“How Many Hours Do You Sleep Each Day?”

The Science of Sleep

The better you sleep, the healthier you become

For modern people living busy lives, sleep deprivation has become part of the daily routine. In particular, office workers suffering from overwork often list “recovering from fatigue” as their number one health concern.

So how does quality sleep affect our health and work?

Long Working Hours Steal Sleep

The International Labour Organization (ILO) and the European Union (EU) classify working more than 48 hours per week as “long working hours.”

In Korea, the 52-hour workweek system was introduced by law to reduce excessive hours, but many employees still rely on only 4 to 5 hours of sleep each night.

According to an International Labour Office report:

Working 55+ hours per week increases the risk of shortened sleep by 2.8 times
Increases the likelihood of difficulty falling asleep (insomnia) by 7.9 times
Doubles the risk of early awakening
Raises the risk of diseases such as heart attack, stomach disorders, and depression by at least 1.3 times
Also increases suicidal thoughts

Long working hours take away sleep and threaten our health.

How Much Sleep Is Enough?

Experts recommend 6–7 hours of sleep as the ideal duration.

Less than 4 hours of sleep:
- Male mortality risk ↑ 62%
- Female mortality risk ↑ 60%

More than 10 hours of sleep:
- Male mortality risk ↑ 73%
- Female mortality risk ↑ 92%

Problems Caused by Sleep Deprivation

Impaired glucose metabolism → precursor to diabetes
Abnormal secretion of the stress hormone cortisol
Decreased leptin → increased appetite → obesity
Lower immunity and reduced white blood cells
Excess estrogen in women → increased risk of breast cancer

Can We “Catch Up” on Sleep Over the Weekend?

A study by the University of Pennsylvania found that sleeping 8–10 hours on weekends compared to 6 hours on weekdays can:

Reduce stress hormone and inflammation levels by 50%
Lower the risk of high blood pressure by 39%

But! Research also shows that sleeping more than 10 hours in one go can actually make you feel even more tired.

Why?

Because our bodies have a natural biological clock. Sleeping in on weekends disrupts this rhythm and leads to the dreaded “Monday blues.”

Sleep cannot be “stored up.”
→ To recover from fatigue, a regular sleep schedule is essential.

Want Deeper Sleep? Get Some Sunlight During the Day!

The quality of sleep depends not only on its length but also on its depth.

Sleep stages:

Light sleep (stages 1–2): easily awakened
Deep sleep (stages 3–4): immunity and body condition at their peak

A cycle of light and deep sleep repeats every 90 minutes. But when sleep is too short or stays in light stages, it leads to insomnia and accumulated fatigue.

How to Improve Deep Sleep

Doctors often recommend this to insomnia patients:
“Take a walk for about an hour under bright sunlight during the day.”

Why?

Sunlight regulates the body’s rhythm of melatonin (the sleep-inducing hormone)
Melatonin, suppressed during the day, is released at night to help induce deep sleep

So, how well are you sleeping tonight?
For your health, it may be time to start investing in better sleep. Begin with something simple—enjoying a walk in the sunlight during the day.

Sleep is the beginning of recovery.
Working more than 55 hours a week threatens both sleep and health.
6–7 hours of regular sleep is most ideal.
Sunlight exposure during the day is the best preparation for a good night’s rest.
“Catching up” on sleep over the weekend may add fatigue rather than remove it.

Long working hours increase the risk of sleep reduction by 2.8 times—and significantly raise the risk of disease.