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Did you sleep well last night? In Article 1, we discussed alarm settings for a refreshing wake-up. In Articles 2 and 3, I would like to talk about actions that promote alertness after waking up.
First thing when you wake up: Open the curtains and soak up the sun
What is your morning routine after you wake up? Some people may stay in bed a little longer after waking up, but there's something I'd like you to do before that.
That is, as soon as you wake up, open the curtains in your bedroom and bask in the sunlight. Doing so promotes alertness after waking up.
However, if you wake up much earlier than your scheduled wake-up time (e.g., during mid-sleep awakenings), exposing yourself to strong sunlight can stimulate the sympathetic nervous system, making it difficult to fall back asleep, or shifting your rhythm forward, disrupting your normal sleep rhythm. Therefore, please avoid basking in the sunlight. Also, elderly people who suffer from waking up early in the morning should avoid basking in the sun immediately after waking up.
Opening the curtains and basking in the sunlight in the morning is effective not only on sunny days but also on cloudy and rainy days.
Why bask in the sun?
Basking in the morning sun has tremendous effects. Even without looking directly at the sun, simply being exposed to sunlight activates the function of suppressing the secretion of "melatonin," a hormone secreted by the pineal gland.
Melatonin is also known as the "sleep hormone." In other words, by being exposed to sunlight, the secretion of the sleep hormone is suppressed, and sleep drive (the desire to sleep) is reduced.
Sleep-wake regulation by the third eye
The human retina contains three types of photoreceptor cells. The first are rod cells, which sense light intensity; the second are cone cells, which sense color; and the third are melanopsin-expressing retinal ganglion cells.
When light of a specific wavelength (blue light) of 470nm reaches the melanopsin-expressing retinal ganglion cells (photoreceptor proteins that are G protein-coupled receptors) (*1), which constitute a few percent of these retinal ganglion cells, a signal to suppress melatonin secretion is transmitted to and controlled by the pineal gland in the brain.
Incidentally, sunlight has a wide range of wavelengths, approximately 300nm to 3000nm (with approximately 380nm to 780nm often considered visible light), so it includes the specific wavelengths that react to melanopsin. This remains true even on rainy days.
Circadian rhythm reset effect
Melatonin secretion is said to increase approximately 14-15 hours after exposure to sunlight. Therefore, when you wake up in the morning and are exposed to sunlight, the secretion of sleep hormones increases at night, naturally making you feel sleepy.
Another important function of melatonin is the regulation (adjustment) of the circadian rhythm's phase to the light-dark cycle. The human circadian rhythm is "24.2 hours," shifting by 12 minutes each day. Melatonin plays a role in adjusting this shift. To maintain a 24-hour rhythm, it is necessary to reset the body's internal clock by signaling morning to the body each day.
Disadvantages of disrupting your circadian rhythm
Some people's rhythms are inevitably disrupted due to their occupation. Examples include medical professionals with night shifts, drivers, restaurant workers, hotel front desk staff, and security personnel.
In the case of night work, being awake at night and sleeping during the day can have undeniable negative effects on hormone balance and mental state. In fact, many people reportedly suffer from sleep disorders, dizziness, digestive problems, daytime sleepiness, and fatigue while on duty.
Furthermore, totally blind people, unable to perceive light, are constantly in a free-running state (living only by their inherent biological clock, unaffected by the Earth's rhythm), causing their internal day to gradually recede, leading to a reversed day-night internal rhythm.
As a prescription, there are melatonin supplements. In the past, they were extracted and purified from the pineal gland of pigs, but now synthetic agents are produced. Because of their easy availability, the market in the United States is approximately 200 billion yen.
However, since the efficacy and effects of supplements vary greatly from person to person, we do not recommend indiscriminately using supplements just because your rhythm is disrupted.
It should be noted that the efficacy is primarily high in the elderly. This is because as people age, melatonin secretion decreases and light perception in the retina weakens, making them prone to rhythm disturbances, and their lower secretion levels make them more sensitive to it.
Symptomatic treatment for night shift workers
It is said that variations in bedtime and wake-up times over consolidated periods, such as weekly, cause less burden than daily variations. While there may be operational constraints, if possible, it is recommended to standardize activity patterns over consolidated periods.
Also, since the internal clock can only synchronize to a new cycle by one hour per day, gradually shifting activity times is more advisable and easier for the body to adapt to than large daily fluctuations in activity times.
For example, nurses who work day, semi-night, and night shifts should gradually change their activity times, such as day shift → semi-night shift → night shift. When shifting schedules, it has been found that shifting later is easier for the body to adapt to and less stressful than shifting earlier.
Other articles introduce useful information for improving sleep quality, such as temperature control and pre-sleep behavior, so please take a look.
Social initiatives are urgently needed, not just individual ones.
It has been reported that people who work night shifts are prone to poor health, and if chronic, to lifestyle diseases such as cancer and diabetes, and mental illnesses. Companies, organizations, and society must take this fact seriously and promote environmental improvements, care, and the dissemination of knowledge.
Specifically, this includes introducing nap rooms, eliminating unreasonable shift schedules, implementing systems to prevent operational errors, subsidizing medical care such as sleep clinics, and holding in-house seminars.
Ways to maximize light changes
Keep your bedroom dark during sleep to minimize stimulation to photoreceptor cells. To maximize stimulation to photoreceptor cells when you wake up and expose yourself to sunlight, keep your bedroom dark. If possible, it's a good idea to use blackout curtains.
Since sunlight or external light entering through gaps in the curtains can cause you to wake up, there are ways to prevent this, such as securing the ends of the curtains to the window frame or placing cushions at the bottom to eliminate gaps (*2).
【References】
*1: Identification of inhibitors against the photoreceptor melanopsin and analysis of their effects on non-visual photic responses
*2: Mom and Baby's Good Sleep Book: A Guide to Resolving Night Crying, Bedtime Struggles, and Early Morning Waking
