Sleep Disorders Expert Discusses How Sleep is Influenced by the Body Clock that You are Born With | FRIDAY DIGITAL

Sleep Disorders Expert Discusses How Sleep is Influenced by the Body Clock that You are Born With

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Even if you try your best, you can’t wake up early.

Many people are said to be first-class businessmen who wake up early, and many of them engage in morning activities such as coming to work early in the morning and exercising before work. Many people believe that “morning activities = a person who can work well,” but those who are weak in the morning may find it hard.

“In fact, early morning activities do not suit everyone. Sleep studies have shown that the timing of activity, such as whether to be active in the morning or at night, differs slightly for each individual.”

Shingo Kitamura of the Sleep and Wakefulness Disorders Research Department, National Institute of Mental Health, National Center of Neurology and Psychiatry, says that “Chronological timing of activity tends to be different for each individual”. The tendency of an individual to have a timing of activity is called “chronotype”


“Morning people are good at going to bed early and waking up early, have a good appetite in the morning, and in return cannot stay awake until late at night. The opposite is true for night-types, who are not good at getting up early in the morning, feel energized in the afternoon, and go to sleep late.”

If you can’t get up early despite your best efforts, or if you are too sleepy to go out for a late night drink, it may not be a matter of your own energy, but rather the time of day that doesn’t suit your chronotype, which represents morning and night types.

”Chronotypes have been studied around the world since the late 19th century. For example, there are reports that it was used to investigate the best time for learning and to check the aptitude of military personnel,” says Kitamura (PHOTO: AFRO).

“Our bodies are equipped with an internal clock. We wake up in the morning and naturally become sleepy at night because our body clock is working regularly. Chronotype is influenced by this biological clock.”

“Chronotypes, which vary from person to person, are not divided into two types, morning and night, but rather are distributed in a smooth normal distribution, such as extreme morning type, slight morning type, intermediate type, slight night type, and extreme night type,” he says.


“This is reported to be related to the multiple genes we are born with. The extent to which genetic factors are involved in morning and evening types has been investigated in twin studies, and it is said that about half is determined by genetic factors and the other half by a variety of other factors.”

“These include, for example, age: between the ages of 10 and 20, people become increasingly nocturnal, and after the age of 20, they slowly become morning-oriented. This is why we become earlier in the morning as we age. It is also related to the amount of exposure to artificial light such as sunlight and fluorescent lamps. In other words, about half of our bodies, excluding age and environmental factors, are determined at birth by genetic factors.”

If a night person is forced to adjust to a morning schedule, his/her sleep condition will worsen.

It is natural for working people to adapt when they need to go to work early in the morning. However, if a person is an extreme night owl or tends to be a night owl, forcing him or herself to adjust to this lifestyle can have a detrimental effect on sleep.

“Extreme night-types are not sleepy even if they try their best to get into bed early,” he says. “They have to go to bed late and get up early, so they force themselves to get up after a short night’s sleep. If this continues, “sleep debt” accumulates like a debt.”

“To solve the chronic lack of sleep, people sleep until almost noon on their days off, but they miss the important morning light to reset their body clocks, so they tend to be more night-oriented. As a result, they are unable to get to sleep on the night before work, and they start Monday without enough sleep, which is a vicious cycle.”

On the contrary, extreme morning people wake up when morning comes, even if they want to sleep in slowly. Even if a morning person works overtime and goes to bed late at night, he or she will wake up early in the morning. In this case, too, sleep deprivation occurs and performance during the day declines.


“To some extent, it is genetically determined, so it is not easy for a person with an extreme morning type, an extreme night type, or a chronotype close to that to change to a lifestyle that is the exact opposite. However, those with an ‘in-between’ chronotype can change their lifestyle flexibly, depending on their efforts.”

Distribution of chronotypes based on 99414 respondents to the Munich Chronotype Questionnaire. It is clear that there are individual differences in when it is easier to sleep, wake up, and be active (Graph: Courtesy of the Sleep and Wakefulness Disorders Research Department, National Institute of Mental Health, National Center of Neurology and Psychiatry).

The Munich Chronotype Questionnaire (MCTQ) is a method of knowing one’s chronotype. It is a tool to assess chronotype and the characteristics of an individual’s biological clock.

Click here for ■ (Munich Chronotype Questionnaire Japanese version )

“The MCTQ website offers a self-assessment tool that allows you to determine your chronotype (morning or evening type) by answering questions on the MCTQ website. The results will also show you your natural bedtime and wake-up time, the degree of sleep deprivation, and the discrepancy between weekday and holiday sleep, which you can use to improve your sleep habits.”

Drinking alcohol, stimulants, and strong light can interfere with sleep.

People who have problems with sleep, such as “I don’t feel tired even after sleeping” or “I feel sluggish and sleepy during the day,” may solve their problems by adopting a natural sleep/wake routine that fits their chronotype. Besides that, Kitamura points out that there are other little problems hidden in the lives of modern people when it comes to sleep.

“Drinking alcohol at night has been shown to disturb sleep and reduce sleep quality. People who say that drinking in bed has become a habit should be careful. Simply quitting drinking alcohol will help you sleep better. Stimulants such as caffeine and cigarettes are also NG habits that make the sympathetic nervous system dominant and increase arousal.”

“Strong light such as fluorescent lamps, smartphones, and TVs that we are exposed to at night also interfere with the secretion of melatonin, which is a sleep hormone. In addition, too hot or too cold temperature and humidity in the bedroom can also affect sleep. It is recommended to use warm bedding with a slightly cooler room temperature.”


The amount of sleep Japanese people get is said to be among the lowest in the industrialized world. It is important to ensure not only quality but also sufficient quantity of sleep.

On average, the body clock is longer than 24 hours, and whether you are a morning person or a night person, your body clock will gradually shift backwards. Morning light resets this shift in the body’s clock. Even if you are a night owl, it is important to get into the habit of getting light in the morning if possible.

“The amount of sleep needed varies from person to person, but between seven and nine hours is ideal. People often say they are fine with 5 or 6 hours of sleep, but most people don’t get enough. If you find yourself sleeping longer on weekends than you do on weekdays, or if you find yourself unable to tolerate sleepiness during the daytime hours, consider it an SOS from your body.”

It has been shown that lack of sleep increases the rate of diseases such as diabetes, depression, and dementia, as well as the mortality rate.

“Those of you who are in the prime of your working lives still have a lot of energy, so a little sleep deprivation may not make you sick,” he said. “But symptoms such as fatigue and poor concentration are signs of a sleep problem. If you continue to age with your current sleep habits, there is a good chance that they will lead to illness when you reach your senior years.”

Those who have obtained a sleep habit that suits them will be one step closer to a comfortable body. Knowing your “morning type” and “night type” and incorporating them into your daytime activities and bedtime timing will help you build a foundation for a healthy body.


Shingo Kitamura is the Director of the Sleep and Wakefulness Disorders Research Department, National Institute of Mental Health, National Center of Neurology and Psychiatry. He conducts research to clarify the regulation and function of sleep, the effects of sleep disorders on the body and mind, and their relationship to various diseases. He was involved in the creation and release of the Japanese version of the Munich Chronotype Questionnaire (MCTQ), which diagnoses chronotypes.

  • Interview and text by Yoko Nemmochi

    Born in Yamagata Prefecture in 1983, Yoko Tunemochi worked for 10 years in the editorial department of a health information magazine, editing monthly magazines and web media before becoming a freelance writer. Currently, she interviews, plans, and writes about doctors and specialists, focusing on healthcare and medical fields.

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