Go easy on the big energy drinks

In a trial with healthy volunteers, drinking 32 ounces of energy drink (just under a litre) within an hour changed the heart's electrical timing more than a dummy drink did. A measure called QTc, how long the heart takes to recharge between beats, went up by about 6 to 8 milliseconds. Blood pressure went up too. Evidence: decent

These were short-term measures, taken in the hours after drinking. The study didn't look at long-term harm. It does show the heart working differently after a big dose, in people with nothing wrong with their hearts. Evidence: decent The dummy drink had no caffeine and the energy drinks had about 300 milligrams, three or four coffees' worth, so this study can't say how much was the caffeine and how much the rest.

If you have a heart condition or high blood pressure, or you take stimulant medication, like the kind prescribed for ADHD, leave energy drinks alone. Don't stack one on top of other caffeine: coffee, caffeine tablets, another can.

A dose that size is about four ordinary cans. What one small can does on its own, this study can't say. Evidence: worth trying