Washington : Popular energy drinks promise superior athletic performance and weight loss, a new study says.

"Most of the performance-enhancing effects of energy drinks can be linked to their caffeine content," says Stephanie Ballard, the study leader and assistant professor of pharmacy at the Nova Southeastern University's West Palm Beach campus in the US.

"Caffeine has been consistently observed to enhance aerobic performance," says Ballard, who co-authored the report with colleagues, reports the journal The Physician and Sportsmedicine.

"Caffeine has (also) been reported to cause insomnia, nervousness, arrhythmias (erratic heartbeats), osteoporosis, cardiovascular disease, pregnancy and childbirth complications, gastrointestinal upset and death," adds Ballard, according to a report.

Don't forget these drinks are often loaded with sugar, Ballard adds. "Despite their use for weight loss, energy drinks may be contributing to the obesity epidemic alongside less caffeinated, sugary drinks like soda."