For many Canadians, winter is the season of our discontent. Fortunately, there's light at the end of a long, cold, dark tunnel.

The sleep-deprived are waking up to warmer weather and brighter days, and biological rhythms will readjust.

"The cold makes people feel tired, more irritable, and they're often going to and from work in the dark. That's starting to lift now, as will these bone-chilling temperatures," said Dr. James MacFarlane, a sleep specialist with Toronto's SleepMed clinic.

"I think that's going to lead to an improvement. You'll want to be out and part of the world again."

As many as 35 per cent of Canadians complain of having the "winter blues," according to the Centre for Addiction and Mental Health. Another 10 to 15 per cent have a mild form of seasonal depression, while about two to five per cent of Canadians will have a severe, clinical form of Seasonal Affective Disorder (SAD).

It often starts with fatigue, then symptoms of sadness, lethargy, apathy and depression, said Dr. Robert Levitan, the head of depression research at CAMH.

Coming off the coldest February recorded in Quebec and southern Ontario, it's little surprise the chilling effect can give way to frosty moods and feelings of sluggishness.

The onset of low energy levels as temperatures dip and mornings darken might be a vestige of a more primitive past.

Circadian rhythms out of whack

"A lot of us in the field think this is an evolutionary mechanism," said Levitan, who specializes in mood and anxiety disorders. "It's in our genes. They're designed to turn us off in the fall-winter period to conserve energy, then turn us back on in the spring-summer, very much like hibernating animals."

 Grace Kaiche

Grace Kaiche has found that using a special light box has helped reduce the effects of Seasonal Affective Disorder. (CBC)

But what's to blame for these physiological effects?

Our biological clocks, or circadian rhythms, have much to do with our listlessness come winter.

Winter throws those natural body rhythms out of whack as the increased darkness during the day causes people's "sleep hygiene" to deteriorate, according to Dr. Richard Leung, director of the sleep laboratory at Toronto's St. Michael's Hospital.

Melatonin, the "hormone of darkness," amps up during these longer dark cycles and promotes sleepiness, he explained.

'I'm finding that my patients just aren't going out and exercising. They're saying it's just too cold' - Dr. Mel Borins, University of Toronto faculty of medicine

"People also have the temptation to go to bed earlier because there's nothing to do," Leung said. "By the same token, they sleep in later than normal because the darkness lasts longer, and find it difficult to wake up without sunlight shining through the windows."

Those irregular patterns can snowball, Leung explained, with sleep-deprived people sneaking naps to compensate, then struggling to catch quality shuteye later.

Multiple systems in the brain

Levitan said that when SAD was first officially described in psychiatric literature in 1984, melatonin was a prime suspect.

But changes in the light-sensitive hormone, which the body secretes naturally, couldn't sufficiently account for depression across the seasons.

Dr. Robert Levitan

Dr. Robert Levitan, a psychiatrist at the Centre for Addiction and Mental Health (CAMH) in Toronto, recommends light therapy to combat SAD. (Manmeet Ahluwalia/CBC)

Researchers next looked at how changes in the brain chemical serotonin, as well as SAD patients' reaction to depletion of tryptophan (the natural precursor of serotonin), affected moods.

"We know [serotonin levels] are changing in the brain quite profoundly across the seasons, but it's probably not just serotonin because we know that medications that influence other brain chemicals are also able to treat seasonal symptoms," Levitan said.

Studies of the neurotransmitter dopamine seemed to predict important aspects of SAD as well, he said.

"So it's not just one system in the brain, but probably multiple systems that are regulated together."

There are behavioural factors at play, too. While exercise has been shown to boost feel-good endorphin levels, winter malaise can deter people from bundling up to go for a jog.

"I'm finding that my patients just aren't going out and exercising," said Dr. Mel Borins, an associate professor at the University of Toronto's faculty of medicine. "They're saying it's just too cold to go out."

He recommends his patients walk inside a mall or explore a subterranean pedestrian system such as Toronto's PATH network.

The sunshine vitamin

Borins, who writes about happiness and alternative medicine, has been seeing more patients with vitamin D deficiencies because the lack of sunlight and the below-zero temperatures keep them indoors.

si-snowscraper

Winter weather can cause increased irritability, but doctors say outdoor physical activity, exposure to sunshine and taking vitamin D can help improve moods. (Associated Press)

People who suffer from a seasonal disorder can also try light therapy, purchasing a full-spectrum light box and exposing their skin to the lamp, which mimics sunlight, for half an hour a day.​

"Sunshine is really important to people's health, and a lot of people aren't getting vitamin D from the sun because it's so gloomy out," Borins said. He noted that vitamin D levels have been shown to have a connection with mood changes.

Weight gain

People experiencing the "winter blahs" tend to withdraw socially, which could lead to feelings of isolation or depression, said Toronto-based psychotherapist Tasha Shauli.

Oversleeping or wanting to stay in bed longer are common behaviours, as is eating poorly.

"Some people describe a decrease in appetite, but a lot of people can have more severe cravings for sugary foods and carbohydrates," she said.

"That can cause depressive effects of not looking the best or feeling the best, having that weight gain, and then just a general lack of motivation for doing activities that people tend to enjoy."

The cold also takes a physical toll, she said, as we exert more energy to keep our bodies warm. Factor in driveway shovelling and having to trudge through slush in heavy winter gear, and it's no wonder energy stores get depleted.

If SAD or seasonal depression is affecting your daily functioning at home or work, doctors urge you to seek help immediately. For more information on SAD and treatment options, visit the CAMH website.