Seasonal affective disorder is a mood disorder which occurs in winter and is linked to a lack of energy, fatigue, overeating and a tendency to sleep longer as well as depressed mood. Researchers at the University of Toronto in Canada looked into the links between the seasons and the levels of a serotonin transporter in the brain. The serotonin transporter 'mops up' serotonin in the brain leading to reduced levels of serotonin, the brain's 'feel-good' chemical so the higher the levels of serotonin transporter the higher the risk of depression. The researchers found that the serotonin transporter was significantly more active in the autumn and winter and believe that light may have a direct effect on the activity of the protein. The study was based on brain scans of 88 volunteers carried out between 1999 and 2003.
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