Early Birds May Be at Lower Risk of Depression Than Night Owls早起鸟比夜猫子更不容易抑郁

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

一项新的研究表明，如果你是一个习惯早起的人，那么你患重性抑郁症的风险可能会降低。

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.

关于人体生理醒睡周期的多项研究表明，早起的人患抑郁症的风险更低。但这些研究是由观察所得，因此无法证明存在因果关系。

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.

例如，早起的人可能有其他影响健康的行为或生活方式可以降低罹患抑郁症的风险——比如饮食更健康，锻炼更频繁，或很少有与抑郁症相关的慢性疼痛等健康问题。这些因素和其他许多因素都可以解释抑郁症风险降低的原因，而并非早起这一个因素。此外，抑郁症本身会导致睡眠障碍，因此抑郁症可能是成为夜猫子的一个原因，而不是反过来。

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.

然而，新的研究提供了更有说服力的证据，证明早睡早起本身可以预防抑郁症，不受其他因素影响。这项研究采用了一种名为孟德尔随机化的研究方法，有助于确定可能存在的因果关系中的起因。研究报告发表在《美国医学会杂志·精神病学卷》上。

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.

运用孟德尔随机化方法，研究人员能够基于独立于其他健康或行为特征的遗传变异来比对大量人群——本例指未来会变成夜猫子还是早起鸟——这些遗传特征是胎儿在子宫内发育期间就被随机赋予的。研究人员已经确定了340多种与昼夜睡眠节律相关的遗传变异，可以将携带“早起鸟”遗传变异的大批人与缺乏这种遗传变异的人进行比对。这本质上是大自然安排的随机实验。

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.

在这项研究中，科学家们使用了两个包含80多万成年人的遗传数据库，对昼夜节律和抑郁症风险进行了孟德尔随机化研究。数据库不仅含有基因数据，也有重度抑郁的诊断数据以及人们上床和醒来时间的信息。这些信息采集于自我报告和睡眠实验室的记录，研究人员用于追踪“睡眠中点”——监测某人睡眠倾向的一种有用的科学方法。例如，一个通常在晚上10点上床、早上6点醒来的人，“睡眠中点”是凌晨2点。

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.

研究人员发现，携带早起鸟遗传变异的人，“睡眠中点”每早一个小时，患重度抑郁的风险就降低23%。

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.

时间生物学专家蒂尔·伦内贝格博士没有参与这项研究，他说这项研究的一个缺点是，科学家们没有这些人必须几点起床工作或履行其他义务的数据。他说，即使采用孟德尔随机化法，也无法解释晚睡的人经常需要过早上班的事实，而这本身可能会导致抑郁。

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

“他们从现有数据中得出了正确结论，”他说，“但生活远比这复杂。”

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.

如果你是一个夜猫子，改变习惯会减轻抑郁或降低患抑郁症的风险吗？该研究报告的主要作者、加州大学旧金山分校的住院医生伊亚斯·达格拉斯博士的回答是，不一定。他说，这项研究针对的是大批人群，而非个人。

“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.”

“现有数据告诉我们，社会的某些发展趋势”——比如夜间使用智能手机和其他蓝光设备，这会让我们更晚入睡——“可能影响群体的抑郁程度。”他说，“这些研究结果并不是说早睡就能摆脱抑郁。要发现哪种干预措施对哪些群体有效，必须留给临床试验了。”

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.”

不过，他表示：“尽管现有数据没有告诉我们最佳就寝时间，但我认为，如果你是一个晚睡的人，尤其是还得早起的话，一种有助心理健康的稳妥干预办法是，把就寝时间提前一小时左右。”

（译者为“《英语世界》杯”翻译大赛获奖者）