A study released this week by the Canadian Institutes of Health Research, coinciding with Blue Monday, finds more than 900,000 Canadians are diagnosed with seasonal affective disorder. Almost as surprising as this high number is that most of the sufferers, who face depression and lack of energy in the winter months, don’t suffer these symptoms at any other time.

“They really suffer only during this time of year,” said Dr. Marc Hébert of the Institute. “During the spring and summer times, they can feel very good.”

Symptoms of seasonal depression include downturns in mood (boredom, sadness, irritability, anxiousness); a tendency to overeat and oversleep; drowsiness during the daytime; lack of energy; difficulty completing tasks; and loss of interest in favourite activities.

The depression most commonly strikes those who live in wintery areas with short daytimes, and is also common in women, people aged 15 to 55, and those with other sufferers in their immediate family.

Hébert notes that seasonal depression can strike as early as September, with cases increasing in October, November and December. “Some people’s worst month is November, when it’s raining all the time,” he said.

“In my research, in July there were three weeks ago with rain in Quebec. The people in our study were in remission in April, May, but went back to depression in July because of the weather.”

Aside from the 900,000 diagnoses, Hébert estimates that 20-25 per cent of the Canadian population is affected at least mildly by the seasonal activity. While the causes of winter depression are not certain, Hébert suggests that lack of exposure to sunlight impacts the brain’s ability to produce serotonin, a chemical that affects mood.

“Most people get a couple of hours of natural daylight exposure during the summertime but only 30 minutes in the winter. For some people maybe these 30 minutes are not sufficient.”

He continued, “If you take an anti-depressant medication, it will increase your level of serotonin. Sunlight seems to do the same thing. The solution for these people is to get more natural light, or bright artificial light that will mimic the natural sunlight.”

The Institute finds that 2-3 per cent of the population is affected severely enough to seek medical help, where treatment can include dawn simulation, antidepressants, counseling, and bright light treatment. Others experience a milder form of the disorder.

“It’s said that for depression, staying active and getting exercise will improve mood,” said Hébert.“It certainly works, but it’s certainly more difficult in the wintertime to be more active than the summertime.”