It has been known for some time that the amount of sleep people get has, on average, declined over the years.

 

We wanted to see what the effect would be of increasing average sleep by just one hour. So we asked seven volunteers, who normally sleep anywhere between six and nine hours, to be studied at the University of Surrey's Sleep Research Centre.

 

The volunteers were randomly¹ allocated²（分派） to two groups. One group was asked to sleep for six-and-a-half hours a night, the other got seven-and-a-half hours. After a week the researchers took blood tests and the volunteers were asked to switch sleep patterns. The group that had been sleeping six-and-a-half hours got an extra hour, the other group slept an hour less.

 

While we were waiting to see what effect this would have, I went to the John Radcliffe hospital in Oxford⁴ to learn more about what actually happens when we sleep.

 

In the Sleep Centre, they fitted me up with a portable electro-encephalograph, a device that measures brain wave activity. Then, feeling slightly ridiculous, I went home and had my seven-and-a-half hours of sleep.

 

Back at the University of Surrey our sleep volunteers had finished their second week of the experiment. What we wanted to see was the effect switching from six-and-a-half hours to seven-and-a-half hours, or vice⁵ versa, would have on our volunteers.

 

Computer tests revealed that most of them struggled with mental agility⁶ tasks when they had less sleep, but the most interesting results came from the blood tests that were run.

 

Dr Simon Archer³ and his team at Surrey University were particularly interested in looking at the genes⁷ that were switched on or off in our volunteers by changes in the amount that we had made them sleep.

 

"We found that overall there were around 500 genes that were affected," Archer explained. "Some which were going up, and some which were going down."

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