MINNEAPOLIS (WCCO) – Our daylight hours are getting shorter and the nights are getting longer, and the WCCO Morning Show took a look at the science behind why some people get depressed in the winter.

Estimates are that one in ten Minnesotans are affected by seasonal affective disorder (or SAD). The good news is that it can be easily treated.

Minnesota winters offer a change of pace with things like snow, shorter days and longer nights. Many people find that like clockwork, right around this time of year they start feeling blue.

It might not be the cold weather tempting you to stay in bed. You may have seasonal depression or seasonal affective disorder.

“A number of the symptoms of seasonal affective disorder are relatively similar to symptoms of mild or even major depression,” said Dr. Charles Shulz, head of psychiatry at the University of Minnesota. “Sadness, lack of energy, changes in appetite, lack of interest, not a very hopeful outlook.”

One suspected cause of SAD is related to our internal clocks called our circadian rhythm.

“All living creatures operate on a 24-hour clock,” said Dr. Michael Howell, who deals with sleep medicine at Fairview Clinics. “What resets our circadian rhythm every morning is the first exposure to sun, which for the most part we don’t receive, especially in Minnesota in the wintertime.”

Less light can throw off our rhythms and cause the onset of SAD. One of the most effective ways to treat it is bright light therapy. Light boxes can cost about $200 new. You can find them online or at a medical supply story.

“It’s extremely bright and somewhat noxious, which is telling you that it’s working,” said Howell. “This light is 10,000 lux, which is equivalent to the light that you get when you’re outside and you’re receiving natural sunlight.”

Unfortunately, our 24-hour society makes demands on our schedules that cause us to disrupt our natural sleep schedule.

“This is a pervasive problem,” said Howell. “If you ever have trouble falling asleep at night but also want to hit the snooze alarm in the morning, you have a circadian rhythm delay. It’s particularly problematic in young people — adolescents and college students — and also amongst people who have to get up early to go to work.”

And some studies show that those living in Minnesota have the highest rates of seasonal affective disorder.

“We do know from epidemiology studies that seasonal affective disorders is about 2 percent of the population in Florida and about 11 percent of the population in Minnesota, Norway and Alaska,” said Shulz. “It does have a lot to do with the really short days that we have. It’s a real environmental factor.”

Those with seasonal affective disorder come out of it once the days start really getting longer in April and May.