Sleep cycles

What happens to our brain and body as we sleep?

That’s what we’re exploring this week.

Today’s study investigates the natural sleep cycles that occur during night.

Last week, we explored the 24-hour circadian rhythm. This week, we’re zooming in even further to look at the cycles that make up those 24 hours.

During sleep, we pass through different stages - many people have likely heard of REM and non-REM sleep.

We pass through these stages in cycles known as ultradian rhythms.

So, let’s take a closer look at how these cycles that make up our sleep actually work

Today’s insights is mainly drawn from the scientific article: 

“Ultradian sleep cycles: Frequency, duration, and associations with individual en environmental factors - A retrospective study”

Today's newsletter

• Takeaways:

• The study in a nutshell:

• What they did:

• What the authors found out:

• What can we learn from this study?

Takeaways:

📉 Sleep deprivation alters your sleep patterns

If you are in a sleep deprived state, your body naturally prioritizes deep NREM sleep in the first part of the night and can down regulate the amount for REM sleep you are getting.

😴 You sleep in cycles that do not easily change

Sleep occurs in cycles made up of different stages, including NREM and REM. These cycles are regulated by your internal biology, more than environmental factors.

💡 Light and noise has limited effect  

Contrary to what one may be led to believe, traffic noise and pre-sleep light (up to 250 lux) had no effect on these sleep cycles.

The study in a nutshell:

Today’s study, is a comprehensive retrospective study, meaning that researchers analyzed over 6,000 sleep cycles recorded from 369 healthy participants over a period of 26 years.

Their goal was to understand how ultradian sleep patterns vary depending on age, sex, sleep pressure (how tired someone is), and exposure to light and noise.

The authors found, that while ultradian rhythms are actually really stable and biologically driven, they do show variation with age and sleep pressure.

Older adults tend to experience longer NREM and shorter REM episodes, and women show slightly longer NREM durations than men.

Interestingly, environmental factors like moderate light exposure and nighttime traffic noise had no significant effect on these cycles.

I believe we can use this work to get a better understanding of what actually happens during our nightly sleep, as an important foundation for optimal management and optimization.

Quick question to test your knowledge:

What they did:

What the authors found out:

General Sleep Cycle Patterns

Across more than 6,000 recorded sleep cycles, the average duration of a full NREM–REM cycle was about 99.5 minutes, with a median of 96 minutes.

Most participants experienced three to four complete cycles during an 8-hour night.

Individual Differences: Age and Sex

Age and sex had measurable effects on sleep cycle composition:

• Older adults had longer NREM episodes but shorter REM episodes, especially later in the night. This suggests that aging shifts the balance toward more restorative deep sleep at the expense of dreaming stages.

• Females experienced slightly longer NREM sleep, particularly during the second cycle. No significant sex differences were found in REM duration.

Environmental Factors: Light and Noise

Surprisingly, moderate exposure to nighttime traffic noise and presleep light (up to 250 lux) had no significant effect on the duration of NREM or REM episodes. This suggests that healthy sleepers may be relatively resilient to these common environmental disturbances.

Sleep Pressure: High vs. Low

Manipulating sleep pressure had a noticeable impact:

• High sleep pressure, induced by 40 hours of wakefulness (sleep deprivation), led to longer NREM episodes in the first sleep cycle.

• Low sleep pressure, induced by a protocol of many naps leading up to the sleep, resulted in longer REM episodes, especially during the early part of the night.

What can we learn from this study?

This study provides strong evidence that ultradian sleep cycles - our natural rhythm between deep sleep and dream sleep - are primarily shaped by internal biological processes, not as much by the external environment.

But, age, sex, and sleep pressure all influence the structure of our sleep cycles.

For instance, older adults tend to experience longer NREM and shorter REM episodes. Women typically have slightly longer NREM sleep than men, and sleep pressure (sleep deprivation) significantly increases the amount of NREM sleep we get.

What I found particularly interesting in this study, however, was that light and noise - often assumed to disrupt sleep - had no measurable effect on these ultradian sleep cycles.

However, that’s not to say these factors do not affect overall sleep quality.

Today’s study did not include subjective measuress of sleep quality or physiological markers. For example, heart rate variability (HRV) is a well-known indicator of the balance between our sympathetic and parasympathetic nervous systems - a useful measure of bodily balance between rest and readiness.

It would have been interesting to see how HRV and subjective sleep quality were influenced by noise and light exposure.

Still, this result raises a question; are noise and light really as harmful to our sleep as we think?

As today’s study shows, our body is naturally good at compensating for sleep deprivation by prioritizing NREM sleep, so might it also be more resilient to environmental factors like noise and light than we assume?

At the very least, these findings might be a gentle reminder that we could stress a bit less about making our environments perfect before sleep.

Properly, our mental state has a bigger impact on our sleep quality than a little noise and light.

This is something we will take a closer look at next week. 

_{Disclaimer: The above is mainly based on the article “Ultradian sleep cycles: Frequency, duration, and associations with individual and environmental factors - A retrospective study” by Christian Cajochen, Carolin Franziska Reichert, Mirjam Münch, Virgine Gabel, Oliver Stefani, Sarah Laxhmi Chellappa & Christina Schmidt and aims to provide key takeaways and a condensed overview of its content. While the essence is drawn from the original article, some parts have been simplified or rephrased to enhance understanding. Please note that we at, OptiMindInsights or any other potential writers or contributors to our summaries, do not accept responsibility for any consequences arising from the use of this summary. The information provided should not be considered a substitute for personal research or professional advice. Readers are encouraged to consult the original article for detailed insights and references. The summary does not include references, but they can typically be found within the original publication. Always exercise due diligence and consider your unique circumstances before applying any information in your personal or professional life. We refer to the creative commons for reproducibility rights.}