What Is Biphasic Sleep? A Complete Guide

Sleep is essential for physical health, mental functioning, and emotional well-being. Most people today aim for a single long period of rest at night — known as monophasic sleep — but alternative sleep patterns like biphasic sleep are common in many cultures, environments, and even in our evolutionary past.

Defining Biphasic Sleep

Biphasic sleep refers to sleeping in two distinct segments within a 24-hour period.

In contrast:

• Monophasic sleep: One uninterrupted block of sleep per 24 hours (the norm in many modern societies).

• Polyphasic sleep: More than two periods of sleep per 24 hours.

Examples of biphasic sleep include:

• A longer main sleep at night (~5–7 hours) and a daytime nap (often 20–90 minutes).

• Segmented sleep, where sleep is divided into two periods during the night with a wakeful break in between.

Alternative terms you might see include bimodal, diphasic, segmented, or divided sleep.

How Biphasic Sleep Works

To understand biphasic sleep, it helps to grasp how sleep normally works. According to research summarized by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD):

• Sleep cycles through non-REM and REM stages multiple times per night.

• Each cycle serves important functions — deep sleep supports physical restoration and hormone regulation, while REM sleep is critical for memory, emotional processing, and learning.

Traditional biphasic sleep does not change the biological stages of sleep — it simply splits sleep into two chunks, each of which proceeds through these stages.

Typical Biphasic Structures

Here are common ways people implement biphasic sleep:

• Night + Nap:

  • Example: 6–7 hours of sleep at night + 20–90 minute nap in the afternoon.

  • This is common in cultures with siesta traditions.

• Segmented Night Sleep:

  • Example: Sleep early evening, wake for 1–3 hours, then sleep again until morning.

  • Researchers propose this may reflect how humans naturally slept before industrialization.

The History

Most people today sleep in one continuous block, but historical evidence suggests that multipart sleep patterns were once common.

Pre-Industrial Sleep Patterns

Historical scholars have documented references to “first sleep” and “second sleep” in Europe and other regions prior to the Industrial Revolution. People would:

1. Go to bed shortly after dusk,

2. Wake for an hour or more in the middle of the night,

3. Return to sleep until sunrise.

This pattern wasn’t seen as strange; it was simply routine.

Why It Changed

The shift away from segmented or biphasic sleep likely occurred because of:

• Artificial light: Electricity extended the day into the night.

• Industrial work schedules: Regular work hours discouraged waking in the middle of the night.

While not all anthropologists agree that it was universal, these historical records suggest that multiple daily sleep intervals were once common or at least widely accepted in some societies.

Why People Try Biphasic Sleep Today

Interest in biphasic sleep has grown for several reasons:

• Cultural tradition: In some countries, siesta or midday napping is common.

• Work or lifestyle needs: People with irregular schedules or long hours may split sleep to fit their routines.

• Personal preference: Some feel more alert or productive with a nap.

Sometimes people experiment with biphasic sleep to increase waking hours or reduce perceived sleep debt.

What the Research Say

There is evidence suggesting that humans can naturally adopt biphasic sleep in certain environments:

• A 1992 study showed that people living under extended dark conditions shifted to biphasic sleep, with two roughly equal sleep bouts separated by a wakeful period.

• Recent theoretical research argues that biphasic sleep may represent a flexible alternative to traditional monophasic sleep, especially for shift workers or those with disrupted schedules.

However, formal scientific literature on the health impacts of biphasic sleep is relatively limited compared to research on sleep deprivation and circadian rhythms.

What Research Does Say About Sleep & Health

Health authorities like the CDC recommend that adults get at least 7 hours of sleep per night (or within 24 hours) to support physical and mental health. Dispersing sleep across two segments can meet this total if structured properly.

Sleep deprivation — failing to meet these recommendations — is linked to:

• Impaired immune function, cognition, and mood,

• Increased risk of chronic conditions like heart disease and diabetes,

• Weight gain and metabolic disruption.

So whether time is in one block or two doesn’t matter as much as sleep quality and total duration.

Pros and Potential Benefits of Biphasic Sleep

While research is not conclusive, some potential benefits have been suggested:

Why Some People Prefer Biphasic Sleep

1. Increased Alertness and Productivity

• A short nap can increase alertness and reduce daytime sleepiness.

2. Cultural and Environmental Fit

• In regions with hot midday temperatures, a longer midday nap can make daily rhythms more comfortable.

3. Flexible Sleep for Shift Workers

• Biphasic schedules may help people align their sleep with non-traditional work hours, though research in this area is still emerging.

4. Personal Preference & Natural Patterns

• Some people naturally wake during the night; biphasic schedules simply structure sleep around this pattern.

It’s important to note that these potential benefits are based on small studies, anecdotal reports, or hypotheses, not definitive clinical trials.

Risks and Challenges of Biphasic Sleep

Biphasic sleep isn’t ideal for everyone. If done poorly, it can cause:

Potential Downsides

• Sleep fragmentation: Interrupting sleep can reduce overall sleep quality if total sleep time is insufficient.

• Sleep inertia: Longer naps (over ~30 minutes) can leave you feeling groggy.

• Social and work conflicts: Daily rhythms may not fit typical work or school schedules.

• Not effective for everyone: People with insomnia or circadian rhythm disorders may find biphasic schedules worsen sleep.

Importantly, while some experimental and traditional sleep schedules involve multiple sleep bouts, fragmented sleep schedules with very limited total sleep (as seen in extreme polyphasic routines) are associated with adverse effects such as cognitive decline and health issues.

Biphasic Sleep Patterns at a Glance

Here’s how typical biphasic schedules might look in practice:

Biphasic Sleep Around the World

Biphasic sleep is part of cultural tradition in many regions:

• Mediterranean countries: Siestas are customary, often to avoid midday heat and recharge energy.

• Tropical climates: Daily naps align with rest periods when work is difficult or unsafe.

Even in cultures without formal siestas, short daytime naps improve alertness and are common across age groups.

Practical Tips for Trying Biphasic Sleep

If you’re considering experimenting with biphasic sleep, here are some evidence-informed strategies:

1. Establish consistency.

• Go to bed and nap at the same times each day.

• Consistent patterns help your body anticipate rest.

2. Prioritize total sleep.

• Aim for 7+ hours total over the two blocks.

• Avoid reducing sleep time too drastically — it can lead to sleep debt.

3. Use light to your advantage.

• Get bright morning light to support your circadian rhythm.

• Dim lights in the evening to encourage melatonin production.

4. Avoid disruptors.

• Minimize caffeine, heavy meals, and electronics before sleep.

5. Ease transitions.

• Short relaxation routines before both sleep segments can help signal your body it’s time to rest.

Key Takeaways

• Biphasic sleep is a sleep pattern involving two distinct periods of sleep in 24 hours, such as night sleep followed by a nap, or segmented night sleep.

• It has historical precedent and may reflect a natural human sleep rhythm before modern lighting and work schedules changed our habits.

• Scientific research supports the feasibility of biphasic sleep in humans, but its health benefits remain unproven.

• Total sleep time and sleep quality are more important for health than the number of sleep segments, according to guidelines emphasizing ~7+ hours of sleep for most adults.

• Biphasic sleep may work well for some individuals, but it’s not a one-size-fits-all solution.