Vol. 12: Thinking 'I'm fine' with 6 hours of sleep is a dangerous misconception.

"I'm fine with just 6 hours of sleep" or "It's a virtue to sacrifice sleep for work"—these values are still deeply rooted in Japan, but as a sleep specialist, I must be clear.

Short sleep duration is a matter of life and death.

The Ministry of Health, Labour and Welfare's "Sleep Guide for Health Promotion 2023" recommends that adults ensure at least 6 hours of sleep. The reason for the "6-hour" benchmark is that falling below this threshold statistically and significantly increases the risk of hypertension, diabetes, heart disease, depression, and dementia.
It has also been shown that the risk of stroke and heart disease increases, and as a result, short sleep duration has been shown to shorten life expectancy.

Some might say, "Isn't 7 to 8 hours ideal?" And they are right. However, I believe that setting "defending 6 hours" as the initial goal is the most realistic approach.

The scary thing about sleep deprivation is that it is difficult to notice the symptoms.

A study by Van Dongen et al. at the University of Pennsylvania (Sleep, 2003) showed that cognitive function after two weeks of 6 hours of sleep per night drops to a level equivalent to two days of total sleep deprivation (two consecutive all-nighters). Despite this, the individuals themselves feel that they are "doing fine." This is because the brain recognizes that level of performance as "normal."

"If I cut back on sleep, I'll have more time"—this may seem true at first glance, but considering the decline in concentration and productivity, it is actually counterproductive. Working for 2 hours after 8 hours of sleep results in higher quality output than working for 4 hours after 6 hours of sleep.

As a sleep specialist, I have seen many patients in my clinic who insist that they are "fine with short sleep" while their objective functioning is significantly impaired. Sleep problems are the hardest for the individual to notice. This is because the decline in performance is perceived as "normal." The lack of subjective symptoms is, in itself, a sign of danger.

Reference:
Ministry of Health, Labour and Welfare "Sleep Guide for Health Promotion 2023"https://www.mhlw.go.jp/content/001156464.pdf
Van Dongen HP, et al. "The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation." Sleep. 2003;26(2):117-26. PMID: 12683469.

*The content of this note represents the author's personal views. It has no relation to the views of the medical institution the author is affiliated with. While every effort has been made to ensure the accuracy of the content, I would appreciate it if you could point out any inappropriate content should you find any.

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