Seasonal affective disorder (SAD) is a form of depression that most commonly arises with changes in exposure to daylight, which can occur in both the summer and winter months. However, the winter form of SAD is more commonly seen.
“SAD is defined as a variation in mood when there is a change in season. It most commonly occurs in the Northern Hemisphere during the winter,” says John P. Docherty, MD, of Weill Cornell Medical College in New York City. “The onset of this syndrome occurs in the winter months when the days are shorter and there is less exposure to sunlight,”
Approximately 500,000 Americans suffer from winter SAD, with approximately 10 to 20% suffering from a milder form. The condition most commonly occurs in young adults and affects women to a greater extent than men.1
According to Meir Kryger, MD, of Yale School of Medicine in New Haven, Connecticut, SAD is commonly referred to as “winter depression” or “winter blues.”
“In the Northern Hemisphere, the condition is much more common the further north one lives and the less sunlight one is exposed to. SAD is common in Seattle and Alaska. Being further north without a lot sunshine is a recipe for SAD,” Kryger says.
Symptoms of Seasonal Affective Disorder
Symptoms of SAD include but are not limited to sadness, anxiety, irritability, loss of interest in usual activities, withdrawal from social activities, inability to concentrate, lack of energy, and weight gain.2
“When there is not a lot of sunlight during these short days, some people start to develop symptoms similar to clinical major depression, such as feeling pervasively sad and sleepy. They may [also] start to put on weight,” says Kryger.
While the symptoms of SAD overlap with major depressive disorder (MDD), seasonality is the main distinguishing feature of SAD.3 “The depressive symptoms may be indistinguishable from MDD, but they usually lift when springtime comes,” he adds.
Comorbidities Tied to a Higher Risk of Seasonal Affective Disorder
Although the exact underlying mechanism of action of SAD remains unclear, risk factors for the condition exist. According to Norman Rosenthal, MD, author of Winter Blues, a guide to understanding and coping with SAD, “There are three fundamental causes of SAD including genetic and biologic tendency, lack of light, and stress. The combination of these three factors creates the perfect storm and the risk of SAD.”
“There is a reported genetic variation that can make you more vulnerable. A photoreceptor (the melanopsin receptor) has a reported variation that is related to a five to six times increased risk for SAD,” Docherty adds. “It doesn’t mean that is the only reason you could get this condition. We have whole pathways through which light transmits its action to suppress melatonin release. Possible aberrations at any one or more than one of those steps might account for the presence of this condition.”