Without the sun, there is no life. The sun stirs our atmosphere, warms our oceans, and gives energy to plants that generate oxygen and food.
The sun also influences our body and mind in ways that modern science is only beginning to appreciate.
For most of human history, people revered the sun, even worshipped it as a deity. For the ancient Greeks, the sun god was Apollo, who, among many other things, taught men the art of medicine.
Though these rituals fell out of fashion, the Industrial Revolution served as a stark reminder of the sun's importance to human health. As factories became more productive, many cities were blanketed by thick clouds of soot and smog, blocking out the sun. Doctors across the Western world began to observe a similar pattern: Rural children developed normally, while kids in cities were riddled with rickets—a devastating disease wherein bones become weak and warped. Their bodies were literally starving for sunshine.
Today, we know that rickets is caused by a deficiency in vitamin D, sometimes known as the "sunshine vitamin."
Despite the name, scientists say vitamin D is actually a hormone, with a chemical signature similar to estrogen and cortisol. Our bodies can't make vitamin D on their own, but can synthesize it when our skin is exposed to ultraviolet (UV) radiation.
Ancient doctors didn't know about vitamin D, but they did observe curative powers from fresh air and sunshine. Hippocrates, the father of medicine, designed sun exposure regimens to treat various ailments. Up until the late 1800s, doctors were prescribing sunshine to treat patients with tuberculosis and other diseases.
Yet, ever since the discovery of vitamin D, there has been much more emphasis on supplementation than sunlight. Very few foods (mostly fish) contain vitamin D, so, since the 1930s, food manufacturers have been fortifying our milk, juice, and cereals with this nutrient to prevent rickets from creeping back.
We may have conquered rickets, but a new school of thought says we are missing out on many of the benefits the sun has to offer.
For much of the last century, we've been told to shun the sun, due to the risk of cancer and skin damage. Backed by decades of research, dermatologists warn that we should avoid direct rays. Experts encourage us to get our vitamin D from the safety of a supplement or through dietary sources.
But more recent research is challenging this notion and casting a new light on the links between sun exposure and cancer. Two studies in particular, from the Journal of the National Cancer Institute, reported that people who got daily sun exposure had a lower risk of getting non-Hodgkin's lymphoma. They also observed increased survival rates in patients with early-stage melanoma.
Such research has prompted organizations that previously warned against sun exposure—such as the World Health Organization and the British Association of Dermatologists—to take a more balanced approach. Even in Australia, which has the highest melanoma rate in the world, the country's Cancer Council is now recommending that everybody get more regular sun exposure.
The rationale behind this sun-friendly revival is that small, consistent doses of sunlight have been shown to help our bodies build a defense against the sun's damaging effects, while allowing us to soak up more of its benefits.
Dr. Michael Holick is an endocrinologist who specializes in vitamin D at Boston University Medical Center. He's a big proponent of supplementation, but says a pill still can't provide what the sun can.
"This sun-phobic atmosphere has been promoted for so long," Holick said. "But the abstinence recommendation of not being exposed to one direct ray of sunlight for your entire life defies good logic."
While sun avoidance may lower your risk of skin cancer, Holick says it also raises your risk of other diseases, such as breast cancer, heart disease, and colon cancer.
But sunshine prescriptions are extremely controversial in modern medicine. In Holick's 2004 book "The UV Advantage: The Medical Breakthrough That Shows How to Harness the Power of the Sun for Your Health," he recommended that people aim for five to 10 minutes of direct sun exposure, two to three times per week. His superiors at Boston University told him to either rescind his recommendation, or step down from his position in the dermatology department.
Holick chose to keep his sun exposure advice, and remains a professor of medicine, physiology, and biophysics, as well as the director of the Heliotherapy, Light, and Skin Research Center at the university's medical center.
Holick says many of his fellow physicians have been slow to change because their generation was trained with the notion that even a little sun exposure can damage DNA and the genes that regulate cell growth, harming the control mechanisms that prevent a cell from becoming malignant.
But he says this position fails to see the bigger picture. He points to a recent study from the U.K. in which very light-skinned people (the complexion most susceptible to sun damage) were exposed to simulated sunlight two to three times a week for six weeks.
"There was some DNA damage, but what was remarkable was that at the end of the study, it looked like there were mechanisms at play to help correct the DNA damage," Holick said.
Beyond Vitamin D
Vitamin D isn't the only benefit we get from the sun. When photons from the sun penetrate our skin, a number of chemical changes occur. In addition to vitamin D, the sun's influence creates nitric oxide, which causes relaxation of blood vessels and lowers blood pressure.
UV radiation can also stimulate genes in the skin cells that cause the production of other hormones that may help modulate our immune system, as well as beta-endorphin, a substance that scientists believe may be what gives us that euphoric feeling when we bask in sunlight.
"There is good evidence that the lower the latitude that you live [in the Northern Hemisphere], the lower your risk for high blood pressure, having a heart attack, multiple sclerosis, Type 1 diabetes, infectious diseases, cognitive dysfunction, and the list goes on," Holick said.
And while the sun is often associated with skin damage, in small doses it may actually heal many skin problems. Dr. Bobby Buka, a dermatologist based in New York, says inflammatory skin conditions such as psoriasis, eczema, and acne can benefit from UV radiation.
Because the quality of direct sun exposure can vary dramatically from day to day and place to place, Buka treats his patients with special lamps that emit a narrow band of UVB radiation. It doesn't take much: from 30 seconds to three minutes, two or three times a week. The initial dose is related to skin type. A pale redhead, for example, can only tolerate brief exposure, while those with darker skin tones can take much more.
Sun exposure can have a similar effect and may even prevent inflammatory skin conditions from erupting. While Buka cautions people to limit the amount of sun they're exposed to, he has observed that those who live closer to the equator are less likely to get the conditions he treats.
"Most of those patients don't need to see a dermatologist because they have milder cases that are already being handled by the ambient light," he said.
A Proper Dose
Of course, the sun is not a totally benign orb. The Greeks believed Apollo could provide health, but could also deliver disease. To get the sun's benefits without its harsh consequences, you have to be mindful of exposure.
Not all sunlight is created equal. When it comes to making vitamin D, for example, there are lots of factors to consider, such as your skin color, where you live, ozone and hydrocarbon levels in the atmosphere (which can filter and reflect UV rays), time of year, and time of day.
"You essentially make no vitamin D before 9 a.m. and after 4 p.m. or 5 p.m., even if you're at the equator with the sun shining brightly," Holick said.
Holick says sun exposure during these times—the early morning and late afternoon—are worse for your skin due to the UVA radiation. "The UVA radiation that you're exposed to is blasting your immune system and your dermis, which is causing wrinkles and increasing the likelihood of melanomas and skin cancer," he said.
To take the guesswork out of vitamin D production, Holick and his team invented an app that tells you the most beneficial times to seek the sun wherever you live.
While Holick wants people to get more sun, he still urges caution. Wear a hat and apply sunscreen to your face—the part of the body most exposed to the sun and therefore most susceptible to damage. And always wear sunglasses to offset risks of cataracts and inflammation.
"It's just like everything else in life: You have to do it in moderation," Holick said. "And you need to understand the consequences of what you're doing."