It’s a crisp, fall day in mid-November, and though your calendar is filled with evening get-togethers and morning runs, you’re feeling sluggish. All you really want to do is sleep in, or to curl up on the couch and nap. Are you being lazy, or do you really need more sleep as the temperature lowers and the amount of daylight decreases? The answer isn’t so clear-cut.
“I don’t think we need more sleep as the days get shorter, but people will often feel sleepier,” says Dr. Karin Johnson, a sleep medicine specialist and spokesperson for the American Academy of Sleep Medicine (AASM), a global network of sleep medicine specialists that advances sleep health worldwide.
Reasons we feel more lethargic in winter and fall
Overall, we naturally tend to sleep more in winter and as the weather generally gets colder into fall. Johnson believes that there are a couple of theories as to why. “One is that when the days are shorter our melatonin levels are higher,” she says. Melatonin is a naturally produced hormone that regulates our sleep-wake cycle. But having too much of it can make us drowsy and reduce our energy levels, causing us to want to snooze longer.
“The other is that there’s more disruption to our circadian rhythm,” a body’s natural 24-hour clock which regulates our sleep-wake cycle. As daylight hours diminish, our circadian rhythm shifts. This can throw off our sleep schedules and lead to excess fatigue. “Especially if we’re not getting enough morning light.”
We tend to spend more time indoors in winter as opposed to warmer months, meaning less natural light. This disconnects us from nature’s rhythms and can shift our natural sleep patterns. When mornings are dark it’s more difficult to get out of bed, since morning sunlight helps regulate circadian rhythm and signals our bodies to wake.
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REM Sleep in Winter
Data published in 2023 in the scientific journal Frontiers in Neuroscience shows that people experience longer REM sleep—the fourth and final stage of the sleep cycle which is when most dreaming occurs—in winter than they do in summer. REM sleep is essential to healthy brains, mood regulation, and mental clarity.
While humans don’t “hibernate” like animals do, we do tend to go into a hibernation-like mode when the seasons change: slowing down, eating heartier foods, and feeling more lethargic overall. Our bodies also compensate for less sunlight by providing us with more REM sleep.
The roles of temperature and food in sleep
“In general, people sleep better when it’s cooler,” says Johnson. However, if it’s cold outside and we jack up the heat, then we might become even sleepier. Our bodies also work harder to preserve heat when it’s cold out, which can bring on “winter fatigue” and make us feel groggier.
We tend to eat heavier, more carbohydrate-dense foods (a.k.a. “comfort foods”) in winter, which can lower our overall energy level since these types of meals take longer to digest. With less energy, we’re also prone to less exercise. It’s almost a ricochet effect.
Seasonal Affective Disorder (SAD)
About five percent of adults in the U.S. experience Seasonal Affective Disorder (SAD), symptoms of depression that occur during the winter months. SAD is linked to reduced sunlight, which along with increasing melatonin levels and disrupting our circadian rhythms, also reduces the amount of serotonin—a natural mood enhancer—that our bodies produce. Feeling sleepy is often a common symptom.
Seasonal Affective Disorder (SAD) affects about five percent of adults in the United States.Video: Seasonal Affective Disorder, Mayo Clinic Health System
How to handle winter sluggishness
In short, while our bodies might not have a biological need for more sleep in winter, changes in daylight, diets, temperatures, and moods often make us want to stay in bed longer. Which is OK. The trick, says Johnson, is sticking to a schedule.
“Sleep when it feels natural. Wake when you feel refreshed,” she says. “Just make sure you prioritize time for sleep, which a lot of people don’t do.” Johnson stresses the importance of morning light in keeping up with our daily routines. “If you don’t get that natural light exposure, using a light box for about 30 minutes each morning can be very helpful.”
Since most people’s waking time is usually out of our control due to school or work schedules, Johnson says going to sleep earlier in the winter might help accommodate human seasonality. “Try turning off electronics in the evening, keep a regular eating schedule during the day, and make sure you’re getting good exercise.” It’s about adjusting to the season as much as possible, which simply might mean sleeping more.
And really, what’s so wrong with an extra hour or two of zzzs?
This story is part of Popular Science’s Ask Us Anything series, where we answer your most outlandish, mind-burning questions, from the ordinary to the off-the-wall. Have something you’ve always wanted to know? Ask us.
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