A Scientific Approach to Improving Sleep Quality
This is about a 2-minute read.
What Is Sleep Quality?
Sleep quality is not simply about sleeping longer. In sleep science, indicators of sleep quality include time to fall asleep, number of nighttime awakenings, proportion of deep sleep (non-REM sleep stage 3), and feeling of refreshment upon waking.
Japan's Ministry of Health, Labour and Welfare recommends at least six hours of sleep for adults in its 2023 Sleep Guidelines. However, even with the same seven hours of sleep, there is a significant difference in next-day cognitive function and mood between high-quality and low-quality sleep.
Creating an Environment for Better Sleep
Bedroom Temperature and Humidity
For example, the optimal room temperature for sleep is considered to be 16-20 degrees Celsius. The human body needs its core temperature to drop when falling asleep, and a room that is too warm prevents this temperature decrease, making it difficult to fall asleep. Humidity of 40-60% is considered comfortable.
Managing Light Exposure
Melatonin (the sleep hormone) production is suppressed by light. It is recommended to switch to warm-toned indirect lighting one to two hours before bedtime and avoid blue light from smartphones and computers.
Conversely, exposing yourself to sunlight immediately after waking resets your circadian clock and promotes melatonin production at night. Even on cloudy days, outdoor light is several times brighter than indoor lighting, so the effect is sufficient.
Sound Environment
While sudden noise disrupts sleep, research shows that consistent white noise or nature sounds can actually aid falling asleep. Using earplugs is also an effective option.
Reviewing Lifestyle Habits
Caffeine Intake Timing
For instance, caffeine has a half-life of approximately five to six hours. If you drink coffee at 2 PM, half the caffeine remains in your body at 8 PM. To minimize the impact on sleep, it is advisable to avoid caffeine after early afternoon.
The Effects of Alcohol
Alcohol speeds up falling asleep but reduces REM sleep in the latter half of the night and increases nighttime awakenings. "Nightcaps" reliably decrease sleep quality, so it is recommended to finish drinking at least three hours before bedtime.
Bathing Timing
Bathing one to two hours before bed temporarily raises body temperature, and the subsequent temperature drop promotes sleep onset. Soaking in lukewarm water (38-40 degrees Celsius) for 15-20 minutes is effective. Water that is too hot stimulates the sympathetic nervous system and has the opposite effect.
Habits That Disrupt Sleep
Smartphone Use Before Bed
Beyond the blue light issue, browsing social media and news keeps the brain in an alert state. Make it a habit to place your smartphone outside the bedroom 30 minutes before sleep.
Irregular Sleep Schedules
"Social jet lag," where wake times differ by more than two hours between weekdays and weekends, disrupts the circadian clock and leads to chronic decline in sleep quality. Ideally, wake up at the same time on weekends as on weekdays.
Reading books on sleep science can help you understand your sleep patterns more deeply.
When Improvements Don't Help
If sleep quality doesn't improve despite lifestyle changes, underlying sleep disorders such as sleep apnea syndrome or restless legs syndrome may be present. If insomnia persists for more than two weeks, consider visiting a sleep clinic. (Related books may also help)
Self-medicating with over-the-counter sleep supplements or sleeping pills is not recommended. Sleeping pills in particular carry a risk of dependency and should only be used under medical supervision.
Key Takeaways
- Creating an Environment for Better Sleep
- Reviewing Lifestyle Habits
- Habits That Disrupt Sleep
- Bedroom Temperature and Humidity
Summary - Sleep Is an Investment
Improving sleep quality positively impacts daytime performance, mental health, and long-term physical health. Using sleep-related goods can also help improve your sleep environment. Start by reducing smartphone use before bedtime.