With the weeks swiftly ticking down to the summer exam season, a poll suggests that many teenagers are already experiencing sleepless nights.

It reveals that in the month leading up to exams, the number of young people getting just five or six hours of sleep doubles, with many admitting that they are kept awake by worry or stress.

The Sleep Council survey, which questioned 1,000 teenagers, found that on a usual night, around one in ten (10.26%) say they get five to six hours of sleep a night.

But in the four weeks before exams start, this rises to one in five (20.62%).

And while just over a quarter (26.39%) say they usually get six to seven hours of shut-eye, this falls to 20.92% in the run up to exams. There are also drops in the proportions that say they get seven to eight, or eight or more hours of sleep a night.

Almost half (48.21%) admitted they have occasionally crammed all of their revision into one night, while a further 7.87% said they always do so.

The findings also show the impact exam season has on young people, with over one in four (27.59%) saying they wake up more frequently due to worrying and stress and a similar proportion (27.69%) say they wake up earlier.

More than a third of those questioned (34%) say they revise for between eight and 10 hours a week for exams while over one in 10 (11%) spend over 14 hours a week on revision.

Lisa Artis, of the Sleep Council, said: "Our research shows that a worryingly high number of teenagers are not getting as much sleep as they need to function and perform at their best in the build up to exams. They are sacrificing sleep to study when in fact they might be more mentally alert cramming in extra sleep rather than more revision.

"There's a growing body of evidence that demonstrates how much the sleep we get impacts on how we perform. A good night's sleep triggers changes in the brain that helps to improve memory, meaning you'll be much better able to remember what you learnt the day before."

:: The Atomik Research survey for the Sleep Council questioned 1,000 13 to 18-year-olds between March 4 and 6.