Cold weather and shortened days -- the most noticeable signs of winter's approach -- are affecting some students' moods and behavior, experts say.

Mary Anne Knapp, a clinical social worker and therapist at the Center for Counseling and Psychological Services (CAPS), estimated that 4 to 5 percent of Penn State students suffer from Seasonal Affective Disorder (SAD), and many more experience the milder symptoms of "winter blues."

SAD is triggered primarily by the shortening of daylight hours in the fall, associate professor of psychology Frederick Brown said. He said a part of the brain called the suprachiasmatic nucleus, which is involved in the timing of the body's internal functions, responds to the decreasing daylight hours by signaling certain physiological and psychological changes to occur.

"In some humans, it produces pseudo-hibernation behavior," he said, explaining that it is similar to the way hibernating animals prepare for winter. "There is an increased tendency to eat more carbohydrates, to slow down activity and to want more sleep."

He said it is common for people to experience these symptoms mildly as "winter blues."

"I think there is a high proportion of people -- probably one-fourth of people in the United States -- who have winter blues," he said. "They have the 'blahs;' they feel kind of funky, but they're still grooving, just not with the same degree of vigor as over the summer."

But SAD, which is much more severe, can completely change a person's behavior and mood.

"Some people will sleep for long periods of time, and they become weepy and not very alert," he said.

Knapp said SAD can be distinguished from general depression because its symptoms are seasonal.

"SAD is [diagnosed] if someone has depressive symptoms that happen during fall and winter and that occur for a couple of years in a row," she said.

Brown said that in general, symptoms of SAD are more severe among residents of higher latitudes because the change from summer lighting to winter lighting is more drastic.

"For example, Sweden suffers from the highest suicide rate in the world, and the people of Finland are noted as having a depressing demeanor," he said.

Knapp said this fact can even be observed in the United States alone.

"Only about 1 to 2 percent of Florida's population suffers from SAD, while about 9 percent of Alaska's population suffers from it," she said.

Both Brown and Knapp agreed that people living in this region are very susceptible to SAD.

"An area like Pennsylvania, which is very green in the summertime, is much more drab and gray after the leaves drop in the fall," he said.

However, he said that SAD occurs less frequently in areas such as the Southwest because the desert causes glare, making things brighter.

"A colleague of mine in Reno, which is at the same latitude as us, finds no SAD there because a greater amount of sunlight is mirrored off the sand," he said.

He said glare also occurs in other areas due to snow cover, which might help alleviate symptoms of SAD in the winter.

"My hypothesis is that SAD tends to lift in two ways: when snow blankets the ground and after December when the days start to lengthen again," he said. "In these situations you start to get a reduction in [symptoms]."

He said "reverse SAD" also exists, although it is extremely rare.

"A small proportion of SAD sufferers are affected in the summer, not the winter," he said.

He also said women tend to suffer from SAD more often than men because they are generally more sensitive to changes in illumination.

"I hate the winter," Laura Robilotta (sophomore-premedicine) said. "When it gets cold, I just sleep and mope."

Brown said the best way to cure SAD is to become exposed to more light. He said both natural and artificial light will help, but he recommends natural light because it is stronger.

"Even on the stormiest day, it is still much brighter outside than it is indoors under artificial illumination," he said. "Most people are used to about 500 to 1,000 lux [a measure of illumination] indoors, but they can get up to 100,000 lux outdoors at noon on a sunny day and even up to 10,000 on the most extreme, black, stormy days."

He suggested that people with SAD symptoms go outside every day, about midday, for at least half an hour.

He also said it is a good idea to keep more lights on inside to make things brighter.

Knapp suggested more exercise and more exposure to daylight for mild symptoms, but said light therapy is best for those with severe SAD.

"Light therapy involves daily exposure to the full spectrum of light," she said.

She said light boxes or light banks provide a full spectrum, and a small one can be purchased for less than $200.

As a cheaper alternative, people can also make their own by buying full spectrum lights of 10,000 lux, which are sold at Wal-Mart, and placing them in a frame.

She said the person should sit in front of the light box for 30 minutes each day, preferably in the morning.

Brown added that another method of SAD therapy is a change in environment.

"There is an easy way to identify SAD -- take the person to the Bahamas," he said with a laugh.

"I guarantee the symptoms will lift in one or two hours."