
The University of Surrey's Sleep Research Centre studied the effect of increasing average sleep by just one hour. They took forteen volunteers, who normally sleep anywhere between six and nine hours, and randomly allocated them 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, while the other group slept an hour less.
The John Radcliffe hospital in Oxford revealed what actually happens during sleep. At first, a preson experiences deep sleep. This sounds restful, but during those few hours the brain is working hard. One of the main things to happen is the brain moves memories from short-term storage into long-term storage, allowing more short-term memory space for the next day. If adequate deep sleep isn't achieved, these memories are lost. A person can't make up for lost sleep, because these memories will be lost.
This storage sounds remarkably similar to a computer program when you don't click 'save'.

Drinking alcohol late at night is not a good idea as it reduces your REM sleep while it's being processed in your body. Well. Nothing new there. But some people refuse to listen to good advice.
After the sleep volunteers finished their second week of the experiment at the University of Surrey, the results of switching sleep times were astounding. When the volunteers cut back from seven-and-a-half to six-and-a-half hours' sleep a night, genes that are associated with processes like inflammation, immune response and response to stress became more active. The team also saw increases in the activity of genes associated with diabetes and risk of cancer. The reverse happened when the volunteers added an hour of sleep.

I'm lucky to sleep well. I get 8 hours a night, rarely varying the amount. I wake refreshed and eager to get on with my day. How about you?