Research Links Sleep Quality to Nighttime Temperature Drops

Investigations involving the Tsimane people of Bolivia, the Hadza of northern Tanzania, and the San of southern Africa revealed that these communities tend to sleep aligned with temperature changes rather than the setting sun. Although these groups do not have electric lighting and predominantly live outdoors, their sleep patterns correspond more closely to the natural fluctuations in temperature throughout the day.

Anthropologist Gandhi Yetish, a contributor to the research, noted that, although light is typically viewed as the primary factor in regulating sleep, temperature changes also stem from sunlight, influencing sleep timing.

The physiological need for body temperature to drop prior to sleep is critical; the core temperature can decrease by approximately 1°C from its peak during the day to a lower level at night. This drop is essential for achieving deep, restorative sleep. A study indicated that participants sleeping in rooms with naturally fluctuating temperatures experienced higher levels of melatonin, which is vital for sleep preparation, compared to those in rooms with constant temperatures. These participants also reported feeling more refreshed in the morning.

Sebastian Herberger, a sleep physician from Berlin, highlighted that many individuals have encountered restless nights due to hot hotel rooms that fail to cool adequately.

Research is also exploring whether temperature influences circadian rhythms, the internal body mechanisms regulating sleep, appetite, and mood. While light exposure has long been viewed as the main driver of these rhythms, emerging studies suggest that temperature changes may play an essential role as well. Some animal studies have shown that temperatures can influence circadian cycles independently.

Preliminary human studies support the idea that cooler room temperatures could help reset body clocks, with findings showing that participants in cooler environments reached their lowest nightly body temperature—a significant marker of their circadian cycle—about an hour earlier than those in constant temperatures. Jerome Siegel, a neuroscientist at UCLA who conducted studies on indigenous sleep patterns, posits that temperature may ultimately be more influential than light and suggests that the modern trend of constant indoor temperatures may contribute to rising insomnia rates in developed societies.

However, not all experts agree. Christian Cajochen, a chronobiologist at the University of Basel, acknowledges temperature as a factor in circadian modulation but calls for more research before it can be considered equally important as light.

For now, a practical recommendation stands out: allowing the bedroom to cool down at night is likely beneficial for improving sleep quality.