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.
Dr Michael Mosley takes part in a sleep study
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根据英国睡眠委员会（的调查），英国人平均每晚睡6.5个小时。米歇尔·莫斯利参与了一次不同寻常的实验，以确认（6.5小时的睡眠）是否足够。——
米歇尔·莫斯利 2013. 10.9
多年来，人们的平均睡眠时间在缩短。这已不是什么新鲜事儿了。
发生这样的情况，原因有很多。尤其在如今的生活环境中，人们倾向于将睡眠当成一种奢侈——睡眠（时间）是可以被轻易减短的。归根结底，这体现了咖啡因的作用——把你从睡眠世界震醒。一方面我们的睡眠平均时长在下降，而另一方面，肥胖和糖尿病的（发病率）却大幅上升。这两者之间有关联吗？
我们想知道在平均睡眠时长上延长一小时会带来什么影响。所以邀请了7位平均每晚睡6-9个小时的志愿者，在（英国）萨里大学的睡眠研究中心参与研究。
志愿者们被随机分为两组。一组每晚睡6.5小时，另一组每晚睡7.5小时。如此进行一周之后，研究人员对志愿者进行了验血。（之后） 两组交换睡眠模式。睡6.5小时的那组志愿者多睡一小时，而睡7.5小时的那组则少睡一小时。
在等待此番安排产生的结果时，我到牛津大学的约翰瑞德克里夫医院去了解我们睡觉时究竟发生了什么。
在睡眠（研究）中心，他们让我戴上了便携式脑电图自动记录仪，以记录脑电波的活动。然后，带着有些奇怪的感觉 ，我回到家中，开始了七个半小时的睡眠。
第二天我和凯瑟琳· 伍尔夫博士讨论了前一天晚上在我大脑中发生的情况。
她指出的第一件事就是，我很快进入了深度睡眠状态。深度睡眠听上去带给人休息，但实际上在此状态下，（我们的）大脑却在辛勤地工作。大脑做的工作之一就是把短期记忆移入长期记忆储存区，使我们在第二天能够记下更多的短期记忆。如果你的深度睡眠不足，那么这些（当天的短期）记忆就会丢失。
你可能会认为：“工作日我减少的睡眠可以在周末弥补回来。”不幸的是，记忆的工作模式并非如此，它需要在形成的24小时内加以巩固。
正因为睡眠对巩固记忆非常重要，你最好改变（你的睡眠模式），或者参加一项测试以确定你的晚间睡眠（时长）是合理的。一项研究表明，晚间睡眠不合理者的记忆力比其他人差40%。
深度睡眠只持续几小时。我的脑电波显示出，在晚间，我的大脑经历了另一种（类型的）睡眠阶段——快速眼动睡眠阶段，且经历了多次。
“在这一阶段，你（的身体）通常是麻痹的——所以你动不了。”伍尔夫解释道。“事实上（在此阶段）唯一没有麻痹的是（你的）眼部肌肉，所以该阶段被称为快速眼动阶段。”
在快速眼动阶段发生了许多离奇的事情。降肾上腺素，大脑中的一种与压力相关的化学物质（的活动）被抑制了。这是一天中，这种化学元素唯一被抑制的时段。这使得我们的（身体）保持平静，（与此同时我们的）大脑则对白天的经历进行再加工，帮助我们接受那些事件，尤其是情绪化的事件。
快速眼动阶段多发生在后半夜。这意味着，如果你忽然醒来，你的大脑尚未完全处理好你的情绪——而你会感到有压力，很焦躁不安。深夜喝酒不好，酒精在你身体内会导致快速眼动睡眠缩短。
米歇尔·莫斯利博士参与的一项睡眠研究。
西蒙·阿彻博士和他萨里大学的团队对观察以下问题特别感兴趣：睡眠时长的变化会怎样影响志愿者的基因——它们在什么时候起作用，在什时候受抑制。计算机测试显示出，大多数志愿者在睡眠缺乏时需要更加努力才能完成对精神灵敏度要求高的任务。然而最有趣的（研究）结果来自于他们的验血报告。
“我们发现一共有500个基因受到影响，” 阿彻解释道，“有些变活跃了，有些则受到抑制。”
他们发现，当志愿者们从每晚7.5小时的睡眠减少到每晚睡6.5小时，（他们体内的）与发炎、免疫反应与压力反应相关的基因变得更活跃。（研究）小组还发现，（在志愿者体内）与糖尿病、癌症风险相关的基因也变得更活跃了。而当志愿者们增加一小时睡眠时，情况则刚好相反。
所以，这个实验传达了明确的信息：每晚睡眠少于7小时的你若愿意改变睡眠习惯，即使是一丁点儿的改变，也能变得更为健康。“睡个懒觉，对你有好处。”——这样的信息并不常被人提及。
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