By Markham Heid
May 21, 2014
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Skip the coffee and St. John's wort. Soaking up a little sun this Memorial Day weekend could work wonders for your mood, energy levels, willpower, sleep schedule, and appetite. It could even help your body fend off some of the most common killer diseases, research suggests. Here's how.

When Sunlight Hits Your Eyes

Photoreceptors in your eyes react to sunlight by sending messages to parts of your brain that regulate your body's serotonin levels, explains Alex Korb, Ph.D., a neuroscientist and post-doctoral researcher at UCLA. These messages instruct your brain and body to conserve serotonin instead of converting it into other brain chemicals, Korb explains. Why that matters: Serotonin plays a big role in setting your body's circadian clock, which manages your sleep and hunger cycles, and also ties into your cell health, hormone production, and other biological functions, Korb says.

When serotonin levels rise, studies show you tend to feel alert, energized, and happy, he adds. French researchers even found women were more likely to say yes to a date request on clear days as opposed to cloudy ones, crediting a sun-triggered boost in mood. (Selective serotonin reuptake inhibitors, or SSRIs, are common antidepressants that basically mimic sunlight's ability to help your brain produce and conserve serotonin, Korb adds.)

Exposing your eyes to sun-strength light for at least 20 minutes in the morning is your best bet in aligning your wake-sleep clock with daytime hours. You also want to avoid bright light at night, which fools your brain into believing it's daytime, Korb adds. (One study found long-term night-shift workers suffer from higher rates of breast cancer, which the authors blamed on funky levels of serotonin and it's partner hormone, melatonin.)

You don't need to stare at the sun for your eyes to absorb its light though, Korb explains. Sitting close to a window or within a few feet of bright sunlight will trigger serotonin-producing reactions. Studies have also shown that a light box that mimics the sun can boost serotonin levels, Korb adds.

When Sunlight Touches Your Skin

Nitric oxide, a chemical stored in the outermost layers of your skin, reacts to the sun's ultraviolet rays by widening your blood vessels, shows research from the U.K. As a result, your blood pressure drops, your heart rate slows, and you feel more relaxed. Separate research from the University of Alabama at Birmingham has also linked this improvement in blood flow to better mental performance.

The sun's UV light contains b photons-light particles that penetrate your skin and trigger the release of a skin cholesterol that your body uses to produce vitamin D, shows research from the Boston University Medical Center. And vitamin D is necessary for serotonin production. There's evidence that proper serotonin and vitamin D levels play a part in your DNA health, and that low D levels are linked to higher rates of heart disease, cancer, Alzheimer's, stroke, and diabetes.

While some foods contain D, Korb says there aren't any nutritional sources that pack enough of it. Your goal then? Ten to 15 minutes of midday sunlight on bare arms, legs, and shoulders every day, Korb says. And you can hold off on sunblock: Fifteen minutes is enough to help your body produce the loads of vitamin D it needs without increasing your risk for skin cancer, research suggests.

Long-Term Effects

The interactions between sunlight, vitamin D, serotonin, and your circadian clock are complex, but your health and happiness are dependent on these factors working in harmony, Korb explains. Without enough sun exposure, serotonin levels fluctuate erratically, knocking your circadian clock out of whack. That could leave you feeling sleepy during the day, wired at night, hungry at odd hours (or all the time!), and unable to think clearly, Korb says.

"There's a lot of research on seasonal affective disorder (depression that crops up during times of the year when you're not exposed to much sunlight)," Korb explains. During the winter, the sun spends a smaller fraction of the day at a height where its UV rays can penetrate the Earth's atmosphere, studies show. That means there's a reduced window when your skin can absorb the light it needs to manufacture vitamin D. In fact, some studies have indicated up to 80 percent of the world's population is vitamin D deficient during the colder months. Taking a 1,000 IU vitamin D supplement during the winter can ward off disease and depression, studies show.