Below, Rowan Jacobsen shares five key insights from his new book, In Defense of Sunlight: The Surprising Science of Sun Exposure.
Rowan is an award-winning science writer, and for the past nine years he has been diving into research on light and how it affects the body. He has written for Harper’s, Outside, The Atlantic, Scientific American, Smithsonian, The New York Times, The Washington Post, MIT Technology Review, Businessweek, and others, and his work has been anthologized in The Best American Science & Nature Writing.
What’s the Big Idea?
Humans evolved to thrive under the full spectrum of sunlight, not the artificial lightscapes that dominate our days. Regular, safe exposure to natural light supports everything from cardiovascular health and metabolism to mood, cognition, and longevity.
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1. Light leads to long life.
A few decades ago, several studies around the world started tracking the amount of sunlight that people were exposed to. The goal was to prove that sun exposure raised the risk of skin cancer. In the old days, they did this through questionnaires and latitude, because the farther you are from the equator, the less light you get on average. Today, they use NASA satellite data or attach light-sensing watches to volunteers’ wrists. The evidence consistently showed that sun exposure does raise the risk of skin cancer.
That wasn’t a surprise. What was surprising was what else it showed: People who got a lot of sun exposure were much healthier than those who didn’t, and they were less likely to die. The biggest difference was in cardiovascular disease, including heart attacks and strokes, which were less common among the sun-getters. They also had lower rates of many cancers and autoimmune diseases, as well as diabetes and dementia. Because those diseases combined kill hundreds of times more people than skin cancer, which is rarely fatal, the overall health and longevity of the sun-getters was much higher. It’s now well established that sunlight corresponds to good health. The question, of course, is why.
2. Light is physical.
The secret to understanding the benefits of sunlight is to change how you think about light. To most of us, it’s not quite physical. Matter is real, but light is just background, the stage setting against which the drama of existence unfolds. But any quantum physicist would tell you that nothing could be further from the truth. Light is as real as any atom. It’s pure energy, pouring out of the sun in tiny packets called photons that find their way to Earth eight minutes later.
Once light gets here, it has a huge effect on the atoms it meets, especially the ones in your body. When a molecule absorbs a photon of light, it becomes energized and starts behaving differently. It can bond with other atoms to form new molecules, break apart, or vibrate like a bell, sending a signal to the rest of the body.
“Once light gets here, it has a huge effect on the atoms it meets, especially the ones in your body.”
The effect depends on how much energy the photon carries. Photons come in a wide range of energy levels and wavelengths, and we detect those differences as colors. Ultraviolet light has the most energy, blue and green are in the middle, and red and infrared photons have the least energy. The important thing to remember is that they are all contained in sunlight, which you can think of as a kind of multivitamin.
Because of these differences in energy, each color of light affects different molecules in the body. Ultraviolet light can damage DNA, but it also makes vitamin D, an essential hormone, and nitric oxide, which lowers blood pressure. Blue light increases alertness and cognition. Green light soothes us. Infrared light scatters through the entire body, improving metabolism and accelerating healing. The body depends on the full spectrum of light to achieve its daily tasks and to keep track of where it is in the day/night cycle. Without that dose, it can lose its way.
3. We are designed for sunlight.
A big reason for poor health in industrial societies is because our diets have changed radically from what we are meant to eat. When humans evolved in Africa, there were no ultra-processed snacks or fast food. We can get by for a short time on such unhealthy fare, but our well-being ultimately depends on sticking with the whole foods we ate in pre-industrial times.
The same is true of light. Although we rarely think about it, our modern lightscape bears even less resemblance to ancient norms than our modern diet. We spend, on average, about 23 hours per day indoors, bathed in artificial light. The photons emanating from LED bulbs and screens are unlike anything we ever experienced in the ancient past. The brightness is only about one percent of the brightness of sunlight, and large portions of the solar spectrum are missing entirely. It’s essentially junk light.
The result is that we spend almost all our time in light that our bodies and minds don’t recognize as daylight, and we never truly wake up. We just wander through our days like zombies, in what the chronobiology experts call “biological darkness.” The negative impact on our health can be severe. But the solution is very simple: Get sun. Not too much. Go outside.
4. Everybody’s different.
How much sunlight should you get? There is no simple answer. We’re all different. Everybody has unique needs, depending on who they are, where they are, and what time of year it is.
The most important factor is skin tone. People with very fair skin, who easily burn and never tan, are much more susceptible to skin cancer, and they need to be very cautious about sun exposure. They’re the ones the recommendations are written for. But people with very dark skin have virtually no risk of sun-induced skin cancer. For them, a daily dose of sunlight is just what the doctor ordered. People with intermediate skin tones can benefit greatly from small amounts of sunlight, while taking care never to burn.
“The most important factor is skin tone.”
In addition, where you live greatly affects your sun diet. People in Australia tend to get too much, while people in Minnesota struggle to get enough much of the year. Other factors like diet and exercise also influence sun tolerance. Most people have a pretty good sense when they’ve had too much. The trick is to err on the side of safety and to never lie out on the beach all day. You are not a lizard.
5. You are energy.
The more I began to think about the way the energy from light cascades through the body, the more I began to think of us as tai chi masters, channeling that energy into our molecules and bending it into patterns that flow through the body and maintain good health. Then, I suddenly realized that I had the metaphor all wrong. We’re not the tai chi masters. We’re the energy!
The essence of a river is not the rocks and dirt of the riverbed. It’s not even the individual drops of water, which are constantly changing. It’s the standing wave, the flow. And you, too, are the standing wave of energy flowing through the substrate of your cells. Every action that makes you alive, whether it’s moving or thinking or healing, is a pattern of energy that began as light from the sun, which either found its way into a plant and then into you or entered you directly. And you depend on constant infusions of that energy to keep the flow, and the fun, going.
Keeping all that in mind can help take away some unnecessary fear and maybe even put an extra spring in your step the next time you step out into the light. Which I hope you’ll do soon.
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