Why Am I More Tired in the Fall? How Seasonal Changes Affect Sleep
As the days get shorter and the sun starts setting earlier, you might notice a change in your sleep too.
Maybe you're getting tired earlier in the evening, finding it a little harder to get out of bed, or wanting more sleep than you did during the summer.
If you've wondered, "Why am I more tired in the fall?", there may be a biological reason.
Research suggests that human sleep and circadian rhythms change with seasonal shifts in daylight. This doesn't mean that everyone suddenly needs hours of extra sleep in the winter, but some seasonal variation in sleep timing and duration appears to be normal.
Why shorter days can affect your sleep
Our sleep-wake cycle is regulated partly by our circadian rhythm, the internal biological clock that helps coordinate sleep, wakefulness, hormone secretion and other physiological processes across the day.
If you want to learn more about how your internal body clock works, you can read my guide to circadian rhythm here.
One of the strongest signals regulating this clock is light.
Morning and daytime light help signal wakefulness and regulate the timing of our internal clock. As darkness increases in the evening, melatonin rises and helps signal biological night.
As we move from summer into fall and winter:
Sunset occurs earlier
Nights become longer
Total daylight exposure decreases
Morning light may occur later
We often spend more time indoors
For those of us living in Canada and other northern climates, these seasonal changes in daylight can be substantial.
Modern lighting allows us to turn on the lights at 5 PM and continue our evening much as we would in July. Our circadian biology, however, hasn't completely stopped responding to changes in the natural light-dark cycle.
Do humans actually sleep more in winter?
On average, research suggests that we may sleep a little longer during the darker months.
A large study published in 2025 analyzed approximately 73 million nights of objectively measured sleep from more than 116,000 adults. In northern regions, people slept approximately 20 minutes longer during winter, with seasonal differences becoming smaller closer to the equator.
Research under more natural lighting conditions suggests that the difference can sometimes be greater. A study of three pre-industrial populations in Tanzania, Namibia and Bolivia found a difference of nearly one hour between summer and winter sleep duration.
Interestingly, people didn't simply fall asleep when the sun went down. Sleep began an average of approximately 3.3 hours after sunset.
This is an important distinction. Humans aren't necessarily programmed to go to bed as soon as it gets dark. Instead, our sleep appears to respond to a combination of environmental signals, including light, darkness and temperature.
Artificial light may be changing our natural sleep patterns
For most of human history, nighttime was actually dark.
Today, darkness outside doesn't necessarily mean darkness inside. We have overhead lighting, televisions, smartphones, tablets and laptops extending our exposure to light well beyond sunset.
One fascinating study compared two Indigenous Toba/Qom communities in Argentina with similar cultural backgrounds but different access to electricity. Both communities slept longer during winter than summer. However, access to electric light was associated with later sleep onset and shorter sleep duration.
Later research in the same population found that access to electricity was also associated with a later onset of melatonin secretion during winter, suggesting that evening artificial light can influence not only when we choose to go to bed, but also the timing of our internal circadian clock.
This doesn't mean we need to turn off every light as soon as the sun sets. It does demonstrate that our light environment can influence our sleep biology.
Does our body actually recognize longer winter nights?
Experimental research suggests that it can.
In controlled studies, researchers have exposed healthy adults to substantially longer periods of darkness. Under these conditions, the duration of nighttime melatonin secretion expanded, along with changes in sleep timing and duration.
These were experimental conditions and shouldn't be interpreted to mean that humans need extremely long periods of sleep every winter. Instead, they demonstrate something more fundamental: human circadian physiology remains sensitive to photoperiod, or the length of the light-dark cycle.
Our internal clock isn't necessarily designed to behave identically in July and January.
So, should you go to bed earlier in the fall?
If you're naturally getting sleepy earlier, it may be reasonable to listen to that signal rather than automatically pushing through it.
For example, if you comfortably stayed awake until 10:30 or 11 PM during the summer but now find yourself genuinely sleepy at 9:30 or 10 PM, an earlier bedtime may simply give your body the additional sleep opportunity it is asking for.
That doesn't mean everyone needs a specific amount of extra sleep during fall or winter. We don't have evidence to prescribe an additional 30 minutes or hour of sleep to everyone simply because the season has changed.
Instead, the research suggests that some flexibility in our sleep timing across the year may be normal.
How to support your sleep as the days get shorter
You don't need a complicated sleep routine to support your circadian rhythm through fall and winter.
Get outside in the morning. Outdoor light is generally much brighter than typical indoor lighting, even when it's cloudy. Morning light provides an important timing signal to your circadian system (to stop melatonin production).
Get daylight during the day. When daylight hours are limited, intentionally getting outside can help maintain a strong distinction between daytime and nighttime.
Pay attention to genuine evening sleepiness. If you're consistently tired earlier than you were during the summer, consider allowing your bedtime to shift earlier.
Keep your wake time reasonably consistent. Regular wake times provide another predictable timing cue for your circadian system.
Dim things down before bed. You don't need to live by candlelight after sunset, but reducing unnecessarily bright light as bedtime approaches can help create a clearer transition between day and night.
The goal isn't a "perfect" sleep routine. It's to give your brain clear signals about when it is daytime and when it is nighttime.
When fall fatigue may be more than seasonal
There is an important difference between feeling ready for bed a little earlier and experiencing significant or persistent fatigue.
If you're sleeping much longer than usual, struggling significantly to wake up, falling asleep during the day, or noticing a substantial change in your energy, concentration or mood, it may be worth investigating further.
Persistent fatigue or waking unrefreshed can have many causes, including insufficient or disrupted sleep, obstructive sleep apnea, vitamin/mineral deficiency, hormone/thyroid dysfunction, medication effects and mental health concerns, among others.
In other words, feeling a little sleepier as the days get shorter can be normal. Feeling exhausted all the time shouldn't automatically be blamed on the season.
The takeaway
Your sleep doesn't necessarily have to look exactly the same in October as it does in July.
Humans evolved in environments where light, darkness and temperature changed throughout the year, and modern research suggests that our sleep and circadian systems retain some sensitivity to these seasonal changes.
So if you're naturally wanting to go to bed a little earlier or sleep a little longer as fall arrives, you don't necessarily need to fight it.
At the same time, if you're getting adequate sleep but still waking unrefreshed or struggling with persistent fatigue, it's worth looking more closely at your sleep quality and overall health rather than assuming it's simply the darker weather.
References
Scott H, Lechat B, Sansom K, et al. Variations in sleep duration and timing: weekday and seasonal variations in sleep are common in an analysis of 73 million nights from an objective sleep tracker. Sleep. 2025;48(9):zsaf099. doi:10.1093/sleep/zsaf099.
Yetish G, Kaplan H, Gurven M, et al. Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology. 2015;25(21):2862-2868. doi:10.1016/j.cub.2015.09.046.
de la Iglesia HO, Fernández-Duque E, Golombek DA, et al. Access to electric light is associated with shorter sleep duration in a traditionally hunter-gatherer community. Journal of Biological Rhythms. 2015;30(4):342-350. doi:10.1177/0748730415590702.
Wehr TA. The durations of human melatonin secretion and sleep respond to changes in daylength (photoperiod). Journal of Clinical Endocrinology & Metabolism. 1991;73(6):1276-1280. doi:10.1210/jcem-73-6-1276.
Blume C, Garbazza C, Spitschan M. Effects of light on human circadian rhythms, sleep and mood. Somnologie. 2019;23(3):147-156. doi:10.1007/s11818-019-00215-x
