Depressive symptom levels do not vary from season to season in most people, says the Association for Psychological Science. These findings were published online in the journal Clinical Psychological Science on January 19, 2016.
The research was based on large scale survey of U.S. adults that investigated seasonal affective disorder (SAD). A SAD diagnosis is defined as meeting the criteria for major depression and recurring depressive episodes that coincide with certain times of the year. Most patients report that their symptoms increase in the fall and winter, and decrease in spring and summer.
“In conversations with colleagues, the belief in the association of seasonal changes with depression is more or less taken as a given and the same belief is widespread in our culture,” says Steven LoBello, a professor of psychology at Auburn University at Montgomery and senior author on the study. “We analyzed the data from many angles and found that the prevalence of depression is very stable across different latitudes, seasons of the year, and sunlight exposures.”
Reseachers say that more recent studies are challenging earlier SAD research and how SAD is identified. Patients who are diagnosed with this condition are usually asked to recall past depressive episodes during one year or more. In addition, the established criteria for major depression dies not align with criteria used to identify SAD.
Researchers based the study on the 2006 Behavior Risk Surveillance System, an annual phone-based health survey. Data was examined on 34,294 participants ages 18 to 99. They did not find evidence of seasonal differences in a subsample of 1, 754 participants who were classified as having clinical depression.
Participants were asked how many days in the previous two weeks that they had experienced depressive symptoms. Season-related measurements were taken in each participants’ geographical location such as the day of the year, the latitude, and the amount of sunlight exposure. Participants did not have noticeably higher levels of depressive symptoms than those who responded at other times of the year.
“The findings cast doubt on major depression with seasonal variation as a legitimate psychiatric disorder,” the researchers concluded. “Being depressed during winter is not evidence that one is depressed because of winter.” They acknowledged that it is possible that SAD does exist, but only for a small percentage 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 said. “Pursuit of treatments based on false causes is unlikely to lead to rapid and durable recoveries.”