Biphasic Sleep: What It Is And How It Works

Biphasic sleep describes a pattern of sleep in which a person sleeps in two segments, or phases, per day¹. Although many people sleep for seven or eight hours straight each night, biphasic sleep may be more common than you think.

Biphasic sleeping is practiced by a variety of people across cultures. For example, people who enjoy siestas are considered biphasic sleepers. Some people adopt a biphasic sleep schedule to maximize their productivity. Additionally, many animals are biphasic sleepers, including birds, insects, and mammals². Learn more about biphasic sleep, including how it impacts sleepers.

What Is Biphasic Sleep?

Biphasic sleep is a sleep pattern in which a person splits their sleep into two main segments per day. They may sleep longer at night, and then take a nap during the day. Or, they may split their nighttime sleep up into two segments. Biphasic sleep is also referred to as segmented or bimodal sleep.

Biphasic Sleep vs. Monophasic Sleep

Biphasic sleep is distinct from monophasic sleep, which describes the way most people sleep. In monophasic sleep, a person attains all of their sleep in one block of time, typically at night.

Researchers hypothesize that monophasic sleep became the dominant sleep pattern during the industrial era, when artificial lighting began enabling people to stay up past sunset. Prior to that, many people across different continents and cultures followed a biphasic sleep schedule. They went to bed around 9 p.m. or 10 p.m. and slept for a few hours, before waking around midnight. Then, they would stay up for a few hours to eat, tend to their children, or add wood to the fire. Later that night, they would fall back asleep for their second sleep phase.

As artificial lighting became more common, humans adopted a monophasic sleep schedule. Since then, we have considered ourselves unique among animals for sleeping in a single stretch at night, but we may not be monophasic sleepers after all, according to some research.

In an experiment in the 1990s, a group of healthy participants were placed in a setting in which there was light for 10 hours and complete darkness for 14 hours. This setting contained much less light than our current 16-hour days do. At baseline, participants slept for 7.7 hours at night. Over the course of the study, however, they naturally shifted to a biphasic sleep schedule. In this schedule their sleep took place over an 11-hour period, and they woke up for a one- to three-hour period in the middle of the night.

Our current monophasic sleep patterns might come with disadvantages. Exposure to more artificial light³, especially at night, can decrease melatonin levels and negatively impact our sleep. Plus, some people have natural sleep patterns that resemble biphasic or polyphasic sleep.

Biphasic Sleep vs. Polyphasic Sleep

While biphasic sleepers sleep twice per day, polyphasic sleepers sleep in multiple segments per day.

Polyphasic sleep, which may also be referred to as segmented sleep, describes a sleep schedule with three or more sleep periods per day. Infants are prime examples of polyphasic sleepers, as they sleep multiple times throughout the day.

In adulthood, however, polyphasic sleep can be a sign of a sleep disorder or a neurodegenerative disease like Alzheimer’s⁴ when a person is not sleeping this way intentionally. For example, people with Irregular Sleep Wake Rhythm Disorder have disrupted circadian rhythms that cause them to fall asleep and wake up at random times throughout the day.

Some people intentionally adopt a polyphasic sleep schedule in hopes of becoming more productive. For most people, however, following a polyphasic sleep schedule — particularly one that reduces your total sleep time below the recommended minimum — leads to sleep deprivation and its associated negative physical and mental health outcomes⁵.

Benefits of Biphasic Sleep

Additional research is needed on whether biphasic sleep is better, worse, or about the same as monophasic sleep.

It is worth noting that the original biphasic sleep schedule, which split nighttime sleep into two segments with a waking hour around midnight, was common around the world. This biphasic sleep schedule was the norm even in cultures located near the equator, where residents’ circadian rhythms are not affected by changing seasons. In one case study, researchers found electroencephalographic (EEG) evidence that suggested that the midnight waking hour could be pre-programmed in humans⁶.

Moreover, midday napping has consistently been linked to improved cognitive performance⁷. Shorter naps of 15 minutes or less have been shown to reduce sleepiness and cause cognitive improvements that are felt almost immediately, and last up to three hours afterward. Longer naps lasting more than 30 minutes produce cognitive benefits for a longer time period, but the person has to experience a period of sleep inertia first — that initial grogginess you may feel after waking up.

People who nap regularly, like many biphasic sleepers do, generally enjoy these benefits to a more pronounced effect than those who nap only occasionally.

Biphasic sleep schedules can come naturally to some people. Many of us simply feel more tired in the middle of the day, whether due to a warmer temperature or a big lunch. Some researchers posit the midafternoon slump could be a remnant of our polyphasic sleep schedules in infancy.

Are There Downsides to Biphasic Sleep?

There is a potential downside to biphasic sleep. Some researchers argue that a biphasic sleep schedule is not natural, but due to external factors like our eating habits, social schedules, or hot afternoon temperatures. Further, following a biphasic sleep schedule simply isn’t feasible for some people, such as caregivers or those with strict work schedules. The biggest issue with biphasic sleep, though, is the potential for sleep deprivation.

Sleep deprivation can result from poor sleep quality and insufficient sleep overall. Chronic sleep deprivation can increase your risk for serious health problems⁸ like heart or kidney disease, diabetes, stroke, high blood pressure, obesity, and depression. Sleep-deprived children may exhibit hyperactivity or attention problems, in addition to poorer school performance. Sleep deprivation also increases risk of injuries and drowsy-driving accidents.

In addition to the physical consequences, sleep deprivation impairs cognitive performance. Studies of preschool-aged children have found that daytime napping reduces attention span⁹ and vocabulary. Further, the children studied slept less at night due to napping during the day, and they were more likely to make errors on a test. Other studies of young children have found that daytime napping correlates with poor sleep quality¹⁰, which could have negative developmental impacts.

What Is a Biphasic Sleep Schedule?

A biphasic sleep schedule is any sleep schedule that involves two sleep periods per day. Common variations of biphasic sleep schedules include:

• Siesta Sleep Schedule: In many parts of the world, most notably Spain and Italy, residents take a 60- to 90-minute siesta during the day. This nap usually occurs in the afternoon, and people then only sleep for five to six hours per night.
• Midday Nap Sleep Schedule: With this biphasic sleep schedule, people swap the long siesta for a short, 20- or 30-minute nap during the day. At night, they sleep longer, such as for six or seven hours per night.
• First/Second Sleep Schedule: The original biphasic sleep schedule, from the preindustrial era, split sleep into two segments during the night. People would have their first sleep around 9 p.m. or 10 p.m., wake up around midnight for an hour or two, and then have their second sleep after that.

With each biphasic sleep schedule, the person should still obtain a total of at least seven hours of sleep per 24-hour period.

Tips for Starting Biphasic Sleep

If you are interested in trying a biphasic sleep schedule, there are steps you can take that may help make the transition successful.

Choose a Biphasic Sleep Schedule

Start by deciding on a biphasic sleep schedule you want to try. Then, set a morning wakeup time, so you can schedule your nap or bedtimes accordingly to allow for at least seven to eight total hours of sleep.

For example, if you choose the first/second sleep schedule and your wakeup time is 8 a.m., you would need to go to bed for your first sleep around 10 p.m. You could sleep until 2 a.m., wake up for an hour or two, and go back to sleep for another four hours to wake up at 8 a.m.

If you decide on a siesta sleep schedule, and your wakeup time is 6 a.m., you could go to sleep at 11 p.m. or midnight, and schedule another hour of sleep during your midday nap. When creating your biphasic sleep schedule, be sure to schedule your nap around the midafternoon. This time is preferred because taking a nap later in the day, especially a long nap, has the potential to disrupt your sleep later that evening.

For best results, follow your new biphasic sleep schedule for at least a week. It takes time to adjust to a new bedtime, let alone a whole new sleep schedule. Schedule your meals accordingly in order to help your body adjust.

Stay Consistent

As you get used to a biphasic sleep schedule, be diligent about maintaining consistent bed and wake times. Not only will following a regular sleep schedule make it easier for you to adjust, but going to sleep and waking up at inconsistent times is associated with poor long-term health outcomes, like a greater risk¹¹ of cardiovascular disease, obesity, hypertension, and diabetes.

Limit Your Light Exposure

Starting 30 to 60 minutes before you sleep or take a nap, reduce your exposure to artificial light. Artificial light includes the light from phones, televisions, computers, and tablets. It also helps to dim lamps and overhead lights.

If you follow a first/second sleep schedule, avoid using bright lights during your waking hour. Wear blue light blocking glasses, use dim light bulbs with reddish or yellowish hues, and turn on your phone’s night mode setting.

Practice Good Sleep Hygiene

Sleep hygiene refers to the habits and practices you have around sleep. The following habits can help improve your sleep hygiene, regardless of your sleep schedule.

• Stick to a regular sleep schedule for both your sleep periods. Your nap should take place around the same time every day, and so should your nighttime sleep.
• During the day, eat well and exercise.
• Keep your bedroom dark, quiet, and cool.
• Avoid using your bed for anything other than sleep and sex.
• Limit your caffeine intake, and avoid having any for a few hours before sleep.
• Avoid electronics and artificial lights at least 30 to 60 minutes before sleep.
• Follow a calming bedtime routine to relax before going to sleep.

Monitor Your Results

Changing your sleep schedule can feel drastic, and biphasic sleep is not for everyone. Pay attention to how you feel throughout the process. Determining whether you feel more alert and focused, or more groggy after shifting your schedule can help you decide if biphasic sleep is for you.

What Kind of Sleep Is Best for Me?

Some people find that biphasic sleep feels natural and works great for them, while others feel better on a monophasic sleep schedule.

There is historical evidence that humans used to naturally follow a biphasic sleep schedule. Research has also proven the benefits of a short, midday nap. If you would like to experiment with biphasic sleep, a 20-minute nap during the early afternoon might be one way to ease into it.

Because sleep is essential to our overall well-being, it may be beneficial to talk with your doctor before radically changing your sleep schedule. They can offer additional recommendations for improving your sleep quality and daytime energy levels.