New research suggests seasonal affective disorder does not exist
But SAD, or seasonal affective disorder, long blamed for causing bouts of clinical depression does not actually exist, a scientific study claimed yesterday.
The conclusion was derived from a large scale survey of US adults that found no evidence that levels of depressive symptoms vary from season to season.
Professor of psychology Steven LoBello at Auburn University at Montgomery said: "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.
"We analysed 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."
Scientist analysed data from people experiencing depression in different seasons
Prevalence of depression is stable across different seasons
SAD was first officially recognised as a depression disorder in 1987 and those afflicted not only have to meet the diagnostic criteria for major depression but also experience recurring depressive episodes that coincide with specific seasons.
Most patients report an increase of symptoms in autumn and winter and a decrease in symptoms in spring and summer.
But SAD has been challenged so the study published in in Clinical Psychological Science, a journal of the Association for Psychological Science, looked for evidence the seasons affect depression.
It looked at data from 34,294 participants aged 18 to 99 in the phone-based health survey conducted annually as part of the 2006 Behavioural Risk Factor Surveillance System (BRFSS).
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 researchers then compared their geographic location and how seasons affect that place.
It found 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.
Researchers say there is no evidence to support people are depressed because of winter
Prof LoBello added: "The findings cast doubt on major depression with seasonal variation as a legitimate psychiatric disorder."
Depression is by definition an episodic disorder and people may well experience depressive episodes in the autumn and winter months but "being depressed during winter is not evidence that one is depressed because of winter."
However the study concedes because of the small sample, it's possible that major depression with seasonal variation does exist but only for a very small proportion of the population.
People pursuing treatments based on false causes are unlikely to have a lasting recovery
But even so, it is not as widespread as once thought.
Prof LoBello said: "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.
"Pursuit of treatments based on false causes is unlikely to lead to rapid and durable recoveries."