Dark chocolate does something that we all felt but couldn't confirm.
Dark Chocolate could reduce stress, improve memory and mood - short science articles

Consumption of dark chocolate with a high concentration of cacao might have a positive impact on mood, stress as well as immunity. Cacao is an important source of flavonoids and for the first time, its effects have been studied in humans to support cognitive, endocrine and cardiovascular health. These flavonoids have potent anti-oxidants and also anti-inflammatory properties which are considered to be responsible for this effect. Scientists are carrying out further research to understand the mechanism for the cause-effect relationship between brain and behaviour.

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Scientific publication: FASEB journal
Scientific publication: FASEB journal