The Nordic countries are no strangers to the long, dark winter.

Despite little to no daylight — plus months of frigid temperatures — people who live in northern Europe and above the Arctic Circle have learned how to cope mentally and physically with the annual onset of the winter blues, which can begin as early as October and last into April for some.

The winter solstice will occur Dec. 21, marking the shortest day and longest night of the year in the Northern Hemisphere. While sunlight increases daily after that, winter won't be over for a while yet.

The Associated Press spoke to experts in Norway, Sweden and Finland about the winter blues. Here's how they suggest looking for light, literally and figuratively, during the darkest months of the year:

Maintaining sleep and social habits are key

Dr. Timo Partonen, a research professor at the Finnish Institute for Health and Welfare, said the dark winter affects our circadian rhythm.

With limited daylight, our internal body clocks cannot reset or synchronize properly and it throws off our sleep. We may sleep longer in the winter, he said, but we don't wake up refreshed and can remain tired the rest of the day.

Partonen recommended trying a dawn simulator, sometimes known as a sunrise alarm clock, to gradually light up your bedroom and ease you awake.

In addition to being more tired, we're more likely to withdraw from others socially in the wintertime. We're more irritable, Partonen said, and more prone to fights with friends.

It's important to maintain our relationships, he said, because symptoms rarely improve in isolation.

And since keeping up with exercise is also key to combating the winter blues, consider inviting a friend along for a workout.

It could also help keep off the wintertime weight gain — typically 2 to 5 kilograms (4 to 11 pounds) a year, Partonen said — that's fed by cravings for carbohydrates, especially in the evenings.

Light therapy encouraged for a range of symptoms

Millions of people worldwide are estimated to suffer from seasonal depression. Also known as seasonal affective disorder, or SAD, patients typically have episodes of depression that begin in the fall and ease in the spring or summer. A milder form, subsyndromal SAD, is recognized by medical experts, and there’s also a summer variety of seasonal depression, though less is known about it.

Scientists are learning how specialized cells in our eyes turn the blue wavelength part of the light spectrum into neural signals affecting mood and alertness. Sunlight is loaded with the blue light, so when the cells absorb it, our brains’ alertness centers are activated and we feel more awake and possibly even happier.

Researcher Kathryn Roecklein at the University of Pittsburgh tested people with and without SAD to see how their eyes reacted to blue light. As a group, people with SAD were less sensitive to blue light than others, especially during winter months. That suggests a cause for wintertime depression.

In severe cases, people need clinical support and antidepressant medications. Christian Benedict, a pharmacology professor at Uppsala University in Sweden, suggests light therapy for people with SAD as well as those who have a milder case of the winter blues.

“It’s not like it’s a fate, an annual or a seasonal fate, and you cannot do anything about it,” Benedict said. “There are possibilities to affect it.”

A routine of morning light therapy, using devices that emit light about 20 times brighter than regular indoor light, can be beneficial for both people with and without SAD.

The light therapy helps to kickstart your circadian rhythm and increases serotonin in your brain, Benedict said.

Research supports using a light that’s about 10,000 lux, a measure of brightness, for 30 minutes every morning. Special lights run from $70 to $400, though some products marketed for SAD are not bright enough to be useful. Your insurance company might cover at least part of the cost if you’ve been diagnosed with SAD.

Partonen recommended using both a dawn simulator and a light therapy device each day before noon.

Yale has tested products and offers a list of recommendations, and the nonprofit Center for Environmental Therapeutics has a consumer guide to selecting a light.

Prioritizing a positive outlook as a survival strategy

And don't forget to, well, look on the bright side. It's crucial to embrace winter instead of dreading it, according to Ida Solhaug, an associate professor in psychology at the University of Tromsø, also known as the Arctic University of Norway — the world's northernmost university.

Prioritize a positive outlook as a survival strategy and learn to appreciate the change in seasons. It's a typical Norwegian way of thinking, she said, that can make all the difference when there's very little daylight for months.

“It's part of the culture,” she said.

And don't forget to take advantage of both outdoor and indoor hobbies, she said. Inside, channel hygge — the Danish obsession with getting cozy — and snuggle up on the couch with blankets and a movie.

But don't hibernate all winter. After the film finishes, head outside with a thermos for fika, the traditional Swedish coffee break. Even during cloudy days, a quick walk in the fresh air will help, she said. And if you're brave enough, do a cold plunge like many people in the Nordics.

Solhaug tries to jump into the frigid waters off the coast of Tromsø, an island 350 kilometers (217 miles) north of the Arctic Circle, at least once a week, adding that it makes her feel revitalized during the long winter.

“Challenge yourself to look for light in the darkness,” she said.

After all, as many Nordic people say, there’s no such thing as bad weather — only bad clothing.

Finland's President Alexander Stubb, too, had some tips for how to tackle Nordic winters. When asked in an interview with The Associated Press last month how to survive the cold season, he had some very specific advice.

“Take an ice bath and then followed up by a sauna and do one more ice bath, one more sauna, then a shower and go out there. You’ll manage,” Stubb said.

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Dazio reported from Berlin.