Results of a stress test after subjecting study participants to a mock job interview and a mental arithmetic task in front of an audience indicated that consumption of dark chocolate blunted increases in cortisol and epinephrine.
Scientists from the University of Bern and the University of Zurich report their findings in the Journal of the American College of Cardiology.
Food giants like Nestle are known to be researching this field, and scientists from the Swiss company have already published several papers on this topic. A 2009 study published in the Journal of Proteome Research indicated that consuming 40 g of dark chocolate per day for two weeks led to reductions in the stress hormone cortisol and catecholamines.
Barry Callebaut have also funded studies in this area, with results of a 2013 randomized, double-blind study by scientists from the Swinburne University of Technology in Australia indicating that cocoa flavanols may keep you calmer and content without affecting cognitive performance (Journal of Psychopharmacology, Vol. 27, pp. 451-458).
The benefits are linked to the flavanols in cocoa, a class of polyphenols, and particularly the monomeric flavanol (-) epicatechin.
According to a 2003 analysis by the US Department of Agriculture (USDA), a typical 100 g bar of dark chocolate contains 41.50 mg of epicatechin and 11.99 mg of catechin. The same amount of milk chocolate contains an average of 10.45 mg of epicatechin and 2.90 mg of catechin.