For the average adult, the current recommendation is somewhere between seven to nine hours of sleep a night.

目前，一般成年人的建議睡眠時間是每晚大約七至九小時。

And what we've been finding from large-scale epidemiological studies is that, using that reference point of seven to nine hours,

大規模流行病學研究發現，以七至九小時作為基礎點，

once you start to drop below that, your mortality risk actually starts to increase.

一旦低於這個睡眠時間，死亡風險將會增加。

In fact, the Center for Disease Control in the United States, or the CDC, they stipulate a minimum of seven hours of sleep a night for the average adult.

美國疾病管制中心（CDC）表明，一般成年人每晚最少需睡足七小時。

In other words, the shorter your sleep, the shorter your life.

換句話說，一個人的睡眠時間越短，壽命就越短。

But it turns out that it's not quite a linear relationship as you would expect.

但與預期不同，這兩者實際上不完全呈線性關係。

It's not as though the more and more that you sleep, the lower and lower your mortality risk is.

並不是睡眠時間越長，死亡風險就越低。

In fact, something strange happens.

事實上，結果格外神奇。

Once you get past nine hours, you actually start to see a rise back up in mortality risk, which seems rather strange and peculiar.

一旦睡眠時間超過九小時，死亡風險反而會開始上升，這看起來十分奇怪且不合常理。

And scientists have actually put forward at least two different explanations.

科學家針對這點提供了兩種以上不同的解釋。

The first is that, if you look at those studies, it may be that individuals are suffering from significant disease and illness.

首先，仔細看一下這些研究，你會發現這些研究對象可能患有嚴重疾病。

When we become infected, or we have disease, typically, we try to sleep longer, we stay in bed longer.

當人生病時，通常會傾向拉長睡眠時間，而待在床上時間也變長。

So in other words, it was the unmeasured disease and sickness in those studies that was triggering a response in those individuals to try and sleep more.

也就是說，這些研究並沒有考慮到，正是疾病和不適症狀讓受試者睡眠時間拉長。

That's one explanation.

這是其中一種解釋。

The second possible explanation is poor sleep quality because we know that sleep quality, independent of sleep quantity, is also associated with mortality risk.

第二種解釋則是睡眠品質不佳，我們知道就算不考慮睡眠時間，睡眠品質也會影響死亡風險。

And the lower that your quality of sleep is, the higher your risk of death.

睡眠品質越低，死亡風險就越高。

People who have poor quality of sleep will typically try to sleep longer.

而那些睡眠品質不佳的人通常會嘗試睡久一點。

They'll try to stay in bed longer to overcome that poor quality of sleep.

他們會待在床上更久來彌補睡眠品質不佳的問題。

It may be poor quality of sleep masquerading as long sleep that is associated with a higher risk of death, rather than the long sleep itself.

導致死亡風險升高的可能是睡眠品質低落，而不單是睡眠時間長。

But if we take a step back and think about society overall, I think modernity is constantly pushing us to, perhaps, work long hours and therefore neglect our sleep.

但退一步看看整個社會，我認為是現代社會讓我們長期處於工時長的狀態，而忽略了睡眠。

But if we want to be around long enough to get the benefits and the fruits of all of that hard labor, we may want to think about starting to prioritize our sleep some more.

但如果想活到能享受辛勤工作的成果，我們或許該開始將睡眠列為優先考量。