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The average Briton gets six-and-a-half hours' sleep a night, according to the Sleep Council. Michael Mosley took part in an unusual experiment to see if this is enough.

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

This has happened for a whole range of reasons, not least because we live in a culture where people are encouraged to think of sleep as a luxury - something you can easily cut back on. After all, that's what caffeine is for - to jolt you back into life. But while the average amount of sleep we are getting has fallen, rates of obesity and diabetes have soared. Could the two be connected?

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 randomly allocated 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 Oxford 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.

The following day I went to discuss what had happened inside my head during the night with Dr Katharina Wulff.

The first thing she pointed out was that I had very rapidly fallen into a state of deep sleep. Deep sleep sounds restful, but during it our brains are actually working hard. One of the main things the brain is doing is moving memories from short-term storage into long-term storage, allowing us more short-term memory space for the next day. If you don't get adequate deep sleep then these memories will be lost.

You might think: "I'll cut back during the week and then make up for it at the weekend." Unfortunately it doesn't work like that, because memories need to be consolidated within 24 hours of being formed.

Since deep sleep is so important for consolidating memories it is a good idea if you are revising or perhaps taking an exam to make sure that you're getting a reasonable night's sleep. In one study, people who failed to do so did 40% worse than their contemporaries.

Deep sleep only lasts for a few hours. My electrode results showed that during the night my brain went through multiple phases of another kind of activity, called REM sleep.

"This is the phase when you are usually paralysed - so you can't move," Wulff explained. But the eye muscles are not paralysed, and that's why it's called rapid eye movement sleep."

During REM sleep an extraordinary thing happens. One of the stress-related chemicals in the brain, noradrenalin, is switched off. It's the only time, day or night, this happens. It allows us to remain calm while our brains reprocess all the experiences of the day, helping us come to terms with particularly emotional events.

We get more REM sleep in the last half of the night. Which means that if you are woken unexpectedly, your brain may not have dealt with all your emotions - which could leave you stressed and anxious. Drinking alcohol late at night is not a good idea as it reduces your REM sleep while it's being processed in your body.

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 vice versa, would have on our volunteers.

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

Dr Simon Archer and his team at Surrey University were particularly interested in looking at the genes 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."

What they discovered is that 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.

So the clear message from this experiment was that if you are getting less than seven hours' sleep a night and can alter your sleep habits, even just a little bit, it could make you healthier. "Have a lie-in, it will do you good" - that's the kind of health message that doesn't come along very often.

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據(jù)英國睡眠委員會（Sleep Council）調(diào)查顯示，英國人平均每天只睡6.5小時。為了驗(yàn)證這樣的睡眠是否足夠，邁克爾·莫斯利醫(yī)生（Michael Mosley）參加了一項(xiàng)不尋常的實(shí)驗(yàn)。

近些年來，人們已經(jīng)認(rèn)識到了這樣的事實(shí)：我們的平均睡眠時間正在逐漸減少。

這一現(xiàn)象的原因是多方面的，其中之一便是我們所處的文化讓我們覺得睡覺是件奢侈的事情，可以輕而易舉地縮減。畢竟，咖啡因的功能就在這兒了：把你喚回清醒的狀態(tài)。然而，隨著睡眠量的不斷下降，肥胖和糖尿病的發(fā)病率卻在大幅升高——二者之間會不會有一定關(guān)系呢？

我們想看看把平均睡眠時間增加一小時會有什么效果，于是邀請了7位志愿者參加我們的實(shí)驗(yàn)。這7個人平日的睡眠在6—9個小時之間。實(shí)驗(yàn)由薩里大學(xué)（University of Surrey）的睡眠研究中心負(fù)責(zé)主持。

我們將志愿者隨機(jī)分為兩組，一組每晚睡6.5小時，另一組睡7.5小時。一周之后研究者對兩組人的血液進(jìn)行檢測，并調(diào)換兩組的睡眠量，原來睡6.5小時的一組多睡一小時，另一組則少睡一小時。

就在我們等待實(shí)驗(yàn)結(jié)果的過程中，我來到位于牛津的約翰·拉德克里夫醫(yī)院（John Radcliffe hospital），看看我們睡覺時究竟發(fā)生了什么。

在該院的睡眠中心里，工作人員為我戴上一臺便攜式腦電圖儀。就這樣，我戴著儀器半覺好笑地回到家，睡了7.5個小時。

第二天，我來到醫(yī)院，向卡塔琳娜·伍爾夫醫(yī)生詢問了我的情況。

首先，她指出我很快就進(jìn)入了深睡眠。雖然聽上去挺安詳，大腦在深睡眠時其實(shí)在積極地工作，其中一件重要的事情便是將短期記憶轉(zhuǎn)存到長期記憶中，從而為第二天的短期記憶騰出空間。如果睡得不夠，一些短期記憶便會丟失。

你也許會想：“我在工作日里縮減睡眠，到周末再補(bǔ)上不就行了嗎？” 遺憾的是，大腦的運(yùn)行機(jī)制并非如此，因?yàn)橛洃浶枰谧畛跣纬傻?4小時內(nèi)得到強(qiáng)化。

由于深睡眠對于強(qiáng)化記憶十分重要，復(fù)習(xí)和考試前睡夠覺就很有必要。在一項(xiàng)研究中，那些在復(fù)習(xí)和考試前沒能睡夠覺的學(xué)生比同齡人表現(xiàn)差了40%。

深睡眠只能持續(xù)幾個小時。我的腦電圖顯示，大腦在夜里經(jīng)歷了幾個稱為快速動眼睡眠（REM）的階段。

“人處于這一階段時通常是麻痹的，所以動不了。”伍爾夫解釋道。但由于這時的眼部肌肉并未麻痹，因此這一階段的睡眠稱作“快速動眼睡眠”。

快速動眼睡眠時，我們的體內(nèi)會發(fā)生一種奇特的變化：腦內(nèi)的去甲腎上腺素（一種與壓力有關(guān)的化學(xué)物質(zhì)）會大量消失，使得我們能夠在平靜中對白天的經(jīng)歷進(jìn)行再加工，從而更好地應(yīng)對某些事件對我們造成的情緒影響。然而，無論黑夜還是白天，去甲腎上腺素只有在快速動眼睡眠中才能大量消失。

由于快速動眼睡眠更多地分布于后半夜，如果你在夜里突然醒來，大腦這時很有可能還沒完全處理掉你的情緒，從而導(dǎo)致壓力感和焦慮的產(chǎn)生。深夜飲酒可不是什么好事情，因?yàn)榇x酒精會縮短快速動眼睡眠的時間。

兩周后，我們的睡眠志愿者們結(jié)束了實(shí)驗(yàn)。我們想看看，人在少睡一小時和多睡一小時時會有哪些變化。

計算機(jī)測試結(jié)果表明，少睡一個小時時，多數(shù)人在完成思維敏捷性的任務(wù)時顯得力不從心。不過更有趣的還是血液的檢測結(jié)果。

薩里大學(xué)的西蒙·阿徹博士和他的團(tuán)隊(duì)發(fā)現(xiàn)，睡眠時間的變化會影響基因的活躍程度。

“我們發(fā)現(xiàn)一共約有500個基因受到影響�！卑卣f。“有些變得更加活躍，有些則相反�！�

他們發(fā)現(xiàn)，當(dāng)志愿者的睡眠從7.5小時減少到6.5小時時，體內(nèi)與炎癥、免疫和應(yīng)對壓力相關(guān)的基因變得更加活躍，與糖尿病和癌癥相關(guān)的基因也是如此。而當(dāng)受試者的睡眠時間增加后，這些基因的活躍程度便減弱了。

因此，實(shí)驗(yàn)清楚地表明，對于那些睡不夠7個小時的人而言，如果他們能夠改變睡眠習(xí)慣，哪怕只是做出一點(diǎn)點(diǎn)改變，他們的身體都會變得更健康。“多睡會吧，對你有好處�！边z憾的是，這樣的建議我們聽到的太少了。