Seasonal affective disorder’s mood changes are often attributed to a change in circadian rhythm, drops in the neurotransmitter serotonin due to reduced sunlight or a change in melatonin levels that impede sleep.
New research, however, suggests these well-known variables may not influence depression as much as is often believed.
In a study recently published online in the Journal of Affective Disorders, researchers found that neither time of year nor weather conditions influenced depressive symptoms.
Nevertheless, lead author David Kerr of Oregon State University said this study does not negate the existence of clinically diagnosed seasonal affective disorder (SAD), but instead shows that people may be overestimating the impact that seasons have on depression in the general population.
“It is clear from prior research that SAD exists,” Kerr said. “But our research suggests that what we often think of as the winter blues does not affect people nearly as much as we may think.”
Kerr said the majority of studies of seasonal depression ask people to look back on their feelings over time.
“People are really good at remembering certain events and information,” he said. “But, unfortunately, we probably can’t accurately recall the timing of day-to-day emotions and symptoms across decades of our lives. These research methods are a problem.”
So Kerr and his colleagues tried a different approach.
They analyzed data from a sample of 556 community participants in Iowa and 206 people in western Oregon. Participants completed self-report measures of depressive symptoms multiple times over a period of years.
These data were then compared with local weather conditions, including sunlight intensity, during the time participants filled out the reports.
In one study, some 92 percent of Americans reported seasonal changes in mood and behavior, and 27 percent reported such changes were a problem. Yet the study suggests that people may be overestimating the impact of wintery skies.
“We found a very small effect during the winter months, but it was much more modest than would be expected if seasonal depression were as common as many people think it is,” said Columbia University researcher Jeff Shaman, Ph.D., a study co-author and a former OSU faculty member.
“We were surprised. With a sample of nearly 800 people and very precise measures of the weather, we expected to see a larger effect.”
Kerr believes the public may have overestimated the power of the winter blues for a few reasons. These may include awareness of SAD, the high prevalence of depression in general, and a legitimate dislike of winter weather.
“We may not have as much fun, we can feel cooped up and we may be less active in the winter,” Kerr said. “But that’s not the same as long-lasting sadness, hopelessness, and problems with appetite and sleep – real signs of a clinical depression.”
According to Kerr, people who believe they have SAD should get help. He said clinical trials show cognitive behavior therapy, antidepressant medication, and light box therapy all can help relieve both depression and SAD.
“Fortunately, there are many effective treatments for depression, whether or not it is seasonal,” he said. “Cognitive behavior therapy stands out because it has been shown to keep SAD from returning the next year.”
Source: Oregon State University