As the days get shorter, and the nights longer, a lot of people experience minor changes in personality, things like lethargy or sleeping longer become the norm. Something we push through on a yearly basis as we lose sunlight.
But while we commonly call it Seasonal Affected Disorder (SAD), Dr. Rudy Bowen, a professor of Psychiatry at the College of Medicine who studies mood and anxiety disorders, feels that for most of us it should simply be referred to as ‘Seasonal Change in Behaviour and Mood.’
“We participated in a study a few years ago where we tried to recruit people strictly with SAD – people who became depressed only during the winter months,” Bowen said. “It was very difficult to find people because most people had had low moods at other times of the year, but they sometimes become more exaggerated, and occur more frequently, in the winter months.
“This is a continuum that occurs in the general population where people might feel a little low, and might notice slight changes in their behavior. But in people who have a tendency to depression they can become more depressed in the winter months, and that’s what’s been called SAD.”
The causes of SAD haven’t yet solidly been determined, but some of the leading schools of thought believe it has to do with the lack of available sunlight either affecting our circadian rhythm, or a change in either serotonin of melatonin – two brain chemicals that play a role in regulating mood and sleep patterns.
“When it was first described it was thought to be a condition, but we’ve gone away from this now so it’s really a tendency in the population,” Bowen explained. “A lot of people notice seasonal changes, but people who have a tendency to depression anyway may suffer more, and there are perhaps very few people who get depressed exclusively during the winter months – in the dark months.
“And that does seem to be related to the amount of available light, but it may also be related to the rapidity of change of the seasons.”
For most people suffering from a seasonal mood disorder, the most common treatment is quite effective: phototherapy, or light-based therapy. A lamp that mimics sunlight, and can be used for varying amounts of time in the morning, has been shown to help improve moods during the winter months for those suffering from what Bowen calls a Seasonal Change. The more severe, and physician diagnosed, cases of SAD cases have benefitted from the use of common depression treatments prescribed by a doctor.
When it comes to the distance a person lives from the equator, which determines the amount of daily sunlight they’re exposed to in the winter months, research is divided on whether or not incidences of SAD increase.
“The literature isn’t quite clear yet,” Bowen stressed. “There are some studies that indicate it increases, but then there are studies that show very little change as someone goes further north. And it could be that people adapt, or those that survived well in the north are not as genetically predisposed to SAD.”
In fact, a study published by the Canadian Journal of Psychiatry in 2002 looked at the prevalence of SAD amongst Winnipeggers of wholly-Icelandic descent compared to those with no Icelandic heritage found SAD was “markedly higher in the non-Icelandic population than in the Icelandic population.” 
“The research only started about 20 years ago,” Bowen said regarding the conflicting studies. “20 years is a short time for this information to be gathered.”
And while it is a problem, he doesn’t think it’s one that’s increasing – just that awareness of it is – and that there are other depression-related problems that should be focused on.
“I don’t (think) that we should minimize the matter of SAD,” explained Bowen. “But it shouldn’t be exaggerated either – It does exist, but it isn’t the biggest issue in depression.”
You can read more about depression on the Student Health Services website here.
 Axelsson J, Stefánsson JG, Magnússon A, et al. Seasonal Affective Disorders: Relevance of Icelandic and Icelandic-Canadian Evidence to Etiologic Hypotheses. Can J Psychiatry. 2002;47:153–158.