Seasonal Changes and Sleep: How Sunlight and Temperature Affect Your Sleep Cycle
With September in full swing, seasonal changes are right around the corner. As summer transitions into fall, you may notice subtle changes in your sleep—even before the end of Daylight Saving Time. Earlier sunsets, changing temperatures, and shifts in daily sunlight exposure can all influence your circadian rhythm, the internal biological clock that helps regulate your sleep-wake cycle.
So, if you feel like your sleep habits change with the seasons, you're probably not imagining it. Research suggests that seasonal changes in light exposure and temperature can have a meaningful impact on when we feel sleepy, when we wake, and how much sleep we get.
Light, Temperature, and Your Circadian Rhythm
Light is one of the most powerful environmental cues for regulating the circadian rhythm. Our internal 24-hour clock uses changes in light and darkness to stay synchronized with the natural day-night cycle. As the seasons change, so does the amount and timing of natural light we receive, which can influence the timing of our sleep.
Interestingly, our sensitivity to light can also vary depending on our previous exposure. Research has found that exposure to dim light or darkness can increase the effects of nighttime light on melatonin suppression and circadian timing compared with exposure to brighter light.
While light is a primary signal for the sleep-wake cycle, temperature also plays an important role. Our bodies naturally experience changes in temperature throughout the day, and research suggests that sleep onset is often associated with periods when ambient temperatures are falling. In natural environments, waking may also be more closely related to the lowest temperature of the daily cycle than to sunrise.
Seasonal changes may therefore influence sleep through a combination of environmental cues, including daylight, temperature, and our daily routines.
How the Seasons Can Change Your Sleep
Research increasingly suggests that sleep patterns naturally shift throughout the year. In one study examining sleep in a rural elderly population in France, researchers found significant seasonal effects on the sleep-wake cycle. Because participants lived relatively stable daily schedules with less exposure to urban noise and artificial light, the researchers were better able to observe the potential influence of the seasons themselves.
Another study followed more than 500 university students in Seattle and found that seasonal changes affected sleep timing even when students were following relatively structured academic schedules. During winter school days, students went to sleep approximately 35 minutes later and woke about 27 minutes later than they did during the summer. When sleep timing was compared with solar midnight, the seasonal difference was approximately one hour.
One of the most interesting findings from this research was the importance of daytime light exposure. Researchers found that daytime light was a stronger predictor of circadian timing than light exposure after dusk. Each additional hour of daytime light exposure was associated with an earlier circadian phase, while evening light had a smaller but opposite effect.
This highlights an important point: when you get light may matter just as much as how much light you get. Getting sufficient natural light during the day can help reinforce the signals that tell your body when it is daytime and when it is time to prepare for sleep.
What About Artificial Light?
Modern life has dramatically changed our relationship with natural light. Instead of following the natural progression from bright daylight to darkness, many of us spend our days indoors under artificial lighting and our evenings surrounded by screens, overhead lights, and other sources of illumination.
This can make it harder for the circadian rhythm to respond to seasonal changes in natural light.
Research examining people living according to natural light-dark cycles found that their biological clocks were able to synchronize more closely with solar time. During a period of natural outdoor exposure, the timing of the biological night shifted to more closely align with sunset and sunrise.
Other research has found that the human circadian system does respond to seasonal changes in natural light, including a longer biological night during winter. However, exposure to modern electrical lighting can reduce this seasonal response and contribute to later circadian timing throughout the year.
The good news is that our environment isn't the only thing influencing our circadian rhythm. Increasing exposure to natural light can help reinforce healthy circadian timing. Even something as simple as spending more time outdoors can provide a powerful environmental signal to your internal clock.
Supporting Healthy Sleep During Seasonal Transitions
We can't change the Earth's axis or control how quickly the days become shorter, but we can support our bodies as the seasons change.
One of the simplest strategies is to prioritize daytime light exposure. As the days get shorter, try stepping outside during the middle of the day for 5–10 minutes of natural light and a quick walk. Whenever possible, spend time outdoors rather than relying exclusively on indoor lighting.
You can also make the most of the changing season by planning outdoor activities such as a fall hike, weekend camping trip, or simply enjoying time outside with friends and family. These activities aren't just enjoyable—they can also give your body more exposure to the natural light-dark cycle.
As fall approaches, consider gradually aligning your daily routines with the changing daylight hours. Consistent wake and sleep times, regular daytime light exposure, and a darker environment in the evening can all help reinforce your body's natural sleep-wake rhythm.
Embrace the Change of Seasons
Seasonal transitions are a natural part of life, and your sleep cycle may naturally shift along with them. Changes in sunlight, temperature, daily routines, and artificial light exposure can all influence your circadian rhythm and the timing of your sleep.
Rather than fighting these changes, consider using the transition into fall as an opportunity to reconnect with natural light, spend more time outdoors, and establish routines that support healthy sleep.
Looking to Support Your Sleep Naturally?
Concerned that seasonal changes, stress, light exposure, or daily habits may be affecting your sleep cycle and overall wellness?
Book a FREE 15-minute meet and greet with Dr. Kellyann Tomko to learn how personalized functional and integrative care may help support healthy sleep, circadian rhythm balance, energy, and your long-term wellness goals.
Author: Dr. Kellyann Tomko, ND
References
Adamsson M, Laike T, Morita T. Annual variation in daily light exposure and circadian change of melatonin and cortisol concentrations at a northern latitude with large seasonal differences in photoperiod length. J Physiol Anthropol. 2016;36(1):6. doi:10.1186/s40101-016-0103-9.
Yetish G, Kaplan H, Gurven M, et al. Natural sleep and its seasonal variations in three pre-industrial societies. Curr Biol. 2015;25(21):2862-2868. doi:10.1016/j.cub.2015.09.046.
Jouvencel A, Altena E, Pérès K, et al. Impact of seasons and temperatures on the sleep-wake cycle in a French elderly rural population. Sleep Med. 2025;131:106510. doi:10.1016/j.sleep.2025.106510.
Dunster GP, Hua I, Grahe A, et al. Daytime light exposure is a strong predictor of seasonal variation in sleep and circadian timing of university students. J Pineal Res. 2023;74(2):e12843. doi:10.1111/jpi.12843.
Stothard ER, McHill AW, Depner CM, et al. Circadian entrainment to the natural light-dark cycle across seasons and the weekend. Curr Biol. 2017;27(4):508-513. doi:10.1016/j.cub.2016.12.041.
Disclaimer:
This information is generalized and intended for educational purposes only. Due to potential individual contraindications, please see your primary care provider before implementing any strategies in these posts.
