Most Minnesotans can probably relate to the winter morning thought, "I don't want to get up; I just want to stay snuggled in my warm, cozy bed!" But for people with seasonal affective disorder (SAD), getting out of bed -- and all the routines and responsibilities that follow -- can be a serious challenge in winter months.

"Everything just seemed like a mountain," said Eagan resident Shelley Lanns, who realized she had SAD about five years ago. Every year when the cold rolled in, she dreaded peeling herself from bed, finding the energy to shower and even going in to work. These daily tasks were difficult on her best days, and on her worst days they were simply impossible.

Although Lanns' case was on the more debilitating end of the spectrum, experts say that up to 10 percent of people suffer from a seasonal depression that ranges from mild to severe.

"It's more common than you would probably imagine," said Jane Hovland, a licensed psychologist and associate professor in behavioral sciences at the University of Minnesota Medical School in Duluth.

The root of the problem, she said, is probably a lack of light that results in out-of-balance body rhythms. Light stimulates the body to produce certain chemicals, including serotonin and melatonin, that affect mood, energy levels and much more. Hovland has seen significant improvement in patients who moved from a home nestled in the woods to a house with lots of south-facing windows.

The first researcher credited with describing SAD, psychiatrist Norman Rosenthal, offers an explanation in his book "Winter Blues": "Over hundreds of thousands of years, the architecture of our bodies has been shaped by the seasons and we have developed mechanisms to deal with the changes they bring. Sometimes, however, those mechanisms break down and cause us trouble.

"The effects of the seasons on humans have been well known through the centuries to artists, poets and songwriters," he writes. "In recent years, science and medical practice have caught up to some extent with language, culture and the arts, and the medical importance of the seasons is starting to be appreciated."

SAD is a subcategory under the umbrella of depression, so it has the same symptoms as classic depression, said Alan Steed, a psychologist with Allina Medical Clinic. The difference is that the symptoms occur specifically in the winter months, often starting in fall and ending in spring.

Signs include: oversleeping, fatigue, difficulty concentrating, withdrawal from family members and friends, irritability, anxiety, weight gain, guilt, pessimism, hopelessness, craving carbohydrates and sugar, lowered sex drive and headaches. Women are up to four times more likely to be affected by SAD than are men, he said, and most people with the disorder have a close relative who has depression.

Fortunately, since light is at the heart of the problem, it also provides an easy solution. Light therapy is about 85 percent effective at improving how people with SAD feel, Steed said.

It provided an immediate improvement for Lanns. "I noticed a difference the first day I did it," she said. "It gives me a little more energy and more focus." She's also made several helpful lifestyle changes, she said, including exercising regularly, eating healthier, connecting with friends, getting outside more, seeing a therapist and taking medication.

Sarah Moran is a freelance health writer in Minneapolis.