Is it possible to create living spaces that correct disruptions to our internal clocks, and reduce the risk of “social jetlag”? To explore ways of better matching living spaces with our internal clocks, we interviewed Masashi Yanagisawa, a specialist in sleep medicine and director of the University of Tsukuba’s International Institute for Integrative Sleep Medicine (WPI-IIIS). Correct understanding of our internal clock should provide hints for future living spaces that improve our quality of life.
“We spend some one-third of our life asleep, but the functions of sleep and biological basis for drowsiness remain unclear,” says Masashi Yanagisawa, a pioneer in sleep medicine research who worked as a professor and principal researcher for over twenty years at a top-level U.S. research center, the University of Texas Southwestern Medical Center. Aiming to solve the mysteries of sleep and wakefulness, today he is engaged in a wide range of research activities covering neuroscience, medicinal chemistry, and experimental medicine at WPI-IIIS.
The relation between the deep mysteries of sleep and our internal clock
According to Yanagisawa, the primary factors regulating sleep are our internal clock and homeostasis (our body’s mechanisms for maintaining steady internal conditions). For example, jetlag’s influence on sleep is related to our internal clock, and the powerful drowsiness you feel after pulling an all-nighter is related to homeostasis. Both factors exert a mutual influence, maintaining a certain rhythm for sleeping and awakening. Emotions too affect sleep, such as forgetting sleepiness when excited, or becoming drowsy when bored.
“Our internal clock is a very important factor in sleep regulation,” says Yanagisawa, “and light is the most powerful external factor affecting it. We know that light reaching us at a specific time in the morning advances that clock, while evening-time light conversely slows it. Our retinas have dedicated sensors that detect brightness, and nerve cells in the hypothalamus capture this information to adjust our internal clock. This happens not only with natural light, but any light with a certain illuminance level.”
Careful utilization of this system can allow us to tune our internal clocks. This is why exposure to morning light is often suggested as a way of overcoming jetlag. However, Yanagisawa says that such tuning can shift our clocks by only one or two hours per day at best; it takes one or two weeks to overcome a time difference of ten hours.
“Light itself has wakening effects separate from our internal clock, and light can suppress the secretion of melatonin, a hormone that induces sleep. Therefore, blocking light is an important part of preparing a sleeping environment. It’s best to keep bedrooms dark, such as by sleeping without leaving lights on and using light-blocking curtains.”
Illuminated living spaces make Tokyo a city that never sleeps
Due to the prevalence of shiftwork and night-centered lifestyles, it is said that those of working age in urban areas of Japan get insufficient sleep, and that the Japanese get the lowest average sleep times among developed countries. Modern living environments alone are enough to delay our internal clocks. Looking toward the next 100 years, what will be necessary to adjust our internal clocks to allow for healthy sleep?
“The 2017 Nobel Prize in Physiology or Medicine was awarded for discovery of genes controlling circadian rhythms, and I believe that has led to a dramatic increase in interest in internal clocks. While it may be difficult to suddenly change our lifestyle patterns, I believe that simply being more aware of our internal clocks can help to improve our sleep environments.
“When thinking about future living spaces, we should consider not only the blue light emitted by devices such as personal computers, televisions, and smartphones, but also the significant influence of lighting in the living space itself. Our biological clocks respond to the total amount of light captured by the sensors in our retinas, so being in a room that is brightly lit by fluorescent lights or LEDs at night will mess with our internal clocks more than does looking at smartphones in a dark room. Rooms in Japanese homes are far more brightly lit than are those in Western houses. I hope that we can learn to better control light levels, for example through skillful use of indirect lighting, thereby creating rooms that better adjust our internal clocks.”
We therefore need a shift from “lighting for making rooms brighter” to “lighting for creating and maintaining health.” Following Yanagisawa’s advice, Teijin is investigating spaces that incorporate such internal clock–regulating lighting. Next, we will introduce some futuristic living spaces that make efficient use of light and walls.