Pitfall of six-hour sleep


A research on sleep conducted by Stanford University has revealed that sleep debt, piled up like a loan through recurrence of slight lack of sleep, is likely to have harmful effects on mind and body even if you may think, “I’ve enough sleep.” How will sleep debt change your knowledge about sleep?

In the first place, where should we draw a line about lack of sleep? It is needless to say that extremely poor sleep, such as “studying all night for exams” or “leading a daily life with two hours of sleep”, will certainly have adverse impacts on mind and body. Then, what impression do you have when you hear about “six hours of sleep per night”? Many of you may think that with that much sleep, one does not need to worry about lack of sleep.

In reality, however, six hours of sleep is not sufficient. According to a survey on social life conducted in 2011 by the Statistics Bureau, the Ministry of Internal Affairs and Communications, Japanese people sleep for seven hours and 42 minutes on average, or much longer than six hours. The National Sleep Foundation (NSF), a U.S. nonprofit organization that promotes researches on sleep, updated in 2015 its recommended sleep hours, advising people aged 18 to 25 to sleep seven to nine hours. From both data, it is clear that six hours of sleep leaves many people short of sleep by a couple of hours per day. If this is repeated, they may end up with sleep debt.

Moreover, it is said that poor sleep of around six hours is more dangerous than extreme lack of sleep such as night-long work. When you sit up all night, you will be attacked by heavy drowsiness the day after and may feel “I must improve my lifestyle habit”. On the other hand, you may fail to realize lack of sleep if you have six hours of sleep every day. In fact, however, damage to your body steadily gets heavier irrespective of whether you feel sleepy or not. In other words, poor sleep accumulates to generate sleep debt before you realize it. So, people who think they are OK with six hours of sleep need to recognize the existence of sleep debt and rethink about their sleep hours. (Written by Yuta Uchino)



しかし、実際には6時間では睡眠不足なのだ。総務省統計局の平成23年社会生活基本調査によると、日本人の平均睡眠時間は7時間42分であり、6時間の睡眠では平均を大きく下回ることになる。また、睡眠に関する研究を行っている米国の「全米睡眠財団」(National Sleep Foundation)は2015年に新たに推奨睡眠時間のデータを改定し、18~25歳の人の推奨睡眠時間を7~9時間とした。このことからも、多くの人にとって6時間の睡眠では1~2時間程度の睡眠不足となることがわかる。そして、これを毎日積み重ねることで睡眠負債を抱えることになるのだ。



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