Sleeping Through the Seasons: How Shifting Daylight Affects Our Sleep – As the seasons turn and the days grow longer, many of us welcome the return of warmth, light, and the promise of renewal.
Spring, in particular, signals a shift in mood and energy. The clocks spring forward, sunsets stretch into the evening, and we tend to feel more active and social. Yet, hidden within these cheerful seasonal changes is a quiet disruption: we may begin sleeping less, and not always by choice.
While we often credit poor sleep to busy schedules or screen time, growing research suggests that natural seasonal changes play a much larger role in how long and how well we sleep. Even in today’s artificially lit environments, our biology remains surprisingly connected to the natural rhythms of the Earth.
The Impact of Seasonal Light on Sleep
Each year, as daylight saving time begins and the sun lingers longer in the sky, we subtly adjust our behaviors. We stay outside later, delay bedtime routines, and push our bodies to match the pace of the changing world around us. However, sleep researchers are beginning to question whether these seasonal habits might be at odds with what our bodies actually need.
A recent study reveals that human sleep remains seasonally influenced—even in highly urban environments where artificial light dominates. Researchers tracked the sleep patterns of 188 patients dealing with various sleep disturbances. What they found was both intuitive and surprising: people sleep longer during the darker winter months and get less sleep as summer approaches.
On average, people slept an hour more in December than in June, with the most notable differences seen in REM (rapid eye movement) sleep, the dream-heavy stage linked to emotional processing, memory, and brain health. In winter, people logged about 30 minutes more REM sleep than they did during the summer months that were involved in the research.
REM Sleep and the Circadian Clock
REM sleep is regulated by our circadian rhythm—the internal biological clock that runs on a roughly 24-hour cycle and is influenced heavily by exposure to light. As daylight increases during spring and summer, this clock shifts, nudging us to wake up earlier and stay up later. But unlike a light switch, our bodies don’t adjust instantly or evenly.
REM sleep seems to track with seasonal light exposure. Even when people are surrounded by artificial light, their bodies still respond to the natural increase or decrease in daylight across the year.
Findings underscore just how deeply our sleep is linked to environmental cues. Despite our modern habits—staying up with screens, working under bright fluorescent lights, and sleeping behind blackout curtains—our sleep architecture continues to reflect patterns shaped by millennia of evolution.
A New Discovery: Changes in Deep Sleep
While seasonal changes in REM sleep make sense due to its connection to the circadian rhythm, the Berlin study uncovered something far less expected: seasonal variation in deep sleep, or slow wave sleep (SWS).
Slow-wave sleep is the most restorative sleep stage. During this phase, the body repairs tissues, builds muscle, and consolidates memories. It’s also when the immune system gets a boost and energy stores are replenished. SWS isn’t typically influenced by light but instead is governed by sleep pressure—how long we’ve been awake and how much rest the body needs.
Still, studies show that people experienced 30 minutes less deep sleep in September compared to February, a puzzling discovery that has researchers rethinking what they know about the influence of seasons on sleep.
This Matters: Seasonal Sleep Adjustments
Although the participants in the Berlin study were people already suffering from sleep disorders, the implications may extend to the general population. If seasonal shifts affect sleep even in people living in cities, exposed primarily to artificial lighting, it’s likely that many of us experience similar trends, whether we’re aware of them or not.
This brings up important questions: Should we adjust our sleep routines throughout the year? Would earlier bedtimes in winter and slightly later ones in summer better support our natural rhythms? Considering the studies at hand, it is worth considering, especially for children and adolescents, whose developing brains and bodies are particularly sensitive to sleep changes.
Tips to Stay in Sync with the Seasons
There are practical steps anyone can take to improve sleep across the seasons. Here are a few ways to support your body’s changing needs:
- Maximize natural light during the day, especially in the morning, to help regulate your circadian clock.
- Limit screen exposure at night, as blue light can suppress melatonin production and delay sleep onset.
- Maintain a consistent sleep schedule, even when the days grow longer and social invitations increase.
- Listen to your body—if you feel more tired in the winter, allow yourself extra sleep when possible.
- Use warmer, dimmer lighting in the evening to signal to your brain that bedtime is approaching.
Embracing a Seasonal Sleep Mindset
In modern life, we often overlook nature’s rhythms in favor of efficiency and convenience. We expect our bodies to function the same year-round, regardless of daylight hours, temperature, or environmental shifts. But as the Berlin research suggests, our biology remembers what we’ve forgotten: that humans are seasonal beings.
By recognizing and respecting these natural changes, we can begin to craft sleep habits that not only suit our lifestyles but also align more closely with the needs of our bodies. So as you move through the year—from the long nights of winter to the bright evenings of summer—remember that your sleep, too, is part of the cycle.
You’re not just sleeping through the night. You’re sleeping through the seasons.
If you or anyone you know suffers from a sleeping disorder or has difficulty with their sleep, go to your local sleep doctor or reach out to soundsleepconsultants.com
“Sleep is one of the main roles in longevity.” – Dr. Tawnie Lowther
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