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Old people are known to be lousy sleepers, but a new study suggests it might all be in their heads, at least for many of them.

Medications, poor health, bad bedtime habits (such as watching a movie or drinking coffee or booze), circadian rhythms, and too much or too little in their personal "sleep bank" have all taken the blame for seniors' common complaints of insomnia.

Elizabeth Klerman of Brigham and Women's Hospital and the Harvard Medical School set out to clear it up once and for all with a controlled study of 18 subjects ages 60 to 76 and 35 younger subjects, ages 18 to 32, all healthy and not on medication that might affect sleep. Even people who had crossed more than one time zone in the past 3 months were disqualified, as well as those who had worked night or rotating shifts in the past three years.

After monitoring their sleep at home, the subjects were regularly instructed to lie quietly with their eyes closed and to try to sleep, for as much as 16 hours daily for several days in a row. They had all the time in the world.

The bottom line was that the seniors simply needed less sleep — about 1.5 hours less.

Circadian rhythms and preferences

The results are detailed online in the July 24 issue of the journal Current Biology. Younger subjects slept for an average of 9 hours compared to 7.5 for older people, said Klerman and her colleague Derk-Jan Dijk of the Surrey Sleep Research Centre in England.

The age-related decline in sleep included an even split between rapid eye movement (REM) sleep, associated with dreaming, and non-REM sleep, Klerman said.

Klerman and Dijk kept subjects in conditions that controlled for circadian rhythms by allowing the chance to sleep during both the night and the day and by controlling individual choices in sleep opportunities.

While humans sometimes cannot sleep when tired, there is no evidence that they can sleep when they are not tired, Klerman explained.

Insomnia and expectations

The results have implications for seniors who think they have insomnia.

"There are definitely older people with insomnia," Klerman told LiveScience. "However there may also be some older people who 'create' insomnia if they believe that they 'need' 8 to 9 hours of sleep and therefore spend more time in bed (lying awake) than needed to achieve the amount of sleep 'needed.'"

"It's also possible that they sleep less even when given the opportunity for more sleep because of age-related changes in the ability to fall asleep and remain asleep," she added, noting that the new results apply only to healthy individuals taking no medication and having no medical conditions or sleep disorders.

The study also found that most healthy people, and young people in particular, don't get as much sleep as they need.

Given the evidence that insufficient sleep is associated with increased risk of accidents, errors, decreased learning and immune function, and metabolic changes similar to diabetes, Klerman encouraged younger people to sleep more than they currently do.

Ages of sleep

The idea that our sleep habits change markedly across the life span isn't new.

The same study found another age effect: Given the same amount of time in bed, older people take longer to fall asleep.

The researchers set 60 years old as the starting point for their older subjects to ensure a clear distinction from the younger group, but it is possible that the declining capacity to sleep could reach back into the middle-age years too, Klerman said.

"My expectation is that the change is gradual and there is no time point at which we 'age,'" she said. "Sleep changes from infancy, through childhood, puberty, young adulthood and middle-age until we die."

Needless medications?

The findings may also influence treatment for insomnia in older people and provoke novel approaches, such as exercise, new pharmaceuticals or ocular light therapy, Klerman said.

"If older people believe that they need more sleep than they can achieve even when they spend extra time in bed, then they may complain of insomnia: being awake when wanting to be asleep. They may start using medications needlessly," Klerman said.

However, if seniors are tired during the day, they should consider an evaluation for a sleep disorder that may be interfering with their ability to obtain good sleep at night.

The research was funded by the National Institutes of Health. Dijk is supported by the Biotechnology and Biological Sciences Research Council of the United Kingdom and Wellcome Trust.

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老年人是众所周知的睡眠糟糕的人群，但是一项新的研究却说这都可能是因为他们脑部活动的原因，至少他们当中很多人如此。

药物治疗、健康状况差，不好的就寝习惯（如睡觉前看电影或喝咖啡、喝酒）、昼夜生理节奏和个人本身或多或少“睡眠库”都是让年龄大的人抱怨失眠的主因。

百翰女子医院的伊丽莎白 凯勒曼和牛津医药学校一起开始弄清真相并且做了一项严格控制的研究，他们找了18个年龄在60-76岁的实验对象和35个年轻的实验对象，年龄在18-32岁之间，所有的实验对象都身体健康，没有服用过影响睡眠的药物，甚至曾经在过去的3个月里跨过一个时区的人都不适合参加此研究试验，还有那些在过去3年里夜里工作或工作连轴转的人也不行。

在检测到他们在家睡眠后，这些实验对象被规律地引导去静静地躺下，闭上眼睛努力睡去，一个接一个连续几天都尽可能多地达到每天睡16小时，他们拥有世界上所有的时间。

根本原因是上年纪的人只需更少的睡眠——大约少了1.5小时。

昼夜胜利节奏&喜好

一本名叫《当前生物学》的7月24日刊在线详细阐述了试验结论。科勒曼与他的合作伙伴——英格兰萨利睡眠中心的德克 詹 迪耶克说，比起老人平均睡眠7.5小时这个数字，年轻的实验对象们平均每天睡9小时。

科勒曼说，年龄相关的睡眠下降包括一种均衡的区分，这种区分发生在眼球快速活动（REM）睡眠和眼球非快速活动（REM）睡眠之间，前者跟做梦有关系。

科勒曼和迪耶克令实验对象们处于一种为昼夜生理节奏而控制的条件中，在黑夜和白昼中都允许有睡眠的时间，而且在他们睡眠来临时监控个人的睡眠选择时间。

科勒曼说，而人有时在太累的情况下睡不着，却没有证据证明他们在不累的时候可以睡着。

失眠和期盼

结果暗示是老年人以为他们失眠。

科勒曼在生活科学栏目告诉我们：“确实有老年人失眠，可是有些老年人如果坚信他们需要8-9小时睡眠，因此他们会躺在床上睡觉耗费更多时间（醒着躺在床上），这比他们需要达到的实际睡眠时间也更长，这也就产生了他们所谓的“失眠”。

科勒曼又补充道：“也有可能由于年龄的变化可以入睡或是处于睡眠状态，而有了更多睡眠的机会，他们却睡得少了。”需要注意的是，这个新的调查结果只用于那些健康人，他们没有经过药物治疗，没有用药或是睡眠紊乱。

研究还发现最健康的人，尤其是年轻人达不到他们这个年龄需要的睡眠量。

有证据证明睡眠不足与剧增的危机、误差、认知不足和免疫系统功能，和类似于糖尿病的新陈代谢病变有关。科勒曼鼓励年轻人要睡得比他们目前的睡眠时间长些。

睡眠年龄

经过生命周期后我们的睡眠习惯显著改变这一说法不再新颖了。

同样的研究发现另一个年龄影响：同样的睡眠时间，老人往往要花费更多的时间才能睡着。

研究人员将60岁设为一个老年实验对象的年龄起点，以此保证与年轻实验对象有显著的特征，但是科勒曼说也有可能下降的睡眠量也会达到中年的岁数。

她说：“我希望这种变化是循序渐进的，而且没有时间指出我们处于哪个年龄段，睡眠的变化从婴幼儿期开始，经过儿童期、青春期、青年期和中年期知道我们死亡。”

不必要的药物治疗？

科勒曼说，这些发现也有可能影响老年人对失眠的治疗，还有就是产生神奇的效果，如锻炼、新的药物配方，或是眼睛光线的治疗。

她还说：“如果老年人相信比起他们用更多的时间用于睡觉可以达到睡眠时间，他们需要更多的睡眠，那么他们可能会抱怨自己失眠：想睡觉却睡不着。他们可能开始使用没必要的药物治疗。”

尽管如此，一天下来老年人也很累，他们里应该考虑睡眠紊乱的原因，这个可能就是妨碍他们在夜晚能有个好眠的原因。

此项研究有国家健康协会提供资金资助，迪耶克由英国生物技术和生物科学研究委员会以及威尔卡姆信托基金资助。