How Environmental Factors Impact Sleep

How Environmental Factors Impact Sleep

By Ryan Neely, Ph.D.

It should come as no surprise to anyone that our sleep environment impacts how well we’re able to sleep. Anyone who has lain awake during a sweltering summer night or tossed and turned while the upstairs neighbors…practice clog dancing? Or are they bowling? We instinctively understand that the optimal sleep environment is one that’s quiet, dark, and just the right temperature. But what exactly is the right temperature; how dark should our room be, and how do we know? In this post, we’ll highlight a few studies that set out to answer these questions, and summarize what they found. Specifically, we’ll focus on 3 environmental factors:

1. Light
2. Sound
3. Temperature

Hopefully, by the end of this post you’ll have a better understanding of how your environment impacts your sleep, and have a sound scientific argument why those neighbors should stop… whatever it is that they’re doing up there!

Light: It turns out that there are a couple factors to consider when studying the impact of light on sleep. The first consideration is obvious: overall brightness, or how much light is in the room when trying to sleep. The first study we’ll discuss examined the impact of light on cardiometabolic function (Mason et al., 2022). This study is particularly interesting, because instead of only measuring typical sleep architecture such as sleep efficiency and time in each sleep stage, the authors went even deeper and measured analogs of sympathetic nervous system activation and glucose metabolism. In this study, 20 healthy adults slept in a sleep lab for 2 nights: 1 night with some ambient light, and 1 night in darkness, or 2 nights just in dim light. For reference, the “light” condition was set to 100 lux, a measure of brightness, which is roughly the brightness of a dark, overcast day. The dark condition was 3 lux. 

Unsurprisingly, the researchers observed differences in sleep architecture when participants spent the night in the light condition, with significantly less time spent in sleep stage N3 (deep sleep) and REM, and a greater amount of time spent in light sleep (N2). However, they also observed significant differences in insulin resistance (about a 15% increase), and a greater insulin spike response 30 minutes after administration of glucose. These measures suggest that the sleep deficits caused by the room light impacted participants’ metabolisms in a negative way. Additionally, the researchers also observed an increase in heart rate during sleep, and a change in the low-frequency/high-frequency ratio of heart rate variability: taken together, these changes suggest an increase in cardiometabolic stress.

The other factor to consider is the type of light you’re exposed to: you may have seen blue light filter options on your screen-bearing devices and wondered what that’s all about. The answer has to do with a peculiarity of light-sensitive cells in your eyes. Thinking back to science class you may recall that your eyes have light-sensitive rods (dim light, black and white vision) and cones (bright light, color vision). These cells rely on light-sensitive proteins called rhodopsins which detect the presence of light. It turns out that there is an additional class of light sensitive cells in the eye, called intrinsically photosensitive retinal ganglion cells (or ipRGCs). These cells don’t contribute to vision - instead, they detect light in order to help regulate the wake-sleep cycle. Additionally, they use a different kind of light-sensitive protein called melanopsin, which you might have guessed is responsible for regulating melatonin, a sleep-regulating hormone. Activating melanopsin suppresses melatonin production, helping you stay awake during the daytime. Unlike the rhodopsins in your rods and cones, melanopsin is optimally sensitive to blue light, meaning that maximum suppression of melatonin (and therefore sleepiness) occurs when these ipRGCs are hit with blue light. Unfortunately, LCD displays in things like computers and cell phones produce a lot of blue light, which is why all of that scrolling can contribute to poor sleep. 

Sound: There are few things more jarring than being abruptly woken up by a loud noise in the night. But, there are also plenty of sounds that you may just sleep right through. In fact, many people may even prefer some level of background noise while sleeping, such as a white noise machine or an overhead fan. So what does the data say? Interestingly, the World Health Organization (WHO) has weighed in on this topic and given specific guidance about just how much noise should be allowed in urban environments to prevent occupants’ sleep. Their recommendations include two numbers: first, a maximum baseline sound level, which is meant to represent continuous background noise. According to the WHO, this type of noise should not exceed 30 dB. For reference, that’s about the volume of a whisper, leaves rustling, or soft music. A typical white noise machine probably falls into this category. Additionally, the recommendations also specify a maximum value of noise peaks - temporary jumps in sound volume that could disturb a sleeper. These should not exceed 40 dB, which is about the sound level of light rain or birds chirping. Interestingly, a study of ICU patients (who desperately need quality sleep) found that these sound level changes are the most likely to disrupt sleep regardless of the background sound levels (Stanchina et al., 2005). The researchers found that sound level changes of 17.5 dB (from any baseline) were most likely to cause awakenings. This is roughly the equivalent of the sound of 2 people speaking being interrupted by a vacuum cleaner. Put that way, it’s not hard to imagine how that would be disruptive!

Temperature: Many physiological variables cycle with the circadian rhythm, one of which is temperature. In a constant temperature environment, body temperature is at its lowest during the early morning hours, and peaks in the afternoon. Most people have experienced sleep disruption due to discomfort from a room being too hot or too cold, so how do these variables interact, and what is the best temperature for healthy sleep? The WHO has weighed in on this topic, too. They recommend a minimum air temperature of 18℃ (64.4 ℉) during sleep. Another group that thinks a lot about building conditions, the Chartered Institute of Building Services Engineers (CIBSE) recommends a temperature range of 17-19℃ for bedrooms (62-66 ℉) in winter and 23-25℃ (73-77 ℉) in summer. Interestingly, a separate study of sleepers that measured room temperature and sleep quality (Xiong et al., 2020) found no correlation between the measured temperature of a room and participants’ perception of whether the room is too hot or too cold. The authors suggest that there are a lot of factors that can influence personal preference of room temperature, including the clothes and bedding one uses. However, they did find a negative association between room temperature and sleep quality, with a 1% decrease in sleep efficiency for every 1 degree increase in bedroom temperature. Is there an optimal temperature profile to enhance the effectiveness of sleep? For the most part, it appears that the optimal temperature might be somewhat personal preference, as long as it’s not too hot or too cold. However, one study did find that a fall-rise temperature cycle (in which the temperature starts warm at the beginning of the night, decreases towards the middle of the night, and rises again in the morning) did result in better next-day performance (Lan et al., 2016). However, they didn’t find any significant differences in comfort or sleep quality.