The Nordic countries are no stranger 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 awhile 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:

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 lbs) a year, Partonen said — that's fed by cravings for carbohydrates, especially in the evenings.

Eating carbohydrates regulates serotonin, which controls our mood and can be naturally produced by exposure to light.

So when there's less daylight in the winter months, our serotonin levels decrease.

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 wakeful and possibly even happier.

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.

But all experts agree that exercising outside will help banish the winter blues.