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.
毕竟 人的一生中有24年在睡觉 其重要性可想而知。研究者试图检验出人每晚所需的睡眠时间，通过一段时间内 让多组实验者每天晚上睡4 6或8小时。
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小时的人，更少出现注意力分散或认知问题。而每晚睡6或4个小时的人在此方面出现显著下降。仅仅两周后 睡6小时的人所做出的反应，同血液酒精含量为0.1%的醉酒者相当。睡4小时的人在认知测试期间更常打瞌睡。
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?
两组实验者的大脑功能日渐减退，其趋势呈直线下降 没有稳定的趋势。研究者将这种累积效应称为“睡眠负债“。那么 我们能从中恢复吗？
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.
经过一两个不眠之夜后，研究发现 几天的好觉可使身体和大脑彻底恢复。而经过数周 甚至数月的长期睡眠剥夺后，认知功能的恢复会慢得多，需要更多天数的高质量睡眠，而数月数年（睡眠剥夺）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？大多数研究倾向于表明 一般人最佳睡眠时长为7-8小时。除了认知问题 经常睡不满7小时的人，患心脏病 肥胖和糖尿病的风险更高。更别提死亡风险上升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 尽管睡眠超过8小时，不会损害大脑功能。它也同样会提升患心脏病 肥胖和糖尿病的风险，并且死亡风险上升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.
不过 变化当然存在 而其他主要原因便是基因。事实上 只睡6小时而不受其影响的人，被发现有一种特定基因的变异。当科学家修改老鼠基因 使其表达这一特性后，这种老鼠可比普通老鼠多清醒1.2小时。
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.