Could better sleep be as easy as a walk in the park?
For nearly four billion years, life on Earth has revolved around dark nights and bright days (unless you live near one of the poles). This cycle ledto the development of our 24-hour internal clock -- our circadian rhythm -- and a similar cycle is present in nearly every living species.
Before the invention of lightbulbs, we were limited to campfires and candles or oil lamps at sunset, and our ancestors slept pretty well. In fact, while evidence from a study in Cellmagazine concluded that people living in pre-industrial tribes in Bolivia, Tanzania and Namibia don't necessarily sleep longer, they do appear to sleep through the night.
Despite all of our modern conveniences, fancy mattresses, dark shades, and sound machines, Sleep Foundation polling data reveal that 48% of Americans suffer insomnia occasionally, while 22% say they have insomnia every night or almost every night. An inability to sleep is not just annoying. It is dangerous and is linked to health issues such as obesity, diabetes, depression.
While factors like too much caffeine, exposure to blue light in the evening, high anxiety, and eating or exercising too close to bedtime play a role in keeping us awake at night, few people stop to think about the role of regular sunlight exposure.
The Sleep-Sunlight Connection
You might ask: how can scientists test whether sunlight exposure helps regulate sleep? The answer is to study people who are living in an environment where it's dark nearly 100% of the time.
Researchers reviewed 250 scientific studies of individuals living under 24-hour night conditions. They found that, in fact, such conditions result in a disruption to circadian rhythms which led to late sleep timing and lower sleep efficiency. Translation: without the sun it is difficult to get to sleep, and sleep quality is worse.
It’s well known that people in northern Europe, in particular Norway, suffer from what’s called midwinter insomnia — which mostly means difficulty falling asleep that time of year.
Think this doesn’t apply to you? Think again.
How often do you get outside without sunglasses or see the sun when you’re not behind a windshield or window? In winter months you may even get dressed and drive to before sunrise, work indoors and then return home after dark. According to the National Sleep Foundation, humans spend more than 90% of their waking hours indoors -- and indoor lighting does not have the same effect on our circadian rhythm as real sunlight.
In another study, reported in the journal Sleep Health, office workers used a device to collect personal light exposure during both winter and summer and then self-reported measures of mood and sleep. Those who received more early sunlight exposure reported falling asleep faster, having better sleep quality, and experiencing less depression.
Sunlight and Melatonin Production
Melatonin is the hormone that signals to our body that it’s time to sleep in the evening. When we are exposed to sunlight (or very bright artificial light) in the morning, our brains release melatonin earlier in the evening, allowing us to fall asleep more easily. Nathanial Mead writes in Environmental Health Perspectives, that this "melatonin-rhythm phase advancement" has been effective against insomnia, premenstrual syndrome, and seasonal affective disorder.
Melatonin researcher Russel J. Reiter of the University of Texas Health Science Center also notes that the light we get from being outside on a summer day can be a thousand times brighter than we’re ever likely to experience indoors. For this reason, it’s important that people who work indoors get outside periodically. This can have a major impact on melatonin rhythms and can result in improvements in mood, energy, and sleep quality.
How to Use Sunlight to Fall Asleep
Sunlight for better sleep sounds paradoxical, no? But our brains evolved to wake up with the sun, and sunlight is how we continue to set our internal clock.
Here’s what to do:
- Get morning sun! Morning exposure is best without sunglasses, as they can limit the eyes’ access to full sunlight.
- The body is most responsive between 6 a.m. and 8:30 a.m., and ten to fifteen minutes is all you need.
- Try a walk in the morning to get the added benefit of exercise. But if you can’t do that, sit outside. Look around you to maximize the angles at which sunlight hits your retinas.
- If you miss the early morning, don’t give up entirely. Go outside at lunchtime. Some sunlight is better than none.
- After consistent exposure for ten to fourteen days, see if you feel sleepy earlier in the evening. Monitor if your sleep quality improves.
- If it’s simply too cold in the winter to go outside, or you’re in darkness or indoors most of the day, consider a light-therapy box that can replicate the full-spectrum light you would get from the sun.
Here’s what not to do:
- Don’t assume your morning commute counts. Sitting behind a windshield is similar to wearing sunglasses. You will limit your exposure to beneficial rays.
- Don’t assume that sitting by a window counts. Yes, exposure to sunlight through a window can positively affect your mood, but it won’t help with melatonin production.
- Don’t stress if you miss a day or two. The idea is to create a long-term habit.
- Don’t assume there is no sunlight on rainy or cloudy days. Ultraviolet rays from the sun are still plentiful despite your inability to see them.
Sun exposure has gotten a bad reputation over the last century, as we have learned more about the risks associated with tanning and time outside. Ultraviolet light penetrates deep into the skin, causing damage and promoting skin cancer. But it is also true that -- in addition to regulating your sleep -- sunlight exposure is important for bodily processes including:
- Vitamin D production
- Reduction of an overactive immune response
- Endorphin production
The best news is you don’t have to be outdoors for hours to notice improvement: short periods of exposure will earn you the benefits.
There’s no denying evolution: when it comes to sleeping soundly, we simply need to see the sun.