Segmented Sleep

Polyphasic segmented sleep, or splitting the night in half with an hour awake, may sound unusual, but preindustrial people practiced this kind of sleep schedule around the world—and for thousands of years. And, although polyphasic segmented sleep fell out of style centuries ago, research indicates that this sleep pattern coupled with an afternoon nap, or siesta, may be ideal for maximizing wakefulness during the day.

So, let’s take a closer look at this unique sleep schedule and see if ancient humans really had it right.

Segmented Sleep History

Early to Bed, Early to Rise

It seems counterintuitive that anyone would (even want to) segment their sleep, wake up in the middle of the night for an hour, and still be productive and alert. But, in preindustrial societies, many people did exactly that—and before alarm clocks too.

During their first segmented sleep, people would’ve rested and recharged from their day’s labor before waking up feeling more refreshed. For this hour or two of wakefulness, many would engage in prayer, meditation, reading, and writing. Or, they could reflect on their dreams which were more easily remembered after a short segmented sleep.
On the other hand, some chose to spend their waking hour being active. It was common to meet with friends, smoke tobacco, and even commit crimes. Furthermore, some medieval doctors even recommended this midnight hour to couples as the ideal time for sex.

Modern Monophasic Sleeping

Although it may feel like people have always been sleeping monophasic, full eight-hour nights, this routine didn’t actually gain popularity until just a few hundred years ago. In fact, research shows that monophasic sleeping began picking up traction with the European upper class during the 17th century and became the norm from there.

Then, in the next few centuries, as industrialization spread across the world, more people began following longer daily work schedules similar to what we have today: eight hours of monophasic rest. By the 1920’s, the polyphasic segmented sleep of the past had become completely replaced with the modern, industrialized sleep schedule.

Sleep Science: Segmented vs. Monophasic

Your Brain on Segmented Sleep

Not all sleep is the same; during the night, your brain and body move through various stages of lighter and deeper sleep. However, for people looking to improve their rest, the most important sleep stages to pay attention to are SWS (Slow Wave Sleep), when your body and muscles recover, and REM (Rapid Eye Movement), when your brain is actively dreaming. While lighter stages of sleep are important too, the more of your sleep you spend in SWS and REM, the more rest you’ll actually get, and the less total sleep you’ll actually need.

Slow Wave Sleep: Typically, sleepers who follow the modern eight-hour sleep experience SWS in cycles throughout the entire night, while segmented sleepers experience more and deeper SWS in their first three hours of rest. 

Rapid Eye Movement: While a monophasic sleeper will sleep through the night, at this point, the segmented sleeper is awakening from their first rest. And, when awake, the segmented sleeper’s brain can begin replenishing its levels of choline. One of the nutrients that influences the brain’s sleepiness and alertness, choline is important for entering deep and restorative levels of REM sleep, and it’s associated with more lucid dreaming too.

Healthy amounts of choline can be found in common foods like animal products and vegetables. However, the segmented sleeper’s brain will replenish its choline to higher levels while awake during the midnight hour. For monophasic sleepers, their secretions of choline just hover around similar levels throughout the night.

Sleep and Hormones

We’ve covered the relationship between the brain and sleep, but let’s take a closer look at the connection between sleep and the body, specifically hormones. But, if you don’t want a whole biology textbook thrown at you, feel free to check out the TLDR at the bottom.

Prolactin: Deeper, more efficient sleep isn’t just about choline levels. During that same waking period, the brains of segmented sleepers also surge with higher levels of the hormone prolactin, which amplifies the feel-good hormone dopamine, suppresses the sex drive, and creates a feeling of calmness and improved rest. 

For monophasic sleepers, however, their brains secrete much lower amounts of prolactin during this same midnight time frame and, instead, secrete it slowly throughout the day. This lack of prolactin during sleep and excess of it during the day can lead to a series of side effects including prolactin resistance, lower libido, early aging, and fat gain too.

Estradiol and Testosterone: One of the primary reasons why the wrong amounts of prolactin secreted at the wrong time can cause these side effects has to do with prolactin’s role in lowering hormones testosterone and raising the hormone estradiol. Testosterone influences libido, especially for men, and fat loss too. On the other hand, estradiol can lead to fat gain in the midsection and chest area for both men and women.

Sleep Science TLDR

Here’s the quick recap on polyphasic segmented sleep and how it affects your brain and body:

• Segmented sleepers get more Slow Wave Sleep during their first rest than monophasic, all-night sleepers.

• When segmented sleepers wake up in the middle of the night, they get a boost of choline and prolactin, hormones that encourage deep sleep.

• After returning to sleep, segmented sleepers get deeper Rapid Eye Movement sleep because their brains have secreted more restful hormones than monophasic sleepers.

• Segmented sleepers secrete more prolactin at night and less during the day than monophasic sleepers. But, prolactin secretion throughout the day is linked to weight gain, higher estradiol, lower sex drive, and lower testosterone.

Sources

Frieboes, R., et al. (1998). Enhanced Slow Wave Sleep in Patients With Prolactinoma. http://www.ncbi.nlm.nih.gov/pubmed/9709935

Harvard School of Public Health (2022). Choline. https://www.hsph.harvard.edu/nutritionsource/choline/

Hegarty, S. (2012). The Myth of the Eight-Hour Sleep. https://www.bbc.com/news/magazine-16964783

Society for Endocrinology (2021). Oestradiol. https://www.yourhormones.info/Hormones/Oestradiol.aspx

Society for Endocrinology (2021). Testosterone. http://www.yourhormones.info/Hormones/Testosterone.aspx

Spiegel, K., et al. (1994). Prolactin Secretion and Sleep. https://pubmed.ncbi.nlm.nih.gov/8191199/

Tsafrir, J. (2021). Segmented Sleep. http://judytsafrirmd.com/segmented-sleep/

Volkow, N., et al. (2012). Evidence That Sleep Deprivation Downregulates Dopamine D2R in Ventral Striatum in the Human Brain. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3433285/

Watson, C., et al. (2011). Neuropharmacology of Sleep and Wakefulness. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3026477/