尼古拉斯·巴卡勒 楊綺帆

If you are a morning person， you may be at reduced risk for major depression， a new study suggests.

Several studies of the body’s circadian sleep-wake cycle have shown that being an early bird is associated with a lower risk for depression. But those studies were observational so could not prove cause and effect.

For example， people who are early birds may have other health or lifestyle behaviors that reduce their risk for depression—they may have a healthier diet， for example， exercise more， or have fewer health conditions， such as chronic pain， that are associated with depression. All these factors， and many others， could explain the decreased risk for depression， and not the fact of being an early bird. Moreover， depression itself causes sleep disturbances， so it could be that depression is a cause of being a night owl， rather than the other way around.

The new study， however， offers more compelling evidence that going to bed early and waking early may， in itself， provide protection against depression， independent of other factors. The study， published in JAMA Psychiatry， uses a research method called Mendelian randomization that helps pinpoint the cause of what may be a cause-and-effect relationship.

With Mendelian randomization， researchers can compare large groups of people based on genetic variants that are independent of other health or behavioral characteristics—in this case， the tendency to being a night owl or a morning person， inherited traits that are randomly allocated during our development in the womb. More than 340 genetic variants associated with circadian sleep rhythm have been identified， and the researchers can compare large groups of people with the genetic variants for being a morning person with groups that lack them. Nature has， in essence， set up the randomized experiment for them.

For the study， the scientists used two genetic databases of more than 800，000 adults to do a Mendelian randomization study of circadian rhythm and the risk for depression. They not only had genetic data， but also data on diagnoses of major depression and information on when people went to bed and woke up， collected with both self-reports and sleep laboratory records， which the researchers used to track the midpoint of sleep1， a helpful scientific measure of someone’s sleep tendencies. A morning person who tended to go to bed at 10 and wake up at 6， for example， would have a sleep midpoint of 2 a.m.

They found that in people with the genetic variants for being an early bird， for every hour earlier the sleep midpoint， there was a 23 percent lower risk of major depression.

Dr. Till Roenneberg， an expert in chronobiology who was not involved in the research， said a shortcoming of the study was that the scientists had no data on when these people had to rise for work or other obligations. Even with Mendelian randomization， he said， they can’t account for the fact that late types often need to go to work too early， which in itself may contribute to depression.

“They’ve drawn the right conclusions from their data，” he said， “but life is more complicated than that.”

If you are a night owl， will changing your habits alleviate depression or decrease the risk for developing it？ Not necessarily， said the lead author， Dr. Iyas Daghlas， a resident physician at the University of California， San Francisco. The study， he said， looks at large groups of people， not individuals.

“This data tells us that certain trends in society”—such as using smartphones and other blue light devices at night， which make us go to sleep later—“may be having an effect on the level of depression in the population，” he said. “These results do not say that if you go to sleep earlier， you’ll get rid of depression. Discovering which intervention in which populations will be effective—that has to be left to clinical trials.”

Still， he said， “While our data doesn’t tell us where the sweet spot2 is， I would say that if you’re an evening person， especially one who has to wake up early， advancing your bedtime about an hour or so is a safe intervention that might be helpful for your mental health.”

一項(xiàng)新的研究表明，如果你是一個(gè)習(xí)慣早起的人，那么你患重性抑郁癥的風(fēng)險(xiǎn)可能會(huì)降低。

關(guān)于人體生理醒睡周期的多項(xiàng)研究表明，早起的人患抑郁癥的風(fēng)險(xiǎn)更低。但這些研究是由觀察所得，因此無(wú)法證明存在因果關(guān)系。

例如，早起的人可能有其他影響健康的行為或生活方式可以降低罹患抑郁癥的風(fēng)險(xiǎn)——比如飲食更健康，鍛煉更頻繁，或很少有與抑郁癥相關(guān)的慢性疼痛等健康問(wèn)題。這些因素和其他許多因素都可以解釋抑郁癥風(fēng)險(xiǎn)降低的原因，而并非早起這一個(gè)因素。此外，抑郁癥本身會(huì)導(dǎo)致睡眠障礙，因此抑郁癥可能是成為夜貓子的一個(gè)原因，而不是反過(guò)來(lái)。

然而，新的研究提供了更有說(shuō)服力的證據(jù)，證明早睡早起本身可以預(yù)防抑郁癥，不受其他因素影響。這項(xiàng)研究采用了一種名為孟德?tīng)栯S機(jī)化的研究方法，有助于確定可能存在的因果關(guān)系中的起因。研究報(bào)告發(fā)表在《美國(guó)醫(yī)學(xué)會(huì)雜志·精神病學(xué)卷》上。

運(yùn)用孟德?tīng)栯S機(jī)化方法，研究人員能夠基于獨(dú)立于其他健康或行為特征的遺傳變異來(lái)比對(duì)大量人群——本例指未來(lái)會(huì)變成夜貓子還是早起鳥(niǎo)——這些遺傳特征是胎兒在子宮內(nèi)發(fā)育期間就被隨機(jī)賦予的。研究人員已經(jīng)確定了340多種與晝夜睡眠節(jié)律相關(guān)的遺傳變異，可以將攜帶“早起鳥(niǎo)”遺傳變異的大批人與缺乏這種遺傳變異的人進(jìn)行比對(duì)。這本質(zhì)上是大自然安排的隨機(jī)實(shí)驗(yàn)。

在這項(xiàng)研究中，科學(xué)家們使用了兩個(gè)包含80多萬(wàn)成年人的遺傳數(shù)據(jù)庫(kù)，對(duì)晝夜節(jié)律和抑郁癥風(fēng)險(xiǎn)進(jìn)行了孟德?tīng)栯S機(jī)化研究。數(shù)據(jù)庫(kù)不僅含有基因數(shù)據(jù)，也有重度抑郁的診斷數(shù)據(jù)以及人們上床和醒來(lái)時(shí)間的信息。這些信息采集于自我報(bào)告和睡眠實(shí)驗(yàn)室的記錄，研究人員用于追蹤“睡眠中點(diǎn)”——監(jiān)測(cè)某人睡眠傾向的一種有用的科學(xué)方法。例如，一個(gè)通常在晚上10點(diǎn)上床、早上6點(diǎn)醒來(lái)的人，“睡眠中點(diǎn)”是凌晨2點(diǎn)。

研究人員發(fā)現(xiàn)，攜帶早起鳥(niǎo)遺傳變異的人，“睡眠中點(diǎn)”每早一個(gè)小時(shí)，患重度抑郁的風(fēng)險(xiǎn)就降低23%。

時(shí)間生物學(xué)專(zhuān)家蒂爾·倫內(nèi)貝格博士沒(méi)有參與這項(xiàng)研究，他說(shuō)這項(xiàng)研究的一個(gè)缺點(diǎn)是，科學(xué)家們沒(méi)有這些人必須幾點(diǎn)起床工作或履行其他義務(wù)的數(shù)據(jù)。他說(shuō)，即使采用孟德?tīng)栯S機(jī)化法，也無(wú)法解釋晚睡的人經(jīng)常需要過(guò)早上班的事實(shí)，而這本身可能會(huì)導(dǎo)致抑郁。

“他們從現(xiàn)有數(shù)據(jù)中得出了正確結(jié)論，”他說(shuō)，“但生活遠(yuǎn)比這復(fù)雜。”

如果你是一個(gè)夜貓子，改變習(xí)慣會(huì)減輕抑郁或降低患抑郁癥的風(fēng)險(xiǎn)嗎？該研究報(bào)告的主要作者、加州大學(xué)舊金山分校的住院醫(yī)生伊亞斯·達(dá)格拉斯博士的回答是，不一定。他說(shuō)，這項(xiàng)研究針對(duì)的是大批人群，而非個(gè)人。

“現(xiàn)有數(shù)據(jù)告訴我們，社會(huì)的某些發(fā)展趨勢(shì)”——比如夜間使用智能手機(jī)和其他藍(lán)光設(shè)備，這會(huì)讓我們更晚入睡——“可能影響群體的抑郁程度。”他說(shuō)，“這些研究結(jié)果并不是說(shuō)早睡就能擺脫抑郁。要發(fā)現(xiàn)哪種干預(yù)措施對(duì)哪些群體有效，必須留給臨床試驗(yàn)了?！?/p>

不過(guò)，他表示：“盡管現(xiàn)有數(shù)據(jù)沒(méi)有告訴我們最佳就寢時(shí)間，但我認(rèn)為，如果你是一個(gè)晚睡的人，尤其是還得早起的話，一種有助心理健康的穩(wěn)妥干預(yù)辦法是，把就寢時(shí)間提前一小時(shí)左右。”

（譯者為“《英語(yǔ)世界》杯”翻譯大賽獲獎(jiǎng)?wù)撸?/p>

1 midpoint of sleep 睡眠中點(diǎn)，即睡覺(jué)時(shí)間和起床時(shí)間之間的中間點(diǎn)。

2 sweet spot 最佳點(diǎn)，最有效點(diǎn)。