A review of the environmental parameters necessary for an optimal sleep environment
Introduction
Achieving sleep of adequate quality and quantity is dependent on an individual having enough time available for sleep at an appropriate circadian phase, with general adherence to basic sleep hygiene recommendations, including sleeping in an environment that is conducive to sleep. Recent consensus reports on sleep need support the notion that adults require 7–9 h of sleep per night [33,117], and studies of sleep and circadian rhythms support the importance of regular sleep timing in positive sleep outcomes [29,100]. Although environmental sleep disrupters are recognized as a contributor to some sleep disorders, the empirical evidence supporting the recommendations on what constitutes an appropriate sleep environment are dispersed over many studies. In addition, there are few resources available to architects and engineers that provide explicit guidance on what characteristics are necessary for designing the optimal bedroom environment. An inappropriate sleep environment can lead to disrupted sleep and reduced sleep quality even in the absence of sleep disorders and when sleep is timed to provide for an optimal sleep opportunity. The goal of this review was to identify the impact of environmental factors on sleep, including ambient noise, temperature, light, and air quality, in order to guide the design of bedroom spaces optimized for healthy sleep.
Section snippets
Methods
We conducted a literature search to identify research papers describing sleep outcomes for the environmental parameters of interest. Given the prevalence of homographs within the search terms of interest (e.g. the terms “light” and “sleep” returned numerous results on “light sleep”), we took a three-tiered approach to include the widest range of literature. We conducted a primary search in PubMed using keywords relevant to each environmental parameter (described below). We conducted a screen of
Noise
Exposure to noise can disrupt sleep quality and quantity [61]. The magnitude of sleep disruption conferred by noise depends on the decibel level (dB), the frequency and pitch, duration (i.e. continuous, intermittent, or impulsive) and whether the noise is meaningful (e.g. a familiar voice). A World Health Organization working group report on noise determined that there is a causal relationship between nighttime noise exposure and self-reported sleep disturbances, use of pharmaceuticals,
Ambient temperature
The relationship between endogenous core body temperature, skin temperature, ambient temperature, airflow and humidity, clothing, and insulation of bedding must all be taken into account when evaluating the impact of temperature on sleep (Fig. 1). Under normal conditions, the circadian rhythm of core body temperature declines just prior to the time of optimal sleep onset and continues to decline throughout the sleep episode, reaching a nadir at approximately 6 h after sleep onset [25,48].
Light
Light leads to sleep disruption due to two factors; first, light resets the circadian pacemaker, leading to a shift in the timing of circadian phase relative to the scheduled sleep episode. Second, light is an environmental stimulus that can cause sleep disruption and night waking. The circadian rhythm is reset by exposure to light through the eyes [22,23,123]. Inappropriately timed light exposure is capable of inhibiting sleep onset and leading to shifts in circadian phase that can impact
Air quality
Poor air quality or gaseous air mixtures that deviate from typical Earth-based sea level air mixtures are capable of causing sleep disruption and impaired breathing during sleep. Exposure to reduced levels of O2 and elevated levels of CO2 can lead to sleep disruption. Ventilatory responses to hypercapnia have been shown to be lower during sleep than during wake [57,91] and a mean value of 3.8% (range 2.3–6.5%) end-tidal CO2 partial pressure has been shown to cause awakening from sleep [30].
Conclusions and research gaps
Sleep is critical to health and daytime functioning. In order for individuals to achieve optimal sleep, they must have access to a sleep environment that allows them to achieve quality sleep, free of external disruption. We found that the optimal sleep environment should be insulated to attenuate intermittent noise, in particular noises above 35 dB. Some evidence suggests that continuous noise may be useful in situations where intermittent noise cannot be eliminated or reduced. More research is
Limitations
Due to the breadth of research on sleep related outcomes, interactions between sleep quality and various special populations were not considered in this review. It is possible that individuals with sleep disorders, for example, may benefit from different environmental conditions than the ones described in the current review. Additionally, although a systematic effort was undertaken to include all relevant articles pertaining to this review, it is possible that some articles were missed in this
Acknowledgements
This study was funded by the Human Research Program at NASA Johnson Space Center (BHP-ARC ITA 14643). The authors wish to thank Lisa Sewall for assistance with obtaining publications for this report, as well as Dr. Durand Begault, and Dr. Brian Smith for providing helpful comments to this review. The authors also wish to thank Renna Bushko, Ravi Chachad, Ann Marie Davidson, Maricruz Esparza, Cindy Hu, Rohit Rao, and Vanessa Real for assistance in collecting literature associated with this
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