A team from Hull York Medical School found in a pilot study that patients experienced less fatigue after having dark chocolate with high cocoa content than with white chocolate dyed brown, the BBC reported.

They said the results were surprising but dark chocolate may be having an effect on the brain chemical serotonin.

Chronic fatigue syndrome has a range of symptoms but is particularly characterised by profound muscle fatigue after physical exertion.

Study leader Steve Atkin said the idea for the study came after a patient reported feeling much better after swopping her normal milk chocolate for dark chocolate with a high cocoa content.