Most people have heard about seasonal affective disorder, or SAD, in which the gloomy, cold, dark season of winter causes a depressed mood and other health concerns such as weight gain, excess sleep and lethargy. Numerous studies about the impact of weather on human health have revealed that the opposite is true as well: Sunshine and warm weather improve a person’s mood, raise energy levels and boost mental functionality.

But recent evidence about the benefits of vitamin D, which is produced in the body through exposure to sunlight, has demonstrated that sunlight improves our physiological well-being in addition to our emotional state. So why have residual guilt about spending all day on Old Campus?

On an emotional level, sunshine and warm temperatures improve optimism. Sun-induced contentment is magnified in the springtime because we have been deprived of sunlight throughout the winter. In fact, this effect is so powerful that it operates on a subconscious level; a recent study in the Journal of Finance found that stocks traded on sunny days were more profitable than stocks traded in cloudy weather.

But the sun’s rays affect more than our attitude: They also sharpen our minds. A recent study from Loyola University found that people working in sunlight had better short-term memory and were more flexible and creative in their thinking. Research published in the Journal of Neurology, Neurosurgery and Psychiatry tested men for mental agility and found that those with higher levels of vitamin D performed consistently better than those with lower levels.

Physically, time in the sun strengthens the immune system and aids milk production in lactating women. Sunlight has been found to have germicidic effects as well; exposure to the sun’s ultraviolet rays kills bacteria and acts as a natural antiseptic. In addition, oxygen consumption of cells drastically improves when they are exposed to the sun, boosting energy and endurance for daily activities.

A stint in the sun also offers long-term advantages in the form of vitamin D. Vitamin D has been proven to keep the brain in top shape as we age. For people who want to retire to Florida in their golden years, recent research has shown that vitamin D’s preservative benefits are even more significant in people over the age of 60. Furthermore, numerous studies have proven that vitamin D protects against cancer, rickets, osteoporosis and diabetes. And a lack of vitamin D brought on by insufficient exposure to sunlight has been linked with a terrifyingly large number of ailments: neuro-degenerative diseases, allergies, bone diseases, multiple sclerosis, diabetes and psoriasis.

While some may argue that the health benefits of sunlight are outweighed by the risks of skin cancer and more rapid aging, recent studies have found that some ultraviolet exposure actually prevents cancer. One study calculated that people living just below the equator in Australia produced more vitamin D than people in Britain. Even though the rates of skin cancer, as well as internal cancers such as colon cancer, lung cancer, breast cancer and prostate cancer, are higher in Australia, people in Australia were less likely to die from the diseases. Another study found that cancer patients who have surgery in the summer and who consume vitamin D supplements are twice as likely to be alive five years later than those who had their surgery in winter with little or no supplemental vitamin D.

Finally, what’s best of all is that all of the physical and mental benefits caused by sunny and warm weather don’t level off as you spend more time outside. So as long as you’re not getting burned on Old Campus — which will counteract sunshine’s benefits — stay outside as long as you want and enjoy the weeks before finals!

Rebecca Stern is a sophomore in Berkeley College.

Correction: April 14, 2010

An earlier version of this column misstated what the acronym SAD stands for; it is “seasonal affective disorder,” not “seasonal acquired depression.”