Sleep is not "rest" but a switch that influences the age of organs

"You should get proper sleep"

This is common health knowledge that everyone knows. However, for busy modern people, sleep is often treated as "time that can be cut." If work drags on, sleep is reduced. Watching a smartphone can delay bedtime. On holidays, people sleep longer to make up for the lack of sleep during weekdays.

However, a recently published large-scale study shows that viewing sleep merely as a time for fatigue recovery is insufficient. Sleep duration may be related to the "biological age" of organs throughout the body, including the brain, heart, lungs, liver, kidneys, digestive system, immune system, metabolism, and skin.

Moreover, the important point is not a simple "the longer you sleep, the better." The study showed a U-shaped relationship, indicating that both too little and too much sleep may not be desirable for the body.

The age of the body is not determined solely by your birthday

We usually think of age as "how many years have passed since birth," which is the so-called chronological age. A 40-year-old is 40, and a 60-year-old is 60.

However, even among 60-year-olds, some can climb stairs with ease, while others struggle with chronic fatigue or illnesses. The condition of the skin, blood vessels, brain, muscles, and heart varies from person to person. In other words, the human body does not age uniformly according to the calendar.

This is where the concept of "biological age" has gained attention in recent years. It estimates how much the body's tissues and organs have actually aged based on blood components, imaging data, gene expression, metabolites, and more.

In the current study, multiple "aging clocks" based on MRI images, plasma proteins, and metabolites were used. An aging clock is a model that estimates whether an organ is younger or older than its actual age based on body data.

What is interesting is that the study looked at the aging progress of each organ and tissue, rather than viewing the entire body as a whole. The brain may be relatively young, but the heart is aging. The liver is maintained, but the metabolic system is aging beyond its years. This study aimed to observe such "age differences within the body."

The range of "6.4 to 7.8 hours" observed from data of about 500,000 people

The research team analyzed data from the UK Biobank, a large-scale health database in the UK. The subjects were middle-aged to elderly adults, and sleep duration was self-reported. They combined this with biological aging indicators created from brain and body images, proteins in the blood, and metabolites.

As a result, the relationship between sleep duration and biological age showed a U-shaped curve, not a straight line.

In other words, people with too short sleep durations tended to have higher aging indicators. On the other hand, people with too long sleep durations also tended to have higher aging indicators. The range where aging indicators were most likely to be low varied by organ and gender, but was generally around 6.4 to 7.8 hours.

The WELT article introduces this range as 6.5 to 7.8 hours, explaining that both too short and too long sleep were associated with aging of the lungs, liver, heart, digestive system, skin, kidneys, immune system, hormonal system, and metabolic system.

What is important here is not to interpret this number as "you must sleep exactly 7 hours and 12 minutes every day." The study is based on group data, and there are individual differences. The necessary sleep varies depending on constitution, age, illness, medication, lifestyle rhythm, and sleep quality.

Still, one message is clear. Sleep is not something that can be endured if it's minimal, nor is it something that is healthier the more you have. There is likely an appropriate range for the body.

Why does too little sleep age organs?

Many people know from experience that lack of sleep is bad for the body. On days of sleep deprivation, concentration drops, appetite becomes irregular, and irritability increases. However, the effects are not limited to mood and drowsiness.

Short sleep is thought to affect fundamental systems of the body, such as inflammation, blood sugar regulation, hormone secretion, autonomic nerves, and immune responses. During sleep, damage received during the day is repaired, waste in the brain is processed, immunity is adjusted, memory is organized, and metabolism is readjusted.

If this time is chronically insufficient, the body faces the next day without fully recovering. This leads to changes such as increased blood pressure, unstable blood sugar levels, persistent inflammation, and disrupted hormones that regulate appetite.

Studies have also shown that short sleep of less than 6 hours is more likely to be associated with physical diseases such as diabetes and cardiovascular diseases. This does not mean "you will get sick immediately because you slept short," but it suggests that chronic sleep deprivation may create an aging environment throughout the body.

In modern society, short sleep is sometimes spoken of as a sign of capability. "I can work on 4 hours of sleep," "Sleeping is a waste of time," "You can pull all-nighters when you're young." However, from the perspective of organs, such a lifestyle may be accumulating invisible debt.

So why is too much sleep also a problem?

Many people may find it surprising that too much sleep was also associated with increased aging indicators.

One might think, "Since sleep is good for the body, the longer you sleep, the better." However, long sleep has a complex background.

One possibility is that rather than long sleep itself being the cause, it could be that long sleep is due to existing health issues or illnesses. Chronic inflammation, depressive symptoms, sleep apnea, medication effects, metabolic abnormalities, and early changes in neurological diseases can lead to long sleep durations because the person feels they are sleeping enough but still cannot shake off fatigue.

The current study does not definitively determine the causal relationship between long sleep and health risks. It is possible that both "aging or signs of illness cause long sleep" and "long sleep causes aging" are intertwined.

This was a point that many people reacted to on social media. On Reddit, questions were posted about what happens to people who sleep long, and whether it is simply that people in poor health sleep longer. On LinkedIn, comments emphasized the need for caution regarding causality, given that it is an observational study.

This reaction is healthy. Health information can easily take on a life of its own when numbers are straightforward. If you only take away "over 8 hours is dangerous," it can cause anxiety for those who sleep long. However, what is truly important is to "consider why so much sleep is needed if long sleep continues."

It's not about having a problem because you slept long once on a holiday. If you sleep 9 or 10 hours every day and still feel strong drowsiness, persistent fatigue during the day, snoring or apnea is pointed out, or you feel down, it's more important to review the quality of sleep and underlying health conditions than to forcibly cut sleep time.

The clarity of "7 hours of sleep" and the simultaneous spread of doubts on social media

 

This study contains several elements that make it easily spreadable on social media.

"Organs age based on sleep duration"
"Ideal is 6.4 to 7.8 hours"
"Not only lack of sleep but also oversleeping is not good"
"Data from 500,000 people"

These words resonate not only with health-conscious people but also with business people struggling with lack of sleep, young people who tend to stay up late, those raising children, and shift workers.

On Facebook and Instagram, posts with the headline "Ideal Sleep Duration" emphasize the 6.4 to 7.8-hour range. The reactions are likely to include sentiments like "Sleep is indeed important," "I thought sleeping longer was better," and "I clearly don't get enough sleep."

On LinkedIn, more professional interpretations stand out. One post introduced the use of large-scale UK Biobank data, 23 types of aging clocks, and multiple data such as MRI, proteins, and metabolites, while also noting "it is an observational study and causality is unresolved." The number of reactions is high, indicating interest in sleep in the context of health management, preventive medicine, and performance management.

On Reddit, there are more reactions from a layperson's perspective. Questions were raised about what happens to people who sleep long, whether healthier people can sleep more regularly, and whether the relationship between sleep duration and illness is reversed in terms of "cause" and "effect." There were also sarcastic comments about overly simplifying numbers.

On X, posts introducing the study content in Japanese, such as "There is a U-shaped curve relationship between sleep duration and biological aging," can be seen. For Japanese readers, the numbers "less than 6 hours," "over 8 hours," and "6.4 to 7.8 hours" are quite strong hooks.

In summary, social media reactions show that this study is being received in two directions.

One is the reaction as an opportunity to review a lifestyle that has neglected sleep. The other is the caution against numbers taking on a life of their own.

Both are important. While it is crucial to re-recognize the value of sleep, there is no need to force everyone into the same sleep duration.

We should look at "sleep quality" as well as "sleep duration"

While sleep duration is a major theme in this study, what we should be conscious of in real life is not just the time.

Even if you are in bed for 7 hours, if you wake up multiple times at night, have shallow sleep, feel tired upon waking, or experience strong drowsiness during the day, the quality of sleep may not be sufficient.

The CDC also states that healthy sleep is not just about duration, but about getting enough quality sleep. For adults, roughly 7 hours or more is recommended, and as age increases, about 7 to 8 hours is a guideline. Of course, this is a general guideline, and there are individual differences.

The basics of improving sleep quality are not particularly special.

Go to bed and wake up at the same time as much as possible every day. Keep the bedroom dark, quiet, and at a comfortable temperature. Avoid smartphones and bright lights just before bed. Limit caffeine from afternoon to evening. Avoid heavy meals or alcohol before bed. Get physical activity during the day.

Though they may seem mundane, these are effective for adjusting the internal clock. More than expensive supplements or special health methods, these basics can hold greater significance.

From "boasting about lack of sleep" to "managing recovery"

The question this study poses to us is not simply "how many hours should you sleep."

It is whether we treat sleep as leftover time in our lives or as a central habit that supports a healthy lifespan.

Many people pay attention to diet and exercise but put sleep on the back burner. However, from the perspective of the biological age of organs, sleep may affect the entire body as much as or even more than diet and exercise.

A lifestyle of working hard with short sleep may yield results in the short term. However, in the long term, it may be depleting the resilience of the heart, metabolism, immune system, and brain. Conversely, if you sleep long but still feel tired, it may be a sign that your body is alerting you to some abnormality.

The important thing is not to make sleep duration a matter of personal responsibility or grit. The background that forces people to cut sleep varies, including work, caregiving, child-rearing, night shifts, commuting, and economic conditions. That is why a design that does not underestimate sleep is needed for society as a whole.

For companies, it means not valuing long working hours. For schools, it means considering the sleep rhythms of children and young people. For families, it means not just blaming smartphone habits or staying up late before bed but creating an environment conducive to sleep.

Sleep is not a health habit that can be completed solely by individual will. It reflects the very structure of life.

How to incorporate this study into daily life

What can we do immediately in response to this study?

First, understand your average sleep duration. Instead of just feeling "I am sleeping" or "I am not getting enough," record your bedtime, wake-up time, nighttime awakenings, and daytime drowsiness for about 1 to 2 weeks. You can use a smartwatch or sleep app, but a handwritten note is sufficient.

Next, if you have been sleeping less than 6 hours, consider increasing it by 30 minutes first. There is no need to suddenly change to an ideal lifestyle. Shorten SNS time by 15 minutes before bed. Move night tasks to the morning. Advance caffeine intake time. Even small changes can make a difference.

On the other hand, if you consistently sleep significantly more than 8 hours and still cannot shake off fatigue, it is dangerous to simply think "I am sleeping too much, so I should reduce it." There may be underlying issues such as sleep apnea, depressive symptoms, chronic diseases, or medication effects. It is better to consult a medical institution if necessary.

And most importantly, do not be overly controlled by numbers.

The range of 6.4 to 7.8 hours is very intriguing. However, this is a trend seen from group data and is not a prescription that fits everyone perfectly. Some people may be fine with 7 hours, while others may need close to 8 hours. The necessary sleep varies for the elderly, during recovery from illness, during pregnancy, under strong stress, and for those engaging in intense exercise.

The guideline should be the overall state, such as the sense of recovery upon waking, daytime drowsiness, concentration, mood, and whether there is extreme sleeping in on weekends.

Sleep may be the most accessible anti-aging practice

The term "anti-aging" is often associated with expensive cosmetic treatments, supplements, and special tests. However, what this study suggests is a more accessible possibility.

Every night's sleep may be related to the aging of organs.

Of course, sleep alone cannot stop aging. Many factors are involved, including genetics, diet, exercise, stress, environment, illness, and social connections. However, sleep is a relatively adjustable factor among them and a habit that affects the entire body.