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Lifestyle

Do Seasons Really Affect Your Sleep Cycle?

Tara Youngblood

12.10.19

Do Seasons Really Affect Your Sleep Cycle?

In talking about how seasons can affect your sleep cycle, we can look to a recent study by Jerome Siegel (University of California, Los Angeles) for guidance. He and his team studied three hunter-gatherer societies in rural parts of Africa and South America and came away with three key findings: the groups actually do not sleep more than we do today, clocking in with a range of 5.7–7.1 hours of sleep a night; they go to sleep roughly three hours after sunset and rise before dawn; and “temperature appears to be a major regulator of human sleep duration and timing.”

While there are other factors that influence your sleep cycle, light and temperature are two critical ones, and the changes in seasons obviously impact those two key factors. While modern conveniences have reprogrammed our sleep cycles, there are steps we can take to sleep as soundly as our ancestors did.

The Impact of Light on Sleep

While there have been assumptions that our ancestors went to sleep at nightfall and slept till sunrise, Siegel’s study told a different story. He and his team monitored three preindustrial societies— the Hadza (Tanzania), San (Namibia), and Tsimane (Bolivia)—and found that as darkness fell and their Sleep Drive was activated, these tribes began prepping food, eating dinner, and planning for the next day, going to bed roughly three hours after sunset. Then they rose before daybreak, which allowed them to get peak light exposure around 9:00 am each day. The hunter-gatherers then retreated to the shade during the hottest parts of the day.

A key aspect of the hunter-gatherers’ daily routine is that sun exposure. Light is an important part of your circadian rhythm—it can be a signal of when to sleep and when to wake up—but it’s one that changes subtly throughout the year. For instance, our days get shorter during the fall and winter, so we typically get less sunlight. In modern times, this is all compounded by the fact that many of us work indoors throughout the day. But why is getting sunlight so important? Because it’s our main source of Vitamin D, which is critical for maintaining serotonin levels.

Serotonin is a key contributor to your sleep-wake cycle, so getting enough sunlight on a daily basis should be a priority. Per this Amerisleep.com article:

“If you work indoors, make it a point to get several minutes in the sun on a break or in the morning when possible. According to Purdue University research, people with fair skin need nine minutes, medium skin 16 minutes, and dark skin 38 minutes to absorb 2000 IU of vitamin D with 25% of skin exposed.

If you can’t get outside regularly, then work near a window. In one study, office workers who sat near windows received higher white light exposure and also slept better than those who didn’t have windows nearby.”

Additionally, you can take a Vitamin D supplement if you’re concerned that you’re not getting enough sunlight. This also answers the question about whether or not seasons affect your sleep cycle. In the case of light, it definitely can, especially if you’re living in parts of the world that get even less than others.

The Impact of Temperature on Sleep

Temperature, however, is not as greatly affected by the seasons. That’s the irony of modern life: while we now have more control over our sleep environments than ever before, with comfortable beds, sun-blocking curtains, and other conveniences, the static nature of our homes can contribute to sleep issues.

To discuss temperature and its effect on sleep, all you have to do is check out some of our previous posts. But today we’ll frame it through Siegel’s study again, and a 2015 theatlantic.com article that discussed his findings:

“The Hadza, Tsimane, and San were also strongly affected by falling temperature, much more so than failing light. They start to sleep as the night cools and begin waking up at its coldest point. ‘This suggests that temperature is a very strong and evolutionarily old signal that gets integrated into sleep-regulating systems in the brain and that we could exploit better,’ says Eus van Someren (Netherlands Institute for Neuroscience). And as Siegel adds, ‘This temperature rhythm has been reduced or completely eliminated for most of us by our shelters and heating systems.’”

In other words, the fact that we have thermostats means we’re not subjected to the whims of the seasons—or the benefits of dropping temperatures. It could be the dead of winter and you could still wake up hot and sweaty in bed, which we know is not conducive for a good night’s sleep—especially as it relates to deep sleep. 

The good news about van Someren’s comment on “exploiting” the sleep-regulating systems in the brain is that this is more possible now than ever before; our chiliPAD and OOLER sleep systems are designed expressly to control your core body temperature during the night, ensuring that it drops to your ideal sleeping temperature to promote deep sleep. While the “best” temperature for sleep is different from person to person, the fact that we have that capability now—along with the thermostat—means that the temperature fluctuations that come with the seasons shouldn’t impact your sleep cycle nearly as much as changes in light would.

It All Comes Back to Healthy Sleep Habits

Optimizing your sleep is not a seasonal quest. We often tout the power of healthy sleep habits, and it’s no different here. Maintaining a consistent sleep schedule will certainly help if you’re a person whose sleep is deeply affected by the changing of the seasons. In fact, this was the third key finding of Siegel’s study: their hunter-gatherer subjects woke up at the same time every day.

The article on theatlantic.com notes that though the Hadza, Tsimane, and San are not “ancestral humans,” their disparate locations combined with their sleep pattern similarities give us an idea of our basic wiring. And, armed with the knowledge they provided, we have the potential to sleep soundly, no matter the season, especially when you consider that we can keep our beds cool enough to enhance our sleep, yet still roll out from under the sheets into our comfortable 70-degree homes. 

Do you have tips for sleeping well throughout the year? If so, we’d love to hear them.