It’s a bird! It’s a plane! It’s…a starfish? Perhaps you’ve fallen asleep with a loved one or a friend who was sprawled out on their back, sound-asleep. If asked to describe the position that you tend to sleep in, you would likely be able to do so; have you ever wondered why you might have such a preference? Regardless of whether or not you prefer to sleep like a fetus or a starfish, our sleeping position changes approximately 1.6 times per hour while we are asleep (Skarpsno, Mork, Nilsen, & Holtermann, 2017), causing our bodies to be arranged in many positions throughout the night. Is it possible that our body positioning during periods of sleep have the ability to help or harm our sleep experience? The answer may be yes. 

Body movements ranging from minor muscle twitches to larger-scale movements, such as a shift in sleeping position, may occur during sleep. Most of our movement happens while we’re in non-rapid eye movement (NREM) sleep stage 1, during which we can be easily awakened, whereas movement is less likely to occur during deeper sleep of NREM stages 3 and 4 (Wilde-Frenz & Schultz, 1983). Although slight movements can occur during rapid eye movement (REM) sleep, larger movements are unlikely due to the presence of muscle atonia; during this state, muscle tone is greatly decreased and the brain stem transmits signals down the length of the spinal cord to restrict muscle movement in areas such as the arms and legs. Have you considered that even though we probably wouldn’t choose to have our arms and legs pinned down while we’re awake, we’re A-OK with it while we’re asleep? Many of us may use playful terminology to refer to sleeping positions (e.g. fetus, starfish, log, freefaller), but the convention among sleep researchers is to categorize sleep positions as supine (lying on your back), prone (lying on your stomach), left lateral (lying on your left side), and right lateral (lying on your right side). 

The impact of body position on sleep quality has been widely explored among people suffering from obstructive sleep apnea (OSA), a sleep disorder in which breathing periodically stops and resumes (Mayo Foundation for Medical Education and Research, 2021). Between 65% and 87% of individuals who suffer from mild or moderate OSA display breathing problems when sleeping in the supine position, and notably, have experienced improved sleep quality after shifting to their side (Oksenberg & Gadoth, 2014). It is worthwhile that researchers have dedicated lots of attention to the ways in which sleeping positions influence sleep quality among those with OSA, but much less research has looked at the relationship between sleep position and sleep quality among people without sleep disorders. 

Skarpsno and colleagues (2017) aimed to address this by studying the sleeping positions of 664 men and women who not only did not have a sleep disorder, but who also had no history of  psychiatric disorders or substance abuse which have been linked to disrupted sleep (Walker, 2017). Over the course of approximately six nights, participants wore a small device that measured their sleeping position and body movement; at the end of the study, researchers found that participants spent 54.1% of their time asleep on their side, 37.5% of their time asleep on their back, and 7.3% of their time asleep on their stomach.

There were also age differences in sleeping positions: the amount of time spent sleeping on one’s back decreased with age whereas time spent sleeping on one’s side increased with age! Sex differences in body position during sleep have also been found among college students; based on subjective reports of sleeping positions, women appear to spend more time sleeping on their right side as opposed to on their backs, and men tend to sleep on their backs more often than on their right side (Arbinga, 2018). In terms of sleep quality, Arbinga (2018) also found that students who reported sleeping mostly on their backs scored the highest on measures of anger in comparison to right and left side sleepers. 

It’s common for scientists to use the Pittsburgh Sleep Quality Index (PSQI)—a questionnaire that asks about typical sleep habits over the past month—to evaluate a person’s subjective sleep quality. A study of right and left side sleepers used the PSQI to explore whether or not sleep quality differed between these sleeping positions (Agargun, Boysan, & Hanoglu, 2004). People who slept on their right side reported having better sleep quality in comparison to left side sleepers and interestingly, the left side sleeping position was associated with the occurrence of more nightmares than the right side position. 

Subjective accounts of sleep quality are useful especially when researchers are examining the sleep quality of hundreds of participants—it is much less feasible to study sleep positions of such a large number of participants within a laboratory. Despite this, relying on subjective measures of sleep quality alone may call into question the accuracy of participants’ responses (I don’t know about you, but I struggle to remember most of my physical or psychological behavior from one night’s sleep, let alone during the past month!), so objective measures are needed to support self-reports of the relationship between sleep position and sleep quality. 

Typically, objective evaluations of sleep quality include a person’s sleep onset latency (the amount of time it takes to go from wakefulness to the first period of NREM or REM sleep), the amount of time they spend in each sleep stage, and their total sleep time. Based on these measures, people who mainly sleep on their right side and on their back have been found to spend more time in deep sleep (Ozcelik et al., 2015). Using EEG and fMRI recordings, Xu and colleagues (2020) found that sleeping on one’s back was also associated with a shorter sleep onset latency than experienced by people who slept on their side. This may mean that if you want to fall asleep faster and remain in deep sleep for longer, lying on your back might be your best bet! Also, lying on one’s stomach has been linked to reduced sleep quality potentially by forcing the sleeper to exert more energy to breathe (Skarpsno et al., 2017). 

The answer to whether or not there is one sleeping position that maximizes sleep quality cannot be given in terms of black and white. For example, sleeping on your back might allow you to fall asleep faster and spend more time in deep sleep, but it could also mean that you might wake up more irritable. Would you choose this trade-off? Nevertheless, a causal relationship has not been extensively drawn between sleep positions and sleep quality, particularly among those not suffering from OSA, so feel free to embrace whatever sleeping positions suit you! At least for now.

References

Agargun, M. Y., Boysan, M., Hanoglu, L. (2004). Sleeping position, dream emotions, and subjective sleep quality. Sleep and Hypnosis, 6(1), 8-13. 

Arbinga, F., Tornero-Quiñones, I., & Fernández-Ozcorta, E. (2018). Sleeping position, expression of anger and subjective sleep quality in university students. Sleep and Hypnosis, 20(4), 267-274. doi: 10.5350/Sleep.Hypn.2018.20.0161

Mayo Foundation for Medical Education and Research. (2021). Obstructive sleep apnea. Retrieved 27 February 2021, from https://www.mayoclinic.org/diseases-conditions/obstructive-sleep-apnea/symptoms-causes/syc-20352090 

Oksenberg, A. & Gadoth, N. (2014). Are we missing a simple treatment for most adult sleep apnea patients? The avoidance of the supine sleep position. Journal of Sleep Research, 23(2), 204-210. doi: 10.1111/jsr.12097

Ozcelik, H. K., Bayram, M., Doganay, E., Kart, L., Sezer, M., Akkoyunlu, M. E., Karakose, F., & Yakar, F. (2015). Effects of body position on sleep architecture and quality in subsyndromal adults without apparent obstructive sleep apnea. Sleep and Biological Rhythms, 13, 279-286. doi:10.1111/sbr.12116

Skarpsno, E. S., Mork, P. J., Nilsen, T., & Holtermann, A. (2017). Sleep positions and nocturnal body movements based on free-living accelerometer recordings: Association with demographics, lifestyle, and insomnia symptoms. Nature and science of sleep, 9, 267–275. https://doi.org/10.2147/NSS.S145777

Walker, M. (2017). Why we sleep: unlocking the power of sleep and dreams. Penguin Books.

Wilde-Frenz, J. & Schultz, H. (1983). “Rate and distribution of body movements during sleep in humans.” Perceptual and Motor Skills, 56, 275-283. https://doi.org/10.2466/pms.1983.56.1.275Xu, D., Chen, X., Tian, Y., Wan, X., & Lei, X. (2020). Lying posture affects sleep structures and cortical activities: A simultaneous EEG-fMRI imaging of the sleeping and waking brain. Brain Imaging and Behavior. https://doi.org/10.1007/s11682-020-00413-4

Source of Featured Image: MIT News