In the first and second chapters of Why We Sleep by Matthew Walker, he outlines the two major systems in our brains that contribute to our sleep cycle, as well as the most common chemicals, stimulants, and scenarios in which our sleep either thrives or suffers. He begins by informing his audience of the negative side effects that can occur when we don’t get enough sleep (a full 8 hours each night). These include increased risk of cancer, Alzheimer’s disease, diabetes, cardiovascular diseases, weight gain, and psychiatric conditions such as depression, anxiety, and suicidality, not to mention the more tangible consequences such as drowsy driving and sleep disorders like progressive insomnia. While these are important points to be made, his central focus in the following chapter was more on sleep as a function in our brains: Why do we sleep? What’s really happening when we sleep and what happens when we try to manipulate sleep?
One element of his writing that I found to be particularly interesting was his discussion of our circadian rhythms that originate from the suprachiasmatic nucleus. This particular system in our brains functions as a 24-hour internal biological clock, telling us when exactly we should be awake, asleep, or nearing the phases of entering sleep or wakefulness. During his explanation of the role that Mother Nature most likely played in the pattern of our circadian rhythms, this evolutionary take on the topic made me think of the implications it has in terms of productivity and efficiency. The best example to describe what I am referring to is eating habits.
While this fact remains up for debate to many researchers, it is commonly believed that more frequent smaller meals in a day is more advantageous than eating three large meals at the beginning, midway, and end of the day. It is believed that this leads to metabolic benefits, blood sugar level stabilization, and maximizes energy and nutrients throughout the day. So, if our bodies have the potential to be more productive and energized when we compartmentalize our food intake, could this be the same with our sleep?
Many studies have examined the pros and cons of the different sleep patterns, specifically comparing monophasic, biphasic, and polyphasic. Monophasic is what most would deem the “normal” sleeping pattern of sleeping once during the 24-hour period of a day. Biphasic refers to two sleeping period throughout the day (once through the night and another short period during the day), while polyphasic refers to multiple smaller episodes of sleep throughout the day. This is often employed by people who wish to optimize their time spent awake, like sailors, soldiers, or doctors, but this is generally at the expense of their energy level and productivity.
Several terrestrial mammals that exist today stick to the polyphasic pattern, but for no apparent reason besides body size, pointing to the biological fact that a smaller body mass requires more frequent feeding and therefore shorter, more frequent bouts of sleeping (Capellini, et al., 2008). In other words, polyphasic sleeping patterns, at least in small mammals, result from energy-related constraints. The configuration of sleep for humans follows a general path across our lifespan from the polyphasic pattern of infants to the monophasic and biphasic patterns of adults. While the specific sleep patterns of individuals vary, there are studies which have been conducted to examine exactly what sleep pattern is most optimal for humans, and this depends on a variety of factors such as daily activities, occupation, schooling, and personal preference. One study, published in 2015, examined the sleeping habits of 374 medical students and their performance on a midterm exam based on the sleep they received prior. 38.9% of the students had monophasic, 46.7% had biphasic, and 14.4% had polyphasic sleep patterns. The findings of their cross-sectional survey showed that the majority of the biphasic students (87% to be exact), passed their midterm exam, while only 67.4% of monophasics and 66% of polyphasics respectively passed.
This research provides us with two findings. First, that sleeping in two phases throughout the day (once overnight and another shorter period during the day) is optimal for the circadian rhythm as well as memory (Saeed, Hasan, & Atif, 2015). Second, the biphasic sleeping pattern was the most common among this group of medical students. While this is not necessarily generalizable to the greater population, it is relevant nonetheless because of the lifestyle that medical students maintain and, by extension, the difficulty they experience in finding the time to sleep.
Research such as this confirms that the episodic sleep patterns of polyphasic sleepers aren’t as beneficial as patterns which employ longer sleep phases like monophasic and biphasic, but why is this the case? Many different sources claim different realities of what is best for our bodies, but according to Matthew Walker, 8 consecutive hours is what our bodies should default to even in the absence of awareness of time. Why then, even without needing to deliberately tell our brains that it is time to go to sleep, do we prescribe to lengthier stints of sleep and wakefulness? I can think of only two reasons why this may be the case. The first is that this 24-hour internal clock is simply a product of evolution, as Walker was alluding to, an adaptation that has persisted through the lifetime of most mammalian species on earth. The second is more in regard to the intricacies of sleep itself. For example, if it takes on average 10-20 minutes to fall asleep, does that eat away at a polyphasic sleep schedule which would employ 3-hour sleep phases? Similarly, would these short periods of sleep prevent us from spending enough time in the deeper REM/NREM sleep that we require for our bodies to recover? Further, what is stopping us from exploring this abnormal sleep patterns? While it may not be the optimal strategy for everyone’s specific lifestyles, a habit such as polyphasic sleep could be advantageous in ways we don’t yet realize. Even biphasic sleep, which would involve nothing new besides encouraging people to nap during the day, could prove to be enormously impactful on health and productivity. Perhaps after further research in the field of sleep science, the answers to these questions could be answered.
Saeed, Z., Hasan, Z., & Atif, M. (2015). Sleep Patterns of Medical Students; Their Relationship with Academic Performance: A cross-sectional survey. The Professional Medical Journal, 22(7), 919-923.
Capellini, I., Nunn, C. L., McNamara, P., Preston, B. T., & Barton, R. A. (2008). Energetic constraints, not predation, influence the evolution of sleep patterning in mammals. Functional Ecology, 22(5), 847-853. doin:10.1111/j.1365-2435.2008.01449.x