Tired? We all know the feeling .Irritable, groggy and exceptionally lazy. Chances are, you didn't sleep enough last night, or the past few nights.
But, what exactly is enough sleep? And more importantly, can you ever catch up on it? Well, the very function of sleep is still debated by scientists; we do know that it is necessary to function efficiently and productively.
After all, we spend 24 years of our lifetime sleeping, it'd better be important. Researchers have tested how much is required each night by assigning groups of people to 4, 6 and 8 hours of sleep over extended periods of time.
畢竟 人的一生中有24年在睡覺 其重要性可想而知。研究者試圖檢驗出人每晚所需的睡眠時間，通過一段時間內 讓多組實驗者每天晚上睡4 6或8小時。
After 14 days, those with 8 hours of sleep exhibited fewer attention lapses or cognitive issues. However, those with 6 or 4 hours of sleep showed a steady decline .In fact, after only 2 weeks, the 6 hours group showed a similar reaction time to a person with the blood alcohol concentration of 0.11% which is considered legally drunk, The 4 hours sleeper suffered even more occasionally falling asleep during their cognitive tests.
14天后 每晚睡8小時的人，更少出現注意力分散或認知問題。而每晚睡6或4個小時的人在此方面出現顯著下降。僅僅兩周后 睡6小時的人所做出的反應，同血液酒精含量為0.1%的醉酒者相當。睡4小時的人在認知測試期間更常打瞌睡。
In both groups, brain functions decrease day by day, almost linearly, with no sign of leveling off. Scientists have dubbed this cumulative effect as "sleep Dept". So, can we recover from it?
兩組實驗者的大腦功能日漸減退，其趨勢呈直線下降 沒有穩定的趨勢。研究者將這種累積效應稱為“睡眠負債“。那么 我們能從中恢復嗎？
After a night or two of little sleep, study show that the body and brain can fully recover with a few nights of good sleep. However, with long-term sleep deprivation on the scale of weeks to months, the recovery of cognitive function is much slower, requiring many more nights of quality sleep. On the time scale of months to years.
經過一兩個不眠之夜后，研究發現 幾天的好覺可使身體和大腦徹底恢復。而經過數周 甚至數月的長期睡眠剝奪后，認知功能的恢復會慢得多，需要更多天數的高質量睡眠，而數月數年（睡眠剝奪）之后.
It's unknown whether brain function could be fully repaired, or if it causes permanent damage. Paradoxically, with chronic sleep deprivation, your sleepiness or how tired you feel does eventually level off, meaning that you become less and less aware of your objective impairment over time.
So, how long should you sleep? Most studies tend to show that 7-8 hours of sleep is average ideal for humans. Apart from the cognitive issues, individuals who consistantly sleep less than 7 hrs a night have an increased risk of heart disease, obesity and diabetes. Not to mention a 12% higher risk of death.
那么 睡多久才好呢？大多數研究傾向于表明 一般人最佳睡眠時長為7-8小時。除了認知問題 經常睡不滿7小時的人，患心臟病 肥胖和糖尿病的風險更高。更別提死亡風險上升12%。
On the flip side, studies have shown that while sleeping more than 8 hours does not impair brain function; it also carries an increased risk heart disease, obesity and diabetes, and a 30% increase risk of mortality. So, too much sleep may also be a bad thing.
而另一方面 研究也表明 盡管睡眠超過8小時，不會損害大腦功能。它也同樣會提升患心臟病 肥胖和糖尿病的風險，并且死亡風險上升30%。那么,睡的太多也不好。
But variation most certainly exists, and our genetics play a large role. In fact, individuals genuinely unaffected by only 6 hours of sleep were found to have a mutation of a specific gene. When scientists genetically engineered mice to express this gene, they were able to stay awake for an extra of 1.2 hours than normal mice.
不過 變化當然存在 而其他主要原因便是基因。事實上 只睡6小時而不受其影響的人，被發現有一種特定基因的變異。當科學家修改老鼠基因 使其表達這一特性后，這種老鼠可比普通老鼠多清醒1.2小時。
It turns out, these short sleepers have more biologically intense sleep sessions than the average person.
Ultimately, while it's important to know the ideal average of 7-8 hours exist. Let your body and brain help you figure out its own needs. After all, no one's shoe size fits all.