Brain PET: Seasonal Affective Disorder is caused by higher serotonin transport

Seasonal Affective Disorder (SAD) appears to be brought on in the darker months of the year due to a drop in serotonin, which is mediated by the serotonin transporter protein (SERT), according to a longitudinal PET study presented Monday in Berlin during the Congress of the European College of Neuropsychopharmacology.

The biology of SAD has long been pondered, but now researchers from the University of Copenhagen report that as darkness falls, so does SERT, which hampers serotonin availability and the feelings of happiness it brings.

"SERT fluctuations associated with SAD have been seen in previous studies, but this is the first study to follow patients through summer and winter comparisons,” commented Siegfried Kasper, MD, professor of psychiatry and chairman of the department of psychiatry and psychotherapy at the Medical University of Vienna, Austria, in an official statement. “It seems to offer confirmation that SERT is associated with SAD."

For this study, researchers imaged 11 volunteers affected by SAD and 23 healthy controls in both winter and summer months to gauge any potential difference. Results of the study showed that SAD patients had 5 percent higher levels of SERT in the winter compared to their happier counterparts, who showed no significant change.

In the summer, natural sunlight helps to keep SERT levels low. Scientists are still grappling with how to use this knowledge to help treat those who come down with SAD once the leaves begin to fall. The ECNP reports that in Northern European lattitudes, about one in every six people is affected by the disorder.