High energy drinks raise heart rate and blood pressure

They contain chemicals including caffeine and taurine, an amino acid, that stoke up alertness but are potentially harmful to those with heart conditions.

A study in Detroit has found they can even harm consumers who are simply sitting still.

Dr James Kalus, of the Henry Ford Hospital, said: "We saw increases in both blood pressure and heart rate in healthy volunteers who were watching movies. They were just in a resting state."

The change did not rise to dangerous levels among the healthy volunteers, whose average age was 26, he said.

But it could be significant in people with cardiovascular disease or those taking drugs to lower heart rate or blood pressure.

The participants drank two cans of energy drinks daily over seven days.

Each can contained 80 milligrams of caffeine and 1,000 milligrams of taurine.

Their heart rates rose by about 8 per cent on the first day and 11 per cent on the seventh day.

Sara Stanner of the British Heart Foundation said caffeine should not have a major effect.

"Regular physical activity, a diet low in saturated fat and one that includes five portions of fruit and veg a day are more likely to help protect our hearts than the amount of caffeine we drink," she added.