They found that boys who had more than the recommended maximum two hours of 'screen time' a day were far more susceptible to developing insulin resistance, a precursor to type-2 diabetes.
The survey found an alarming 90 per cent of boys and 75 per cent of girls exceeded the two-hour guideline.
Hardy said that surveyed teens spent a total of almost 22 hours glued to their televisions and computers every week.
While boys were the worst offenders, Hardy said girls were catching up.
"Girls have started to adopt screen technology, particularly Facebook and blogging," the Daily Telegraph quoted her as saying.
Hardy will present her findings next week at the International Congress of Obesity in Sweden.