Sleep Expert Recommends Continuous Air Conditioning for Summer

Professor Masashi Yanagisawa of the University of Tsukuba recommends using air conditioning continuously until morning to improve summer sleep quality ^[1].

Maintaining a stable environment is critical because heat significantly disrupts the quantity and quality of rest, affecting overall health and productivity. Seasonal data indicates that 69% of people struggle with sleep during the summer ^[2], the highest proportion of any season.

Yanagisawa, a recognized authority on sleep science, suggests a specific bedroom environment to optimize rest. He recommends setting the room temperature to approximately 24C ^[1] and keeping humidity levels between 50% and 60% ^[1].

"Air conditioners should be used continuously until morning," Yanagisawa said ^[1]. This contradicts the common practice of using timers that shut off the cooling system mid-sleep, which can lead to awakenings as temperatures rise before dawn.

While summer presents the greatest challenge, sleep disturbances persist throughout the year. Data shows that 48% of people struggle in winter, 47% in spring, and 40% in autumn ^[2]. Yanagisawa said that while he lowers the temperature slightly in winter, the adjustment is only by two to three degrees ^[1].

Proper climate control is not merely a matter of comfort but a necessity for cognitive function. In Japan, the economic loss resulting from sleep deprivation is estimated at approximately 15 trillion yen ^[3]. This systemic issue is often exacerbated by a lack of understanding regarding sleep debt and recovery.

Yanagisawa's guidance emphasizes that the body requires a consistent thermal environment to remain in deep sleep cycles. By avoiding the temperature spikes associated with timer-based cooling, sleepers can avoid fragmented rest and the subsequent daytime fatigue that contributes to the aforementioned economic losses ^[3].