Sleep is the physiologically dormant part of our daily lives, which cycles through stages of brain activity of which the most important is REM (Rapid Eye Movement). (American Sleep Association 2017). Sleep is a crucial part to keep physically, socially, and mentally healthy. When sleep is hindered, a variety of sleep disorders develop such as insomnia, sleep apnea, to name a few. A recent study has found a correlation between sleep, and the hours of sleep to the increased temperature, and this trend will increase with time due to climate change(Obradovich et. al. 2017).

Effects of temperature on sleep and sleep disorders have been researched as early as 1996. A study with the sleep disorder center tested passive body heating on quality of sleep. The experiment focused on treating sleep disorders suffered by people who routinely experience fragmented sleep by introducing passive body heating via hot and lukewarm baths (Dorsey et. al. 1996). There were 13 subjects tested over a two-week period who were introduced to hot bath and lukewarm bath conditions (40 degrees Celsius ° and 38 degrees Celsius ° on average respectively) 90 minutes prior to sleep and tested internal core temperatures in response to the bath.Confounding factors such as medication, age, and caffeine were consideredand adjusted accordingly with guidelines strictly followed. The results concluded that patients experienced less interruptions in sleepnwhen taking a hot bath prior to sleep, but tests on sleep efficiency were neither tested nor considered. 

With little recorded data correlating temperature internally and sleep deprivation, there has been research shifted towards the effects of ambient temperatures. One of the earliest studies conducted on ambient temperatures and sleep by Freedman was published in 2006 in the Journal of the North American Menopause Society, which researched REM sleep, hot temperatures, and sleep disturbances (Freedman et al. 2006). The study was quite unusual, and does not represent an entire population but was focused on 18 postmenopausal women with hot flashes, and 18 more women either cycling or no hot flashes reported. The experiment was conducted over a 4-day observational period of sleep. Observations first reported that hot flashes, or excessive heat dissipation, in the subjects followed awakenings. The following results from the experiment found that less hot flashes occurred on nights that were cold, which in turn resulted in less arousals and awakenings.It should be noted as well by the study that thermoregulation is absent during REM sleep, thus hot flashes would not be produced during this cycle of sleep. The study’s data overwhelmingly found that warmer nights found warmer skin temperatures, and increased ambient temperatures correlated to increase arousals and awakenings. Although sleep disturbance increases with temperature, it appears that REM sleep is not affected.

The second study by Freedman appears contradictory to what was reported by Dorsey et. al., but the newest study by Obradovich et. al. (2017) using US data by the University of California – San Diego, could further enlighten on this the effects of ambient temperatures on sleeping. The study addressed the changes in the climate, specifically rising temperatures and how they have affected sleep patterns in people across the United States. Using data on the US, it represented the largest study of its kind and the first to apply the effects of climate change. The experiment focused on 765,000 Americans, comparing self-reported insufficient sleep and data on daily temperatures across the US for an entire year between 2010 to 2011. The results found that an increase in temperature as much as one degree Celsius °was the equivalent of three nights of insufficient sleep per 100 individuals per month. In addition, the results also found that the effect was not equivalent across all levels of income or age, with those earning less than $50,000 a year and those over 65 were most severely affected.

Further results of the study compared the results to NASA Earth Exchange information on temperature and climate in 2050 and 2099. The data resulted in as much as 6 nights of insufficient sleep per 100 individuals per month and up to 14 nights of insufficient sleep per 100 individuals per month for the years researched, respectively. These results although speculative, raise concerns for the future and the effects of sleep.

The data of the compiled research is not representative of all research completed on this topic, but the data has shifted over time and moving towards evidence on the positive correlation between increased temperature and insufficient sleep. When looking holistically on the effects of this data, it is important to acknowledge climate change and the shift towards increasing temperature, as well as how this may affect future sleeping patterns. 

 

COPYRIGHT: This article is property of We Speak Science, a nonprofit institution co-founded by Dr. DetinaZalli (Harvard University) and Dr. Argita Zalli (Imperial College London). The article is written by Antonio Del Vecchio (Cornell University, Division of Nutritional Sciences).

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