US researchers found that neither time of year nor weather conditions influenced depressive symptoms. (Agencies)
However, lead author David Kerr of Oregon State University said this study does not negate the existence of clinically diagnosed seasonal affective disorder, also known as 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. Though 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.
Kerr and his colleagues 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 behaviour, 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, 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," Shaman said.
US researchers found that neither time of year nor weather conditions influenced depressive symptoms.