Monophasic vs. Biphasic Sleep
Most people sleep in a single continuous period each night, referred to as monophasic sleep. Biphasic sleep on the other hand, involves splitting your sleep into two separate segments. This can either consist as one nocturnal sleep period combined with a short daytime nap or as two shorter nocturnal sleep periods.
Cultural and Historical Contexts for Biphasic Sleep
Biphasic sleeping patterns are more common in certain cultures and geographical regions. For example, Spanish cultures often practice a siesta (or “sixth hour”) where businesses close for a few hours in the afternoon and many people will use this time to catch up on sleep. Daytime napping is also widespread across several Asian countries including China and Japan, with a recent survey by the China Sleep Research Society reporting that 72% of Chinese people enjoy a daily afternoon nap.
Some historians have hypothesized that prior to the industrial revolution, biphasic nocturnal sleep may have been the norm across the globe. The theory is that people would typically go to sleep much earlier (i.e., shortly after sunset) before waking up around midnight for a few hours to eat and tend to chores then finally going back to sleep until sunrise. The industrial revolution then introduced an abundance of artificial light, particularly in the early hours of the evening, allowing people to stay awake for longer after sunset. As a result, monophasic sleep started becoming more common until it eventually became the dominant sleeping pattern around the world.
Experiments have found that when participants were placed in settings with less artificial light, many of them would naturally shift towards more biphasic sleeping patterns. Furthermore, analyses of peoples’ brain waves have suggested that midnight waking may even be a pre-programmed aspect of human biology. However, not all researchers agree that biphasic sleep is more natural than monophasic sleep, with some arguing that biphasic sleep is instead driven by external factors such as weather conditions or social habits.
Benefits and Drawbacks of Biphasic Sleep
There is evidence to suggest that biphasic sleep may improve alertness and reduce daytime sleepiness compared to monophasic sleep, particularly in certain individuals such as shift-workers and new parents. Napping studies have also shown that short naps can cause immediate improvements in cognitive performance as well as reduced sleepiness. Further, napping for over 30 minutes can prolong these benefits, although it can also increase the likelihood of experiencing sleep inertia (i.e., a brief refractory period where the brain hasn’t fully woken up yet).
Conversely however, other studies have suggested that daytime napping may negatively impact the quality of subsequent nocturnal sleep, particularly in young children. This raises some concerns about whether biphasic sleeping patterns may be associated with more sleep disturbances compared to monophasic sleep, which could increase the risk of sleep deprivation.
Regardless of whether you sleep in a monophasic or biphasic pattern, the important thing is that you’re getting adequate sleep within a 24-hour period. Ideal sleep duration is still a matter of debate amongst sleep scientists, particularly since it can vary between individuals based on factors such as age and sex (for a recent review on this subject, see our other webstory: “How Much Sleep Should You Be Getting to Stay Young and Healthy?”). However, the general consensus is that you should aim to get at least 6 hours of sleep per day.
References
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Zou D. & Liu S. (2026). Sleep Health: A New Frontier for Public Health. J. China CDC Weekly, 8(12): 325-328. DOI: https://doi.org/10.46234/ccdcw2026.050
Yetish G, et al., (2015). Natural Sleep and Its Seasonal Variations in Three Pre-industrial Societies. Current Biology, 25, 2862-2868. https://doi.org/10.1016/j.cub.2015.09.046
Fagioli I., Barbato G., & Wehr T. A. (2001). Dynamics of electroencephalographic slow wave activity and body temperature during monophasic and biphasic human sleep. Neuroscience letters, 298(2), 83–86. https://doi.org/10.1016/s0304-3940(00)01686-4
Hilditch C. J., et al. (2016). A 30-minute, but not a 10-minute nighttime nap is associated with sleep inertia. Sleep, 39(3), 675–685. https://doi.org/10.5665/sleep.5550
Thorpe K., et al. (2015). Napping, development and health from 0 to 5 years: a systematic review. Archives of disease in childhood, 100(7), 615–622. https://doi.org/10.1136/archdischild-2014-307241
The MULTI Consortium, et al. (2026). Sleep chart of biological ageing clocks in middle and late life. Nature. Advance online print https://doi.org/10.1038/s41586-026-10524-5
