear whether or not the levels can be significant enough to affect central nervous system pathophysiology. This study clearly shows that a single dose of flavonoid-rich dark chocolate can buffer endocrine reactivity to stress, thereby helping to protect the body from the damages associated with acute stress in healthy individuals.
While this study only measured plasma epicatechin content, it is likely that the other flavanols in cocoa may be contributing to the stress-protective effects as well.3 From a clinical perspective, the cardiovascular benefits associated with chocolate flavanol consumption make it an appealing recommendation for patients, especially those at high risk of cardiovascular disease.4 Patients experiencing acute episodes of stress, potentially a large portion of most clinical practice cases, will likely receive additional benefit from consuming about 2 oz of dark chocolate daily.
