18 April 2012 Last updated at 08:30 ET

Clock change could leave teenagers more sleepy

Not enough sleep can affect teenagers' school work

Teenagers can suffer severe sleep deprivation when the clocks change, say researchers at the University of Surrey.

The amount they sleep decreases to less than six hours a night on average the week following the move to British Summer Time.

During this period their concentration may be lower and mood affected.

Scientists also found that even before the change, teenagers were getting less than the recommended hours of sleep.

The activity of some sixth-form students from Claremont Fan Court School in Surrey was studied using wristwatches.

These were worn constantly over a 10-day period before and after the clocks moved forward on 25 March.

The watches reliably indicated when the teenagers were awake and asleep.

The researchers found that in the days following the clock change, the teenagers had less than six hours of sleep a night. Adults generally have eight.

Delayed sleep hormones

Joanne Bower, a sleep researcher at the University of Surrey said: "During adolescence, teenagers experience a shift in their circadian rhythm [body clock] - these make sure the same things happen at the same time every day. One of these things is the production of the sleep-promoting hormone, melatonin.

"For an adult, you would expect that to be early evening, but in teenagers it happens much later.

"Even if you put your teenager to bed at 10 at night, they may not secrete melatonin until midnight, and so they're staring at the ceiling, and aren't sleepy.

"This means teenagers are awake later in the evening and find it difficult to rise early in the morning.

"Add this to the clock change, in which we lose an hour of sleep, and teenagers may suffer more than most."

The need for more sleep is something teenagers are familiar with. Noelle Delaney, a mother of a student involved in the study, said: "Some days it can be very difficult. I have been known to go in and pull her by her feet out of bed."

Consistent sleep deprivation can affect your health.

Mrs Bower said: "With anyone who doesn't get enough sleep it can be quite concerning. Over the long term you can find problems with your performance, concentration, and mood. We're lucky we are quite resilient. I think people generally do have an amazing ability to bounce back."

As this study was small, nine students in total, Mrs Bower says further research is needed.

"It would be good to have a bigger study looking at more teenagers. In this study we tested student performance the day before and after the clock change. It would be good to look at this during the days running up to and after the clock change and at different times of day."