A new study suggests that the existence of seasonal depression may be myth, CBS News reports.
Seasonal depression is defined as a mood disorder linked to reduced sunlight in the winter months. However, this form of depression " is not supported by objective data".
However, the seasonal affective disorder was added to the Diagnostic and Statistical Manual of Mental Disorders (DSM) -- the bible of psychological diagnosis -- in 1987.
The new report was published Jan. 20 in Clinical Psychological Science.
Study lead researcher Steven LoBello , a professor of psychology at Auburn University at Montgomery, Ala, said that depression comes and goes but, "it doesn't mean that seasonal changes have caused the depression,".
For the study, LoBello and colleagues used data from a telephone survey of more than 34,000 U.S. adults.
LoBello noted that the study found no evidence that symptoms of depression were season-related.
According to NHS, the researchers concluded that, "Depression was unrelated to latitude, season, or sunlight. Results do not support the validity of a seasonal modifier in major depression.
"The idea of seasonal depression may be strongly rooted in folk psychology, but it is not supported by objective data. Consideration should be given to discontinuing seasonal variation as a diagnostic modifier of major depression."
He said, "If this seasonal pattern of depression occurs at all, it may be fairly rare."
Dr. Matthew Lorber, acting director of child and adolescent psychiatry at Lenox Hill Hospital in New York City, who was not involved in the study, also said that seasonal affective disorder may not be a "legitimate diagnosis."
Lorber said that it was advantageous for big drug companies to have SAD recognized as a standard diagnosis.
"It then allowed them to market to a new population to use their medications. That was a motivating factor in creating this disorder," said Lorber.
Kelly Rohan, an associate professor of psychology at the University of Vermont, has also done research on seasonal depression and found "no season differences in reports of depressive symptoms."
"I certainly did not argue that this means SAD does not exist," she said. "However, only a minority of depression cases are actually SAD."
