We now know that seasonal depression, or seasonal affective disorder, is associated with a lack of light. It also affects nearly one in six people in the Nordic countries, which benefit from very few hours of sunshine in winter. But Danish researchers wanted to know more and decipher the mechanism of this mood disorder. They therefore gave a brain scan (a PET scan) to 11 patients with seasonal depression and 23 healthy patients, in summer and winter.
“These PET scans showed significant differences in serotonin transporter (SERT) levels in summer and winter. We believe we have found how the brain works when it has to adjust serotonin production to changes in seasons, “says Dr Brenda Mc Mahon of the University of Copenhagen (Denmark), lead author of the study.
Patients with seasonal depression had higher levels of serotonin transporter (SERT) than others in winter, which corresponds to a greater elimination of serotonin, the hormone responsible for our sleep-wake rhythm.
While people unaffected by seasonal mood disorder had elevated active serotonin levels all winter long.
The role of serotonin in seasonal depression has already been pointed out in other studies, but this is the first time that researchers have followed patients in both winter and summer. For Dr Mac Mahon, this confirms the interest of light therapy in the treatment of seasonal depression.
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