Did You Know Humans Used to Sleep in Two Phases? Here’s Why We’ve Moved on From the Practice

By: SleepScore Labs  |  April 8th, 2022

Electricity came, and humans had to adjust their sleep patterns accordingly.  

But before that time, some parts of the world slept in two phases within a 24-hour span. It was common practice in some populations to have “two sleep periods”; you could have the first snooze during the day and the second at night. Or have the first from evening to midnight, and the second from the earlier morning hours to daybreak. 

Nowadays, it’s clear the volumes of research that support the benefits of sticking to one round of sleep in a day, known as monophasic sleep, and to steer clear of multi-phase sleep patterns. Recent studies show that sleeping in multiple phases within a 24-hour period may adversely affect physical and mental health, and it’s widely not recommended for most people.  

But, it’s fascinating to learn how sleeping in two phases came to be, why it left our daily practices, and why experts agree that, for most healthy people, this kind of sleep schedule that distributes sleep across multiple periods over a 24-hour period is not recommended.  

Getting to Know Polyphasic and Biphasic Sleep 

Sleeping in two phases, also known as biphasic, diphasic, bimodal, or segmented sleep, is a sleep pattern where a person gets two sleep periods in a day.  

According to historians, this sleep pattern is unpopular in the 21st century. However, this kind of sleep schedule was more widely adopted before the late 19th century, when Thomas Edison invented the light bulb, allowing humans to enjoy more activities late into the evening, thereby pushing their bedtimes later. 

Generally, experts recommend getting seven or more hours of sleep once a day to support daytime functioning and optimal health and reduce the risk of chronic illnesses like diabetes, heart disease, depression, and stroke. This modern sleeping pattern is known as monophasic sleep. 

Another form of sleep pattern is polyphasic sleep. This sleep pattern involves having more than two sleep segments a day. Studies suggest that this sleep pattern is popular among students and workers who want to maximize their daytime functioning.  

However, polyphasic sleep has been linked to excessive daytime sleepiness and may result in poor physical, mental, and emotional health. Experts, therefore, do not recommend this sleeping habit.  

History of Sleeping in Two Phases 

Anthropological studies suggest that sleeping in two phases used to be the norm.  

Centuries ago, before the industrial era, people in many parts of the world, including Europe, Africa, North America, South Asia, Latin America, the Middle East, and Australia, followed a segmented sleep pattern. 

As the sun went down, people would usually complete their tasks to have their first sleep. After about four hours, they’d wake up and participate in various activities, including house chores, visiting neighbors, telling stories, or talking about their dreams. 

The BBC even mentions that a doctor’s manual from the 16th century in Frances recommended that couples have sex after the first sleep because it was the “best time to conceive”, noting that they could „have more enjoyment“ with this approach. 

These activities between the sleep sessions usually lasted for an hour before everyone went back to bed.  

This unique practice continued until the late 19th century when Thomas Edison invented the light bulb.  

How did the light bulb disrupt this sleep pattern? This discovery allowed people to carry on work till the later evening hours, be more productive, or enjoy nighttime activities. In doing so, they dropped the first sleep, went to bed later, and had adopted one long sleep shift in favor of two shorter ones. 

Interestingly, research shows that non-western cultures like West Africa and Southern Africa, which had no electricity, also continued this two-phase sleep practice until the late 19th century. 

Additionally, some modern cultures still partake in biphasic sleep, but in the form of a nap, usually less than an hour, in the middle of the day. This sleeping habit is widespread in Spain, Italy, China, and Scandinavian countries like Finland, Denmark, and Sweden.  

In fact, in 2015, the Mayor of Ador, a small town in Valencia, ordered a compulsory afternoon three-hour nap, where businesses close and everyone takes a break or rests from 2 pm to 5 pm.  

How Sleeping in Two Phases Works 

As the name suggests, sleeping in two phases involves having two sleep periods in a day. Having divided sleep may impact a person’s alertness, performance, and mood during the day.   

Sleeping in two phases may occur in two ways: 

  • Two sleep sessions at night 

The first sleep session usually starts in the early evening and lasts through midnight. The second begins after midnight and ends in the morning. 

  • One sleep session during the day and at night. 

The first sleep session could be less than an hour but not longer than three hours. The second sleep session is usually for 7 hours or more.  

The second type of biphasic sleep is still prevalent in today’s world. People take naps (or siestas, a practice in Spain and Italy) in the middle of the day to refresh and reenergize for a productive rest of the day.  

Are There Benefits to Sleeping in Two Phases? 

This biphasic sleep pattern hasn’t been extensively studied in sleep science. Many experts describe healthy sleep in reference to monophasic sleep, requiring adequate duration, uninterruptedness/continuity, and intensity.  

Although people may have benefitted from sleeping in two phases when it was still a popular practice, there’s no evidence that this may be the case for life in the 21st century. Waking up in the middle of the night and partaking in some activities before having a second sleep may disrupt your nighttime rest, reducing your chances of getting the needed time in each restorative sleep stage.  

In today’s world, if people were to wake up to work or play for an hour, it would likely involve using electronic devices which emit blue light. This wavelength of light is known to trigger alertness and stress hormones called cortisol, making it harder to fall back to sleep. 

Research also suggests that exposure to blue light may impair the circadian rhythm, the body’s clock that regulates the sleep-wake cycle, and other biological processes in the body. This impairment is associated with other severe health consequences like obesity, diabetes, heart diseases, blood clotting, and inflammation. 

On the other hand, taking a midday nap for 10 minutes, but not more than 30 minutes, is associated with increased productivity, alertness, and performance. Sleeping for longer than 30 minutes may lead to sleep inertia, a condition where a person feels groggy, disoriented, and sleepy.  

If you’re having trouble getting enough sleep at night and are considering trying the biphasic sleep pattern, it’s best to consult with a physician first to determine whether sleeping in two phases may be ideal for you. Monophasic sleep – or one main nighttime sleep period – is overwhelmingly recommended for most healthy people. Other treatments or lifestyle interventions may be the ideal first line of defense before trying something as unusual as biphasic sleep.