Science for Quality Sleep

Learn about environment preparation, pre-sleep routines, and understanding sleep cycles for improving sleep quality based on scientific evidence.

Created: 2025-11-14 Updated: 2025-11-14
Sleep Health Lifestyle Wellness

Three Elements That Determine Sleep Quality

Sleep quality is determined not just by time but by "depth," "continuity," and "timing." If you have the experience of not feeling rested even after 7 hours of sleep, there may be a problem with one of these elements.

According to sleep research, the ideal sleep time for adults is 7-9 hours, but there's individual variation, and finding the sleep time that suits you is important.

Understanding Sleep Cycles

Human sleep consists of approximately 90-minute cycles.

  • REM sleep: Brain is actively working, memory organization and learning content consolidation occur
  • Non-REM sleep (light): Appears immediately after falling asleep and gradually transitions to deep sleep
  • Non-REM sleep (deep): Body recovery and growth hormone secretion are most active

Going through 4-6 cycles per night completes body and mind recovery. Waking in the middle of a sleep cycle tends to leave fatigue even if you slept for a long time.

Optimizing Sleep Environment

Temperature and Humidity

The ideal bedroom temperature is 16-20 degrees Celsius, humidity is 40-60%. Since drowsiness is induced when body temperature drops, keeping the bedroom slightly cool is effective.

Light Environment

Melatonin (sleep hormone) secretion is suppressed by light.

  • Set lighting dim 2 hours before bed
  • Reduce use of devices emitting blue light
  • Block outside light with blackout curtains

Sound Environment

Sudden sounds disturb sleep. Using earplugs or white noise machines is one option.

Building Pre-Sleep Routines

To send a signal to your body that "we're going to sleep now," doing the same routine every day is effective.

  1. Bathing: Raise body temperature by bathing 90 minutes before bed, then induce drowsiness as temperature drops
  2. Light stretching: Release muscle tension and guide to relaxed state
  3. Reading: Choose paper books over e-books
  4. Breathing techniques: 4-7-8 breathing method (inhale 4 seconds, hold 7 seconds, exhale 8 seconds)

Habits to Avoid

  • Caffeine intake (until 6 hours before bed)
  • Excessive alcohol consumption (degrades sleep quality)
  • Intense exercise (until 3 hours before bed)
  • Heavy meals (until 2 hours before bed)

Adjusting Circadian Rhythm

By aligning your body clock, you can get natural drowsiness and wakefulness.

  • Fix wake time: Wake at the same time on weekends as weekdays
  • Morning light exposure: Expose yourself to natural light for 15-30 minutes within 30 minutes of waking
  • Keep naps short: Within 15-20 minutes, finish by 3 PM

How to Check Sleep Quality

You can evaluate your sleep quality with the following items:

  • Can fall asleep within 15-20 minutes of getting into bed
  • Rarely wake during the night
  • Can wake without an alarm clock
  • Don't feel strong drowsiness during the day
  • No fatigue upon waking

If 3 or more don't apply, there's room for improvement in sleep quality.

Summary

Quality sleep consists of three pillars: environment preparation, pre-sleep routine, and circadian rhythm management. You don't need to change everything at once. Start by fixing wake time first, and gradually incorporate other elements for sustainable sleep improvement. Sleep is the foundation of physical and mental health and an important element directly connected to daytime performance.

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