Effects of thermal environment on sleep and circadian rhythm

Abstract

The thermal environment is one of the most important factors that can affect human sleep. The stereotypical effects of heat or cold exposure are increased wakefulness and decreased rapid eye movement sleep and slow wave sleep. These effects of the thermal environment on sleep stages are strongly linked to thermoregulation, which affects the mechanism regulating sleep. The effects on sleep stages also differ depending on the use of bedding and/or clothing. In semi-nude subjects, sleep stages are more affected by cold exposure than heat exposure. In real-life situations where bedding and clothing are used, heat exposure increases wakefulness and decreases slow wave sleep and rapid eye movement sleep. Humid heat exposure further increases thermal load during sleep and affects sleep stages and thermoregulation. On the other hand, cold exposure does not affect sleep stages, though the use of beddings and clothing during sleep is critical in supporting thermoregulation and sleep in cold exposure. However, cold exposure affects cardiac autonomic response during sleep without affecting sleep stages and subjective sensations. These results indicate that the impact of cold exposure may be greater than that of heat exposure in real-life situations; thus, further studies are warranted that consider the effect of cold exposure on sleep and other physiological parameters.

Shift-Work Disorder and Sleep-Related Environmental Factors in the Manufacturing Industry

“…We hypothesized that the environment (temperature and humidity, brightness, noise, smell) in which one tries to fall asleep may induce SWD, as several reports have associated these factors with sleep [21][22][23][24][25][26][27]. For example, temperatures under 21°C and above 29°C have been associated with arousal during sleep [21].…”

“…For example, temperatures under 21°C and above 29°C have been associated with arousal during sleep [21]. Humidity has been correlated with increased wakefulness and decreased slow-wave sleep and rapid eye movement (REM) sleep [22], and brightness has been reported to cause awakening [23], melatonin inhibition [24], high body temperature [25], and stimulation of the sympathetic nervous system [26]. Noise also reduced slow-wave sleep and REM sleep [27].…”

Local body cooling to improve sleep quality and thermal comfort in a hot environment

“…3,4 The thermoregulatory system and the sleep regulating mechanisms have been shown to be strongly linked in humans, 5,6 and this was later confirmed by many studies that show high or low air temperatures, even moderately different from the neutral temperature, could significantly decrease sleep quality. [7][8][9][10] However, in many areas with long and hot summers, indoor air temperatures are very high. For example, in southern China, the indoor air temperature was found to be higher than 34°C in natural ventilated buildings during the summer season.…”

Temperature and Humidity Effects on Hospital Morbidity in Darwin, Australia

“…This variability can be seen for the 1945 to 2015 period with monthly mean morning (9 AM) conditions varying from 23 C to 30 C, and relative humidity varying from 60% to 83%; whereas afternoon (3 PM) conditions varied from 30 C to 32 C and 37% to 72% relative humidity. Significantly, these seasonal trends in temperature and relative humidity are not in phase, resulting in annual temperature maxima that occur 3 months before annual relative humidity maxima.…”