Originally published October 6, 2024 | Updated October 2026

By Vincent RPSGT | Sleep Blogs

Imagine trying to sleep when the sun never sets.

During the Antarctic summer, some regions experience continuous daylight for weeks or months. Although this creates extraordinary conditions for scientific exploration, it can also interfere with the body’s natural sleep-wake cycle.

Researchers studying Antarctic expedition workers discovered that prolonged daylight was associated with changes in sleep stages, delayed melatonin rhythms, and reduced daytime alertness.

Interestingly, the workers’ shared daily schedules may have helped preserve the normal timing of another important hormone: cortisol.

These findings offer useful insights into how light exposure, biological rhythms, and daily routines influence sleep.

What Happens to Sleep During the Antarctic Summer?

In a study published in the Journal of Applied Physiology in 2017, Belgian researchers investigated sleep and circadian rhythms during a four-month Antarctic summer expedition.

The study involved 21 healthy male expedition members who were exposed to continuous daylight.

Researchers used portable polysomnography equipment to monitor sleep and collected saliva samples to examine melatonin and cortisol patterns.

They also assessed sleepiness, mood, subjective sleep quality, and alertness.

Although 21 participants underwent monitoring, technical difficulties meant that complete sleep-stage data suitable for analysis were available for only nine participants.

This limitation is important when interpreting the findings.

Researchers Discovered Changes in Deep Sleep and REM Sleep

Under typical conditions, deep sleep is concentrated more heavily during the first part of the night, while REM sleep becomes more prominent later.

The Antarctic researchers observed a different pattern.

Among participants with usable sleep-stage recordings:

• Deep sleep, also called slow-wave sleep, was substantially reduced.
• REM sleep increased.
• Deep sleep tended to occur later in the sleep period.
• REM sleep appeared earlier than expected.
• Sleep was more fragmented, with reduced sleep efficiency.

These findings suggested that the normal organization of sleep had been disrupted.

The researchers described this phenomenon as part of what has sometimes been called polar insomnia.

Why Was Melatonin Delayed?

Melatonin is a hormone involved in signaling biological night.

Its secretion is influenced strongly by environmental light and darkness.

Under ordinary conditions, melatonin levels generally rise during the evening and decline toward morning.

During the Antarctic expedition, researchers observed evidence of a substantial delay in melatonin timing.

Some participants still had elevated melatonin levels in the morning, when they were expected to be awake and alert.

This may help explain why expedition members experienced morning sleepiness despite following regular sleeping schedules.

However, because hormone measurements did not cover a complete 24-hour cycle, the investigators could not determine the exact timing of melatonin onset and peak secretion.

What Happened to Cortisol?

Cortisol is often described as a stress hormone, but it also plays an important role in normal daily biological rhythms.

In healthy individuals, cortisol typically rises toward the morning and follows a predictable daily pattern.

Surprisingly, the researchers found that the expedition members maintained a relatively normal cortisol rhythm despite the continuous daylight.

Why might this have happened?

The workers followed a common daily schedule, including shared waking times, meals, and work routines.

The investigators suggested that these social and behavioral routines may have helped maintain the timing of cortisol secretion.

This was a possible explanation, not proof that synchronized schedules caused the preserved cortisol rhythm.

The findings illustrate how environmental light and daily routines may influence different biological systems in different ways.

Why Is This Research Important Outside Antarctica?

Most people will never experience an Antarctic summer, but many face conditions that can interfere with their biological clocks.

Examples include:

• Night-shift workers who sleep during daylight hours.
• Employees working rotating or irregular schedules.
• Travelers crossing multiple time zones.
• People living in regions with extremely long summer days.
• Individuals with delayed sleep-wake schedules.
• People exposed to bright artificial light late at night.

The Antarctic study provides an unusual example of how environmental light and daily schedules may affect sleep.

However, its findings cannot automatically be applied to every shift worker or person with insomnia.

Understanding Your Internal Body Clock

The human body has an internal timing system, commonly called the circadian clock.

It helps regulate:

• Sleep and wakefulness.
• Melatonin secretion.
• Body temperature.
• Alertness and performance.
• Hormonal activity.
• Other daily physiological processes.

Light is one of the strongest signals influencing this clock.

When light exposure occurs at unusual times, the body’s internal rhythms may become misaligned with the person’s required sleep schedule.

This can contribute to difficulty sleeping, excessive sleepiness, and reduced daytime functioning.

Practical Sleep Tips for People Working Irregular Hours

Although the Antarctic research was observational, broader sleep-medicine guidance supports several practical approaches for managing irregular schedules.

1. Protect a Regular Sleep Period

When possible, maintain a consistent sleep schedule, especially if you work permanent night shifts.

People working rotating shifts may need individualized strategies because complete circadian adaptation is often difficult.

2. Create a Dark Sleeping Environment

Use blackout curtains or an eye mask when sleeping during daylight hours.

Reduce unwanted noise and interruptions.

3. Pay Attention to Light Exposure

Light exposure can affect alertness and circadian timing.

For night-shift workers, appropriately timed light exposure and light avoidance may be useful, but the best timing depends on the individual’s schedule.

4. Limit Caffeine Near Bedtime

Caffeine may improve temporary alertness, but consuming it too close to your planned sleep period can make falling asleep more difficult.

5. Allow Enough Time for Sleep

Adults generally need at least seven hours of sleep per night, although individual needs vary.

6. Seek Evaluation for Persistent Problems

If you experience ongoing insomnia, excessive sleepiness, or difficulty functioning because of your work schedule, discuss your symptoms with a qualified healthcare professional.

Melatonin supplements and specialized light therapy should be considered with professional guidance because timing, dosage, and individual circumstances matter.

Can Shift Work Cause a Sleep Disorder?

Some people who regularly work at night or during rotating shifts develop persistent insomnia, excessive sleepiness, or both.

When these problems are associated with a work schedule that overlaps with the body’s usual sleep period, a clinician may consider shift work disorder, a type of circadian rhythm sleep-wake disorder.

Not everyone who works at night develops this condition.

Evaluation may include a medical history, sleep diary, work-schedule review, and assessment for other sleep disorders.

A sleep study is not routinely necessary to diagnose shift work disorder itself, but testing may be recommended when another condition, such as obstructive sleep apnea, is suspected.

What the Antarctic Study Teaches Us

The researchers found that continuous daylight was associated with disrupted sleep architecture and delayed melatonin rhythms.

At the same time, the expedition workers maintained a relatively normal cortisol rhythm, possibly influenced by their synchronized daily schedules.

The study demonstrates that sleep regulation involves more than simply going to bed at a particular time.

Environmental light, internal biological rhythms, and daily behavioral routines interact in complex ways.

Because the study was small and observational, additional research is necessary to determine precisely how these factors influence sleep and hormonal regulation.

When Should You Consider a Sleep Evaluation?

Consider discussing your sleep concerns with a healthcare professional if you experience:

• Persistent difficulty falling asleep or staying asleep.
• Excessive sleepiness during work or while driving.
• Loud snoring or witnessed breathing pauses.
• Unrefreshing sleep despite adequate time in bed.
• Sleep difficulties related to night shifts or rotating schedules.
• Ongoing problems with concentration, memory, or daytime functioning.

Sleep symptoms may have several possible causes, and appropriate evaluation can help identify the next step.

Better Sleep. Better Health.

Understanding the relationship between light, sleep schedules, and the body’s internal clock is an important part of protecting sleep health.

If you have concerns about sleep apnea, excessive daytime sleepiness, or other sleep-related problems, appropriate evaluation may help determine whether diagnostic sleep testing is needed.

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Medical disclaimer: This article provides general educational information and does not replace professional medical advice, diagnosis, or treatment.

Research References

1. Pattyn N, Mairesse O, Cortoos A, Marcoen N, Neyt X, Meeusen R. (2017). Sleep during an Antarctic summer expedition: new light on “polar insomnia.” Journal of Applied Physiology, 122(4), 788–794. https://doi.org/10.1152/japplphysiol.00606.2016
2. American Academy of Sleep Medicine. (2025). Management of Shift Work Disorder: Clinical Practice Guideline.
3. American Academy of Sleep Medicine. Circadian Adaptation to Shift Work — Provider Fact Sheet.