Seasonal affective disorder (SAD), a “seasonal pattern” modifier for depression diagnoses, was officially added to the Diagnostic and Statistical Manual of Mental Disorders (DSM) in 1987. Recently, researchers investigated whether they could find evidence for seasonal variation in depressive symptoms using data from a large-scale survey of 34,294 US adults ranging in age from 18 to 99 years. Depressive symptoms were measured using the PHQ-8, which asked participants how many days in the previous two weeks they had experienced given symptoms of depression. Using geographic location for each participant, the researchers also obtained season-related measures, including the actual day of the year, the latitude, and the amount of sunlight exposure. The results showed no evidence that symptoms of depression were associated with any of the season- related measures. That is, people who responded to the survey in the winter months, or at times of lower sunlight exposure, did not have noticeably higher levels of depressive symptoms than those who responded to the survey at other times. And the researchers did not find any evidence for seasonal differences in symptoms when they specifically looked at the subsample of 1,754 participants who scored within the range for clinical depression. Taken together, the findings suggest that seasonal depression is not the prevalent disorder that it’s commonly thought to be. More studies into the validity of SAD must be performed before final conclusions can be drawn.
Sources: Association for Psychological Science. https://www.psychologicalscience.org; Traffanstedt MK, Mehta S, LoBello SG. Major depression with seasonal variation: Is it a valid construct? Clinical Psychological Science. 2016;4(5):825–834.