CANBERRA (Reuters) - Just one can of the popular stimulant energy drink Red Bull can increase the risk of MI or stroke, even in young people, Australian medical researchers said on Friday. The caffeine-loaded beverage, popular with university students and adrenaline sport fans to give them "wings", increased blood viscosity.

Scott Willoughby and colleagues tested the cardiovascular systems of 30 young adults one hour before and one hour after consuming one 250-ml can of sugar-free Red Bull. The results showed "normal people develop symptoms normally associated with cardiovascular disease" after consuming the drink, created in the 1980s by Austrian entrepreneur Dietrich Mateschitz based on a similar Thai energy drink.

"One hour after they drank Red Bull, (their blood systems) were no longer normal. They were abnormal like we would expect in a patient with cardiovascular disease," Willoughby, lead researcher from the Cardiovascular Research Centre at the Royal Adelaide Hospital, told the Australian newspaper.

Red Bull Australia spokeswoman Linda Rychter said the report would be assessed by the company's head office in Austria. "The study does not show effects which would go beyond that of drinking a cup of coffee. Therefore, the reported results were to be expected and lie within the normal physiological range," Rychter told Reuters.

Red Bull is banned in Norway, Uruguay, and Denmark because of health risks listed on its cans, but the company last year sold 3.5 billion cans in 143 countries. One can contains 80 mg of caffeine, around the same as a normal cup of brewed coffee.

The Austria-based company, whose marketing says "Red Bull gives you wings", sponsors Formula 1 race cars and extreme sport events around the world, but warns consumers not to drink more than two cans a day. Rychter said Red Bull could only have such global sales because health authorities across the world had concluded the drink was safe to consume.

But Willoughby said Red Bull could be deadly when combined with stress or high blood pressure, impairing proper blood vessel function and possibly lifting the risk of blood clotting. "If you have any predisposition to cardiovascular disease, I'd think twice about drinking it," he said.

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