This study in The American Journal of Medicine says “yes”. http://www.amjmed.com/article/S0002-9343%2809%2900874-2/abstract.
The study showed that when healthy young adults were tested one hour after consuming one 250ml can of a sugar-free energy drink, their endothelial function decreased and platelet aggregation increased. What does that mean? It means that the inner lining of their blood vessel walls became less functional and that their red blood cells started to stick together more. Bad on both counts. Both of these things increase your risk of heart attacks.
Take note that this study was done on healthy young adults. Imagine unhealthy or older adults who have generally have poorer cardiovascular function. And, this was with just one can of an energy drink. I know people who consume more than one in a day. And, people who consume these drinks regularly.
Some energy drinks claim to be healthy. “Sugar-free”. So, what’s in there to sweeten it? “No caffeine”. No extra caffeine added or does is there guarana in there (note that guarana contains caffeine)? What other energy-promoting substances are added then? Some may be healthy. Some may not be. Some may be good for some, but not for you. We’re all different.
Think about it…why do you need an energy drink? Are you getting enough sleep? Is your sleep of good quality? Are you actually really bored? Dehydrated? Undernourished? Over doing it?