The study, led by neurophysiologist Dr David Lewis, tested a group of six couples in their twenties and discovered volunteers reacted more strongly to chocolate than their partner's kiss. Heartbeats per minute more than doubled in some cases - increasing from a resting rate of 60 to 140. In addition, the buzz from the taste of chocolate produced a more sustained reaction with volunteers feeling the effects up to four times longer than those generated by a kiss. Participants tasted a piece of dark chocolate, provided by confectionery giant Cadbury, and the surprising response was noted equally in men and women. Chocolate's feelgood factor is widely recognised by consumers and the product has been linked to the released of serotonin in the brain - an action which produces feelings of pleasure. Nevertheless, researchers expressed surprise at the findings. Dr Lewis said: "These results really surprised and intrigued us. While we fully expected chocolate - especially dark chocolate - to increase heart rates due to the fact it contains some highly stimulating substances, both the length of the increase together with the powerful effects it had on the mind were something none of us had anticipated." Dark chocolate has become so popular, due in part to the extensive coverage of its health benefits, that it now accounts for 19 per cent of global chocolate sales and is set to continue growing as a sector. According to a study from cocoa processor Barry Callebaut, France is the leading consumer of dark chocolate with 57 per cent of respondents reporting its use compared to 47 per cent in Belgium, 40 per cent of Swiss, 7 per cent of Germans, and 35 per cent of Brits.