As I dig deeper into the subject of how nature benefits human performance and well being, I am constantly amazed at how much evidence is available. I feel like I’ll never be able to learn even a fraction of what we know—and that doesn’t even account for all the things we do not yet know.
This post is by request: one of my best friends said that she wanted to know how getting outdoors influences sleep. For example, do people sleep better at night if they take a walk outside during the day rather than walk on a treadmill indoors?
This question never occurred to me, as sleeping is one of my greatest skills. I go to bed early so that I can get 8-9 hours of sleep every night. And I nap on weekends, a luxury of not having kids that my dear friend does not have.
So a research topic was born: Do we sleep better if we spend time outside?
Yes, we do. There may be multiple reasons for this, but the clearest connection appears to be between natural light levels and our circadian clock. You have likely heard of circadian rhythms before: these are biological processes within our bodies that occur on a roughly 24-hour schedule and affect eating, sleeping, hormones, and the functions of our organs.
[Sidenote: it’s not just humans that have circadian rhythms. Animals, insects, plants, and even bacteria have been observed as having circadian rhythms. We’re all creatures that have evolved on this planet together over millions of years, so it makes sense that all life is attuned to the sun. However, research on the circadian rhythms of goldfish will have to wait until another day.]
How Light Influences Sleep
A group of nerve cells in the brain called the suprachiasmatic nucleus, or SCN, is the source of our body’s master clock that controls our circadian rhythms and all other biological cycles. The SCN contains about 20,000 nerve cells and is located in the hypothalamus, an area of the brain just above where the optic nerves from the eyes cross. Our circadian rhythm will maintain a roughly 24-hour cycle throughout our lives. It runs on it’s own, but it is influenced by external cues like food or exercise, but light is the most important. Special light-sensitive nerve cells in our eyes transmit information about light conditions to the master clock, which helps keep the clock set to the right time.
If you travel far away, it’s the discrepancy between the body’s master clock and the light conditions that cause jet lag, or even the body confusion of changing on or off of Daylight Saving Time; it takes the body a little while to reset its internal clock.
Several hormones respond to this master clock. Melatonin is most closely tied to sleep. During the day, the light signals coming into your eyes suppress the body’s production of melatonin. Then, when conditions become dark, your body releases melatonin and you become sleepy. Melatonin levels stay high through the night to help the body sleep and restore itself. In the morning, melatonin levels drop and cortisol levels rise, signaling the body to wake. If your circadian rhythm gets out of whack, the risk of chronic diseases like insomnia, high blood pressure, diabetes, and depression rise.
Light, and especially natural light, is absolutely critical to keep your circadian rhythm in check. While most people are generally awake during the daylight hours and asleep during the night, there are a few ways that our predominantly-indoor lifestyles can mess with our clocks.
First, the light outside during the day is typically much brighter than it is inside in our homes and office buildings. This means that while you may be in a lit area during the day, it may not be bright enough to have the same signaling effect as being outside. But even windows and brightly lit spaces can help; for example, one study of university office workers found that those working in offices with windows slept longer, had better sleep, and engaged in more physical activity than their co-workers in windowless offices.
Additionally, the photoreceptors in your eye are most sensitive to light in the blue portion of the spectrum, which is common in natural light. The problem that this creates is that we typically light our homes with bright, blue lights well after the sun goes down—especially during the winter—and this indoor lights hijacks the signal and tells our brain that it’s still daytime. LED lights are particularly bad at messing with our brain cells, as they tend to be rich in the blue wavelengths that communicate with our brains. If you’ve ever been up late watching TV or working on the computer to suddenly realize that it’s way past your bedtime and you aren’t as tired as you should be, you’ve experienced this effect.
And, to make things worse, when we expose ourselves to too much light in the evening, we shift our clocks later, making it a lot harder to wake up in the morning.
How Nature Can Improve Sleep
Both natural and artifical light can affect our circadian rhythms, influencing our sleep and numerous other processes throughout our bodies. To answer my friend’s question, it is possible to use nature to our advantage to improve our sleep.
One part of the equation is to reduce exposure to artificial lights in the evening. This especially means avoiding bright overhead lights and LED screens for a few hours before bed time. There are some products and apps designed to reduce the sleep-disrupting effects of the blue wavelengths in artificial light, but the jury is still out on these. If you’re serious about sleep, avoid late night TV and computer sessions. But that doesn’t mean you have to sit in the dark—using fewer lights of warmer colors can help signal to your body that it’s time to wind down. And, if you’re anything like me, reading a (real, non-electronic) book beneath a single lamp bulb is a surefire pathway to near-instant sleep.
The other part of the equation is to do the opposite of limiting late-night light: try to increase natural light exposure to reset the circadian clock. Artificial light can be used for this purpose, and this can be a good solution for coping with the short winter days found at high latitudes. However, natural daylight is substantially brighter than indoor light, making it the preferable option. Use natural daylight to your advantage to help wake up in the morning or during the day if you’re feeling your energy sag by going out for a stroll or even sitting by a large window.
So go get outside and go get some sleep!
Also, it was really fun to research this topic, which became a Toastmasters speech and then this post. If you have questions about how nature affects our lives and our health, I’d love to hear them!