Seasonal Affective Disorder (SAD) – Part I

What is SAD?

SAD is a type of depression that occurs primarily during winter months in colder climates where these geographies experience decreases in seasonal sunlight. While it is possible to be afflicted with SAD during spring and summer months, we will be focusing our post on winter-onset of SAD. Our bodies responds physiologically to changes in season and sunlight by altering chemical production that regulate core functions such as sleep and appetite — it is these changes that have been hypothesized as one of the key factors in causing SAD.

According to Environment Canada, Toronto experiences an average of 2,066 sunshine hours, or 45% of daylight hours, varying between a low of 28% in December (29% in January) to 60% in July.  That means on average, Toronto receives less than 4 hours of sunlight a day in December and January compared to over 7 hours of daily sunlight in July – staggering!  Given the severe swing in sunlight hours (the same can be said for temperatures levels too), it’s easy to see how Torontonians are more susceptible to more than just the occasional bout of the winter blues.


Winter-onset SAD symptoms can include:

  • Depression
  • Hopelessness
  • Anxiety
  • Loss of energy
  • Heavy, “leaden” feeling in the arms or legs
  • Social withdrawal
  • Oversleeping
  • Loss of interest in activities you once enjoyed
  • Appetite changes, especially a craving for foods high in carbohydrates
  • Weight gain
  • Difficulty concentrating


While there have not been conclusive links to causes, evidence has strongly suggested that other mental conditions, genetics, age, sex and your body’s biological balance play an important role in developing the condition.  More specifically, your body responds to decreases in temperature and sunlight by disrupting serotonin (a neurotransmitter that regulates mood, sleep and appetite) and melatonin (an important hormone that controls your sleep-wake-cycle) production.  While these chemicals are naturally produced by the body throughout the year, it is the imbalance of these chemicals between seasons that may cause the depression.

Next week, we will focus on treatment and preventative remedies.  If you suspect that you are experiencing more than just the “winter blues” and that your current symptoms are having a detrimental impact on your daily life, please contact your primary healthcare provider immediately.