How much sleep do we need?
Dan Cossins interviews Prof Jim Horne, Director of Loughborough University's sleep research centre to find out if 40 winks is enough...
Do we get enough sleep?
We are obsessed with the amount of sleep we get nowadays, and whether we get enough. Some say that we slept longer in the past, but most people had awful sleeping conditions until about 100 years ago. Circumstances today are much better, and most of us actually sleep very well. Between seven and eight hours a night is probably optimal.
Are current sleeping patterns ‘normal’?
Actually, confining sleep to one block in the night is probably not normal. Two sleeping periods a day was a very common practice throughout much of the world, and still is. People in Mediterranean countries have siestas which last several hours, so they only need to sleep four to five hours in the night and can stay up later. Medieval Europeans had what was called a ‘fyrste sleep’ at about six o’ clock in the evening, for about an hour, so they’d feel refreshed for any social activities taking place later on.
Can an afternoon nap be beneficial?
It can be useful, but only under the right circumstances. If you’re fully alert, a nap is pointless, but if you’re feeling sleepy, it can overcome that and be very refreshing. A nap should be kept short – no more than 20 minutes – otherwise it could develop into full-blown sleep, and you’ll feel groggy when you wake up, like you’re suffering from jet lag.
What is ‘sleep debt’?
It’s a term that implies that we have something to pay off. You can make up for lost sleep very quickly, with only a small return of what you’ve lost. If you normally sleep for seven hours, and miss a night, 10 hours the next night should do the trick. You only need to make up the deep sleep you’ve lost – light sleep and REM sleep can be forfeited.
What has brain-scanning technology taught us about sleep?
Functional MRI has shown us a bit about what parts of the brain are involved in sleep, but these techniques only get down to a resolution of about one cubic millimetre, or roughly 10,000 neurones. To really understand sleep, we need to get down to the cellular level. ‘Neuroglial cells’ probably have a lot to do with it, but we still don’t know much about them.