In a new research published in Clinical Psychological Science, which is a journal under the Association for Psychological Science, a large scale survey involving US adults shows no evidence that the symptoms of depression vary between seasons.
These results are quite contradictory with the notion that depression occurs seasonally. Steven LoBello, professor of psychology at Auburn University at Montgomery and also a senior author of the study, says that when he talks to colleagues, thinking that the changing of seasons is associated with depression is more-or-less a given fact and the same way of thinking is also widespread in our culture.
We analyzed data from many angles and found out that the prevalence of depression is very stable across different latitudes, seasons of the year, and sunlight exposures, says LoBello.
Seasonal Affective Disorder
Seasonal affective disorder (SAD), is a seasonal pattern modifier for diagnosing depression and was officially included in 1987 in the Diagnostic and Statistical Manual of Mental Disorders (DSM). In order to be diagnosed as clinically depressed with seasonal variation, patients must be assessed using criteria for major depression, as well as recurring episodes in specific seasons. For most patients, symptoms increase during fall and winter, and decrease when spring and summer comes.
Recent studies, however, have challenged the idea of SAD, including the fact that patients are usually asked to recall episodes over the course of the previous year or even earlier than that. Another point is that the criteria that is used to diagnose SAD do not really line up with the criteria that is being used to diagnose major depression.
The researchers investigated data acquired last 2006 as part of the Behavioral Risk Factor Surveillance System (BRFSS), which is a phone-based survey that is done every year. They examined data from a total of 34,294 people who were aged 18-99. The symptoms that were experienced were measured using PHQ-8, which basically assesses how many times patients experienced depressive symptoms in the past two weeks. This method has been established as a reliable method for the diagnosis of depression as recommended by DSM diagnostic criteria.
Analysis of the data showed that there was no correlation between symptoms of depression and season-related measures. To be more specific, people who answered the surveys during the winter months, or times of lower light exposure, did not have significantly higher depressive symptoms, as compared to those who answered the survey at other times of the year.
Looking at the subsample of 1,754 participants that were also diagnosed to be clinically depressed, the researchers also found the same conclusion: there were still no seasonal differences in symptoms.Because of this, the researchers have concluded that it is doubtful that major depression with seasonal variation is actually a legitimate psychiatric disorder.
Depression is known to be an episodic disorder, and it people would as well experience depressive symptoms in the colder months. The researchers however say that being depressed during winter is not evidence that one is depressed because of winter.
Putting all of these together, seasonal depression might not be the prevalent disorder that it's previously thought to be.