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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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老年人是眾所周知的睡眠糟糕的人群，但是一項(xiàng)新的研究卻說這都可能是因?yàn)樗麄兡X部活動(dòng)的原因，至少他們當(dāng)中很多人如此。

藥物治療、健康狀況差，不好的就寢習(xí)慣（如睡覺前看電影或喝咖啡、喝酒）、晝夜生理節(jié)奏和個(gè)人本身或多或少“睡眠庫”都是讓年齡大的人抱怨失眠的主因。

百翰女子醫(yī)院的伊麗莎白 凱勒曼和牛津醫(yī)藥學(xué)校一起開始弄清真相并且做了一項(xiàng)嚴(yán)格控制的研究，他們找了18個(gè)年齡在60-76歲的實(shí)驗(yàn)對(duì)象和35個(gè)年輕的實(shí)驗(yàn)對(duì)象，年齡在18-32歲之間，所有的實(shí)驗(yàn)對(duì)象都身體健康，沒有服用過影響睡眠的藥物，甚至曾經(jīng)在過去的3個(gè)月里跨過一個(gè)時(shí)區(qū)的人都不適合參加此研究試驗(yàn)，還有那些在過去3年里夜里工作或工作連軸轉(zhuǎn)的人也不行。

在檢測(cè)到他們?cè)诩宜�眠后，這些實(shí)驗(yàn)對(duì)象被規(guī)律地引導(dǎo)去靜靜地躺下，閉上眼睛努力睡去，一個(gè)接一個(gè)連續(xù)幾天都盡可能多地達(dá)到每天睡16小時(shí)，他們擁有世界上所有的時(shí)間。

根本原因是上年紀(jì)的人只需更少的睡眠——大約少了1.5小時(shí)。

晝夜勝利節(jié)奏&喜好

一本名叫《當(dāng)前生物學(xué)》的7月24日刊在線詳細(xì)闡述了試驗(yàn)結(jié)論。科勒曼與他的合作伙伴——英格蘭薩利睡眠中心的德克 詹 迪耶克說，比起老人平均睡眠7.5小時(shí)這個(gè)數(shù)字，年輕的實(shí)驗(yàn)對(duì)象們平均每天睡9小時(shí)。

科勒曼說，年齡相關(guān)的睡眠下降包括一種均衡的區(qū)分，這種區(qū)分發(fā)生在眼球快速活動(dòng)（REM）睡眠和眼球非快速活動(dòng)（REM）睡眠之間，前者跟做夢(mèng)有關(guān)系。

科勒曼和迪耶克令實(shí)驗(yàn)對(duì)象們處于一種為晝夜生理節(jié)奏而控制的條件中，在黑夜和白晝中都允許有睡眠的時(shí)間，而且在他們睡眠來臨時(shí)監(jiān)控個(gè)人的睡眠選擇時(shí)間。

科勒曼說，而人有時(shí)在太累的情況下睡不著，卻沒有證據(jù)證明他們?cè)诓焕鄣臅r(shí)候可以睡著。

失眠和期盼

結(jié)果暗示是老年人以為他們失眠。

科勒曼在生活科學(xué)欄目告訴我們：“確實(shí)有老年人失眠，可是有些老年人如果堅(jiān)信他們需要8-9小時(shí)睡眠，因此他們會(huì)躺在床上睡覺耗費(fèi)更多時(shí)間（醒著躺在床上），這比他們需要達(dá)到的實(shí)際睡眠時(shí)間也更長(zhǎng)，這也就產(chǎn)生了他們所謂的“失眠”。

科勒曼又補(bǔ)充道：“也有可能由于年齡的變化可以入睡或是處于睡眠狀態(tài)，而有了更多睡眠的機(jī)會(huì)，他們卻睡得少了。”需要注意的是，這個(gè)新的調(diào)查結(jié)果只用于那些健康人，他們沒有經(jīng)過藥物治療，沒有用藥或是睡眠紊亂。

研究還發(fā)現(xiàn)最健康的人，尤其是年輕人達(dá)不到他們這個(gè)年齡需要的睡眠量。

有證據(jù)證明睡眠不足與劇增的危機(jī)、誤差、認(rèn)知不足和免疫系統(tǒng)功能，和類似于糖尿病的新陳代謝病變有關(guān)。科勒曼鼓勵(lì)年輕人要睡得比他們目前的睡眠時(shí)間長(zhǎng)些。

睡眠年齡

經(jīng)過生命周期后我們的睡眠習(xí)慣顯著改變這一說法不再新穎了。

同樣的研究發(fā)現(xiàn)另一個(gè)年齡影響：同樣的睡眠時(shí)間，老人往往要花費(fèi)更多的時(shí)間才能睡著。

研究人員將60歲設(shè)為一個(gè)老年實(shí)驗(yàn)對(duì)象的年齡起點(diǎn)，以此保證與年輕實(shí)驗(yàn)對(duì)象有顯著的特征，但是科勒曼說也有可能下降的睡眠量也會(huì)達(dá)到中年的歲數(shù)。

她說：“我希望這種變化是循序漸進(jìn)的，而且沒有時(shí)間指出我們處于哪個(gè)年齡段，睡眠的變化從嬰幼兒期開始，經(jīng)過兒童期、青春期、青年期和中年期知道我們死亡。”

不必要的藥物治療？

科勒曼說，這些發(fā)現(xiàn)也有可能影響老年人對(duì)失眠的治療，還有就是產(chǎn)生神奇的效果，如鍛煉、新的藥物配方，或是眼睛光線的治療。

她還說：“如果老年人相信比起他們用更多的時(shí)間用于睡覺可以達(dá)到睡眠時(shí)間，他們需要更多的睡眠，那么他們可能會(huì)抱怨自己失眠：想睡覺卻睡不著。他們可能開始使用沒必要的藥物治療。”

盡管如此，一天下來老年人也很累，他們里應(yīng)該考慮睡眠紊亂的原因，這個(gè)可能就是妨礙他們?cè)谝雇砟苡袀�(gè)好眠的原因。

此項(xiàng)研究有國(guó)家健康協(xié)會(huì)提供資金資助，迪耶克由英國(guó)生物技術(shù)和生物科學(xué)研究委員會(huì)以及威爾卡姆信托基金資助。