On dreary winter days, Barbara Sartorio would rather stay in bed, pull up the covers and sleep the day away.

“It’s really hard for me to get up in the morning when it’s dark outside,” said the 28-year-old Longview woman. “I just don’t feel like doing anything.”

Sartorio recently was diagnosed with seasonal affective disorder — SAD — a type of depression linked to a biochemical imbalance in the brain triggered by shorter daylight hours and a lack of sunlight in the winter. Here in the often-gloomy Northwest, as much as 20 percent of the population may be affected, said Dr. Amy Aronsky, medical director at St. John Medical Center’s sleep center.

“We absolutely have a higher instance here,” Aronsky said. “With the dark, rainy type of environment that we see for seven months, you’re more likely to develop the depression.”

With the change from Daylight Savings to Standard time and shorter winter days,

it’s good to know there are treatment options out there — even though researchers are still somewhat in the dark on the disorder.

Treatment for SAD can be as simple as using a “light box” — very bright light, usually from a special fluorescent lamp that emits white or blue light — for 20 to 30 minutes each day. More severe cases may require patients to take antidepressants and seek counseling.

Sartorio has been using a light box for a little more than a week, and she said it’s already making a difference in her mood and outlook.

“I get up and I put it on, maybe while I eat my breakfast or do a crossword puzzle,” she said. “I have had a lot more energy. I don’t think, ‘Ooof, I have to get to work.’ It just makes my day start out better.”

Sartorio’s swift response to the light box therapy isn’t unusual, said Dr. Robert Axelrod, a psychiatrist at St. John’s Peace of Mind mental health clinic for outpatients.

“People who are responsive to a light box respond quite quickly,” he said. “For people who really have (SAD), the treatment results are pretty impressive.”

Less daylight in the winter can throw out of whack some people’s biological internal clock — or circadian rhythm — causing them to be out of step with their daily schedule and leading to SAD, according to the American Psychiatric Association. Melatonin, a sleep-related hormone linked to depression, also has been associated with SAD. Melatonin is produced at increased levels in the dark, so when the days are shorter, more melatonin is produced.

Research has proven that bright light makes a difference to the brain chemistry, although the exact way it affects SAD is unknown, Axelrod said.

“Essentially, the light is received by the optic nerve in the back of the eye,” he explained. Where the two optic nerves meet, “that has a direct neuron connection to the section of the brain that controls your circadian cycles and melatonin. That’s the amount we understand.”

Both Aronsky and Axelrod recommend the use of light therapy as the first step for treating SAD.

“So many patients are looking for nonpharmacological solutions, and the light box offers that,” Aronsky said.

“If people feel like they have seasonal depression, it’s pretty harmless to get a light box on your own, if you can afford it,” Axelrod said. “If it responds, that’s all it takes. There are no side effects, and it’s a lot faster and cheaper (than conventional medications).”

Aronsky and Axelrod said lights should be 10,000 lux illumination. Tanning beds are not recommended for treatment, Axelrod said.

Though symptoms for SAD are sometimes similar to other textbook depressions, Aronsky said the timing of the depression is the telling sign.

“Regular depression doesn’t have seasonal boundaries,” she said. “If your mood lifts during the warmer months, it’s most likely SAD.”