According to a large-scale survey of U.S. adults, recently published in the journal Clinical Psychological Science, the severity of depressive symptoms have no statistically significant relation to seasonal change.
Despite the widespread notion that lack of sunshine can bring on the blues, the research team behind the study found the prevalence of depression to be remarkably stable across different latitudes, seasons of the year, and sunlight exposures. Could this mean that Seasonal Affective Disorder (or SAD) does not exist?
Recognized by the DSM for the first time in 1987, SAD is diagnosed by first evaluating a patient’s symptoms to see if they meet the criteria for major depression, and then finding out whether they follow a seasonal pattern.
With new analyses calling the quality of past research on SAD into question, however, the research team decided to conduct a large-scale independent survey.
To this end, they analysed the data of 34,294 participants (aged 18 to 99) of the 2006 Behavioural Risk Factor Surveillance System (BRFSS), a phone-based health survey conducted every year.
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. The PHQ-8 has been validated in previous research as a reliable measure of depression in line with DSM diagnostic criteria.
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 relation between depression and any of these variables. While people do get depressed during winter, noted Steven LoBello, Professor of Psychology at Auburn University at Montgomery and senior author on the study, it does not mean it happens because of winter.
One caveat worth mentioning, however, is that low base rate conditions like depression are difficult to detect in large-scale studies, meaning there is a slight probability that SAD exists, although only for a tiny fraction of the population.
“Mental health professionals who treat people with depression should be concerned about their own and their patients’ accurate conceptions about the possible causes of depression,” LoBello says. “Pursuit of treatments based on false causes is unlikely to lead to rapid and durable recoveries.”