Why sun is good for you

Several studies have suggested that suddenly getting a lot of sun is more dangerous then steady exposure over time. There's also evidence that exposure when you're young — perhaps before your 20th birthday — matters most.

A large Scandinavian study of melanoma risk published in the Journal of the National Cancer Institute in found that adolescence is the most dangerous time to get a sunburn. Recent sun exposure doesn't seem to be associated with basal cell carcinoma, the mildest form of skin cancer.

Squamous cell carcinoma appears to be different. Cumulative and recent exposure to sunlight at any age is strongly associated with actinic keratoses, scaly growths on the skin that are a risk factor for that type of skin cancer. The same DNA-damaging, sunburn-causing UVB wavelengths that sunscreens are designed to block also do some good: They kick off the chemical and metabolic chain reaction that produces vitamin D.

Research shows that many people have low vitamin D levels. There is a well-documented relationship between low vitamin D levels and poor bone health. Now links have been made to everything from multiple sclerosis to prostate cancer. Getting some sun may also shake off the wintertime blues: Research suggests that light hitting your skin, not just your eyes, helps reverse seasonal affective disorder SAD. Moreover, being outside gets us golfing, gardening, and engaging in other types of physical activity.

Nobody wants to get skin cancer, but we've gone from sun worship to sun dread. Stern and others say there is a middle way that includes using a sunscreen with a sun protection factor SPF of at least 15 when you're outside for an extended period and wearing a hat and shirt around midday.

So when summer's here, get outside and enjoy it! As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

The trick is getting an appropriate amount without boosting your risk. In general, target about 10 to 20 minutes of exposure on non-sunscreened skin every day. Holick notes that it's much better to have a small amount of sun time daily rather than a sun binge on a single day, which might cause sunburn.

If only there were an app for that, you might think. Your wish is granted: Check out dminder , which lets you input skin tone, age, weight, and amount of skin exposed. Using weather and season information, the app tracks your ideal sun time for anywhere in the world. On the non-techie side, aim to have the sun hit shoulders, arms, or legs instead of your more wrinkle-prone face and neck. If you're living in a northern locale, where sunlight is scant for a chunk of the year, you might want to consider a light box , which mimics sunlight and is often used for seasonal affective disorder.

If you're gradually increasing your sunshine time, be sure to also up your awareness of sun-related damage. Keep an eye on moles and blemishes , and check out any changes that seem notable. Most of all, unless you actually are a vampire no judgment , incorporate a little sun when you can, at a sensible level, and it's likely you'll start seeing some benefits, Holick believes.

SELF does not provide medical advice, diagnosis, or treatment. Any information published on this website or by this brand is not intended as a substitute for medical advice, and you should not take any action before consulting with a healthcare professional. Elizabeth Millard is a freelance writer specializing in health and fitness, as well as an ACE-certified personal trainer and Yoga Alliance-registered yoga teacher.

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Even Hippocrates believed that the changing seasons had something to do with health—and that the key was how much available daylight there was during different times of the year. Many centuries later, it's clear he was on to something. As people spend more time indoors staring at computer and television screens, scientists are starting to appreciate how exposure to sunlight affects various body systems.

The most interesting support for our dependence on daylight emerged with a condition called Seasonal Affective Disorder , or SAD. The term was coined by Dr. Normal Rosenthal at Georgetown University to describe the so-called winter blues: the lethargy and feelings of sadness and hopelessness that come when the weather forces people to spend more time indoors and the season provides little opportunity for exposure to natural light.

Some people have speculated that our modern lifestyle, which keeps people indoors under artificial light for so many hours, may be encouraging a form of SAD year-round. Rosenthal found that while not everyone is as strongly affected by a lack of sunlight, for the people who are, light boxes that blast a few minutes of bright light in the frequency of natural sunlight each morning can help to elevate mood and re-energize them to face the day.

Studies of shift workers also support the possible role that exposure to sunlight has on mood. That can have domino effects on nearly everything: how we break down energy from food, how strong our immune systems are and the vast array of brain chemicals and other substances that contribute to mood, weight, energy and more. Normally, people produce more melatonin toward the evening, as the body gets ready for sleep.

As more light creeps in during the morning, the levels of the hormone start dropping again. In winter months when the days are shorter, melatonin levels may peak earlier or later in the day, which can lead to some of the mood changes linked to SAD. Studies in shift workers found that less melatonin may also lead to lower levels of important chemicals the body uses to repair DNA.

That could potentially lead to more mutated cells that can trigger cancer. Some studies also suggest that the light cycle may regulate the production of blood stem cells from the bone marrow. More research here is needed, but that could be important for the timing of bone marrow transplants for cancer patients, and hitting the transplant at just the right time of the light cycle may improve the chances of harvesting enough cells from donors.

Other work found that the dreaded risk of rejection of transplanted bone marrow cells might also be avoided with the help of light — in this case, ultraviolet light. Scientists treating mice who received skin transplants found that zapping the transplanted cells with UV light eliminated the group of cells most responsible for triggering rejection reactions. The strongest support for the role of sunlight in health, however, comes from its effect on mood.

Many antidepressants work by boosting levels of serotonin among brain neurons.