A Swiss study indicates that the caffeine contained in coffee is not, as was widely thought, responsible for raising blood pressure.

This demonstrates how little we know about the effects of one of our most popular beverages Dr Roberto Corti

Occasional coffee drinkers who drank a triple espresso showed elevated blood pressure - but the same effect was recorded whether or not the drink contained caffeine.

The finding suggests that another ingredient in coffee is to blame for stimulating the cardiovascular system.

The research also indicated that regular coffee drinkers seem to become immune to the effects.

Regular drinkers showed increased stimulation of nerve pathways - but no increase in blood pressure.

Stimulant

Lead researcher Dr Roberto Corti, a cardiologist at University Hospital in Zurich, said: "Our study strongly supports the hypothesis that ingredients other than caffeine are responsible for the stimulating effects of coffee on the cardiovascular system.

"This demonstrates how little we know about the effects of one of our most popular beverages and the most abundantly consumed stimulant worldwide."

The researchers measured blood pressure, heart rate and nervous system activity in 15 healthy volunteers.

Six were habitual coffee drinkers and nine either abstained or drank coffee only occasionally.

The volunteers were given either a full strength triple espresso, a decaffeinated version, an intravenous injection of caffeine or a placebo.

Both types of espresso stimulated a significant jump in blood pressure among those who were not regular coffee drinkers.

Advice

Dr Corti said the lack of blood pressure elevation in coffee drinkers suggested regular consumption may help to reduce its potential for damaging health - at least among people who were not vulnerable to high blood pressure.

Dr Thom said coffee was not the main cause of high blood pressure

He said further research was needed before people with blood pressure problems were advised not to drink decaffeinated coffee.

Professor Bryan Williams, of the Blood Pressure Association, said the study was small and inconclusive.

He said: "Recommendations to reduce or cease coffee consumption in people with hypertension would not be appropriate as it would not make a major impact on blood pressure."

Dr Simon Thom of St Mary's Hospital in London said coffee had a small effect on blood pressure compared to other foods like salt.

"There's absolutely no doubt that lifestyle components and dietary components such as salt have a much far greater influence on blood pressure on a daily basis than small players such as coffee," he said.

The research is published in Circulation: Journal of the American Heart Association.