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Many people probably compensate for not getting enough sleep on busy weekdays by sleeping in on weekends. However, you might also hear the phrase, "sleeping in doesn't work." This article introduces information about the effectiveness of sleeping in and how to make it more effective.
Does sleeping in work?
"Sleeping in" refers to getting a lot of sleep on holidays. Although it's a commonly used term, it's actually not about "storing" sleep but rather compensating for sleep deprivation during the weekdays.
The effectiveness of sleeping in is a debated topic. Let's look at the reasons on both sides.
Reasons why it's said to be effective
Previously, it was believed that sleeping in couldn't make up for daily sleep deprivation, but now, there's a view that sleeping in on weekends can be effective.
For example, according to a paper published by a research team at Stockholm University in 2018, even if you sleep for 5 hours on weekdays, supplementing with 9 hours of sleep on weekends to make up for sleep deprivation does not increase the risk of mortality.
Also, when you are extremely tired and have accumulated fatigue factors in your brain, it is believed that prolonged sleep allows restorative factors to catch up with the repair process.
Reasons why it's said to be ineffective
While sleeping in is said to have some effect, there are also experts who believe it is not effective.
For example, Dr. Alex Dimitriu, a psychiatrist and sleep medicine specialist, believes that while some sleep deprivation can be recovered by sleeping in, it takes a very long time to recover from a large accumulation of sleep deprivation, and it becomes difficult to fully recover if the accumulation is too great.
Furthermore, Dr. James A. Rowley, former president of the American Academy of Sleep Medicine Foundation, believes that to make up for one hour of sleep deprivation, one extra hour of sleep is not enough, and four consecutive days of 7-9 hours of quality sleep are needed.
For example, if a person who needs 7 hours of sleep a day consistently sleeps 6 hours on weekdays, they will have accumulated 5 hours of sleep debt by the weekend. To recover, they would need 20 consecutive days of 7-9 hours of quality sleep. Therefore, even if they add 1-2 hours of sleep on the weekend, it won't make up for a week's worth of sleep deprivation.
Moreover, according to the Ministry of Health, Labour and Welfare's "Guidelines for Sleep for Health Promotion 2014," it states, "If sleep deprivation continues for a long time, it becomes difficult to recover from fatigue. To prevent the accumulation of fatigue due to sleep deprivation, it is important to secure the necessary amount of sleep every day."
It is important to get the necessary amount of sleep every day, and sleeping a lot on weekends does not mean you can endure subsequent sleep deprivation. It also states, "If sleep deprivation accumulates, even if you try to get a lot of sleep on holidays, you cannot adequately compensate for the decrease in efficiency due to sleep deprivation."
Sleep Debt and Catching Up on Sleep
"Sleep debt" is a concept that Professor William C. Dement, the first director of the Stanford University Sleep and Circadian Neurobiology Laboratory, the world's leading sleep research institute, began using in the 1990s. It means that "humans need a certain amount of sleep, and if they sleep less than that, the deficit accumulates. In other words, a sleep debt is incurred."
While the general term used is "sleep deprivation," sleep researchers refer to a state of insufficient sleep as "sleep debt." When a lack of sleep becomes chronic, it leads to sleep debt, which has a significant impact on both the brain and body.
Accumulated sleep debt reduces brain performance
There is a close relationship between sleep deprivation and daytime performance, to the extent that "two weeks of 6 hours of sleep per night is equivalent to the brain performance after an all-nighter."
Even if you sleep in, you cannot "store" sleep; you are merely compensating for a deficit. Furthermore, it is difficult to make up for excessive sleep debt simply by sleeping in a lot. Therefore, it is most important not to accumulate sleep debt in the first place.
Things to be careful about when sleeping in
While sleeping in doesn't fully make up for sleep debt, it's generally considered better to sleep in on weekends if that's the only time you can get adequate sleep, rather than doing nothing. When doing so, it's important to be mindful of "social jetlag."
What is "social jetlag"?
"Social jetlag" refers to the shift in sleep and wake rhythms caused by the difference between weekdays with social constraints such as work, school, and housework, and weekends without such constraints. This shift in internal rhythm can lead to difficulty falling asleep at night and decreased sleep quality the following week, so be careful.
It's fine to wake up a little later to recover from fatigue accumulated during the week, but waking up many hours later than usual is not good, as a significant shift in the timing of morning light exposure can disrupt your internal rhythm. It's said that your body clock can easily go awry if your wake-up time shifts by 2 hours, so when you sleep in, try to keep it within 2 hours.
When you want to sleep in, it's important to go to bed earlier than usual and maintain the same wake-up times on weekdays and weekends. Doing so can prevent the worsening of your sleep rhythm that can accompany sleeping in.
Better alternatives to sleeping in
According to the Ministry of Internal Affairs and Communications' "2011 Survey on Time Use and Leisure Activities," the average sleep duration for all ages in Japan is 7 hours and 49 minutes for men and 7 hours and 36 minutes for women. Furthermore, for the busy working and child-rearing generation aged 35-39, this shortens to 7 hours and 24 minutes for men and 7 hours and 22 minutes for women. The shortest sleep duration for both men and women is in the 45-49 age group, with men averaging 7 hours and 18 minutes and women 6 hours and 48 minutes.
Furthermore, when sleep duration is viewed by day of the week, within a 24-hour period (starting from 0:00 AM), weekdays average 7 hours and 31 minutes, Saturdays 8 hours and 2 minutes, and Sundays 8 hours and 16 minutes, with Sundays being 45 minutes longer than weekdays.
As stated, "Looking at the trend in sleep duration over the past 25 years for people aged 15 and over, for whom comparable age groups exist, both men and women show a decreasing trend, with a decrease of 10 minutes for men and 6 minutes for women compared to 1986." It is difficult for busy modern people to secure long sleep hours every day.
Therefore, recently, attention has been focused more on sleep quality than on sleep duration.
"REM sleep" and "non-REM sleep"
There are two types of sleep: "non-REM sleep" (a state where both the brain and body are in deep sleep) and "REM sleep" (a state where the body is resting but the brain is awake).
Although there are individual differences, generally, immediately after falling asleep, the state is deep non-REM sleep, which then changes to shallow REM sleep approximately 90 minutes after falling asleep. This cycle of non-REM and REM sleep repeats 4-5 times a night in approximately 90-minute intervals. As morning approaches, the non-REM sleep intervals shorten, and the REM sleep intervals lengthen.
The first 90 minutes of sleep are crucial.
Among these, the first 90 minutes are particularly important. The first 90 minutes after falling asleep are so crucial that it's said, "If the quality of the first 90 minutes of sleep is poor, the quality of sleep will remain poor no matter how many hours you sleep afterward." This is because the deeper the sleep during these golden 90 minutes, the more "sleep pressure" (the desire to sleep) is released, and the balance of the autonomic nervous system and hormones is regulated.
During the initial golden 90 minutes, five crucial physiological phenomena of sleep are particularly active: "brain and body rest," "memory organization and consolidation," "hormone balance adjustment," "immune system boost," and "removal of brain waste products."
Growth hormone, which is said to play important roles such as creating necessary elements for the body like skin, bones, and muscles, as well as promoting cell proliferation, normal metabolism, and anti-aging, is secreted in greater amounts by deeply sleeping during the "golden 90 minutes." This also improves the quality of subsequent sleep, thereby regulating the overall sleep cycle.
While much remains unclear about the relationship between the brain and sleep, it is known that patients with depression and schizophrenia often experience the onset of REM sleep quickly without sufficient initial non-REM sleep. From this, it is thought that the quality of the initial non-REM sleep may be extremely important.
To avoid relying on sleeping in
If you've accumulated too much sleep debt, sleeping in won't be very effective. However, if you're careful to maintain your wake-up time while sleeping in, you can make up for some sleep debt without disrupting your sleep rhythm.
For those who can't get long hours of sleep every day, why not focus on sleep quality so you can feel good without having to sleep in?
[References]
※ Ministry of Health, Labour and Welfare: Guidelines for Sleep for Health Promotion 2014
※ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7003477/
※ Ministry of Internal Affairs and Communications: "2011 Survey on Time Use and Leisure Activities"
