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   Seasonal depression 'caused by increased levels of serotonin transporter   
   protein'   
      
   Last updated: Sat 25 Oct 2014 at 12am PST   
   Depression Mental Health Neurology / Neuroscience Psychology / Psychiatry add   
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   Winter: we have all had those moments when we would rather stay in bed than   
   head out into the cold, dark day. But for those with seasonal affective   
   disorder, winter can trigger a severe form of depression. In a new study,   
   researchers claim to have    
   identified what causes the condition.   
   Unhappy lady looking out the window   
   Researchers say seasonal affective disorder, or seasonal depression, is caused   
   by increased levels of the serotonin transporter (SERT) protein in winter   
   months.   
   Lead researcher Brenda McMahon and her colleagues, from the University of   
   Copenhagen in Denmark, recently presented their findings at the European   
   College of Neuropsychopharmacology (ECNP) Congress in Berlin, Germany.   
      
   Seasonal affective disorder (SAD) is a form of depression that tends to occur   
   at the same time each year, from autumn through winter. SAD affects around   
   500,000 people in the US, while 10-20% of Americans suffer from the "winter   
   blues" - a milder form of    
   seasonal depression.   
      
   Symptoms of SAD are similar to those of clinical depression and include   
   anxiety, sadness, irritability, social withdrawal, lack of concentration and   
   fatigue.   
      
   The exact cause of SAD is unclear, but past studies have indicated that it is   
   triggered by a decline in sunlight in autumn and winter months. Researchers   
   have hypothesized that the reduced exposure to light can cause imbalances of   
   brain chemicals called    
   neurotransmitters, which affect mood.   
      
   In this latest study, the team builds on this theory and claims they have   
   confirmed the biochemical cause of SAD.   
      
   Discovering 'the dial the brain turns up' to adjust to changing seasons   
   To reach their findings, McMahon and her team used position emission   
   tomography (PET) to scan the brains of 11 people with SAD and 23 people   
   without the disorder.   
      
   In particular, they assessed participants' levels of the serotonin transporter   
   (SERT) protein in both winter and summer months. SERT is responsible for the   
   travel of serotonin - a neurotransmitter known to regulate mood.   
      
   Results of the analysis revealed that in winter, SERT levels in participants   
   with SAD were 5% higher than in summer, while participants without the   
   disorder showed no change in SERT levels. The higher levels of serotonin in   
   the winter indicate a greater    
   removal of serotonin from the brain, which can lead to depressive symptoms.   
      
   "SERT carries serotonin back into the nerve cells where it is not active, so   
   the higher the SERT activity, the lower the activity of serotonin," explains   
   McMahon. "Sunlight keeps this setting naturally low, but when the nights grow   
   longer during the    
   autumn, the SERT levels increase, resulting in diminishing active serotonin   
   levels."   
      
   "Many individuals are not really affected by SAD," she continues, "and we have   
   found that these people don't have this increase in SERT activity, so their   
   active serotonin levels remain high throughout the winter."   
      
   McMahon says she believes the team has "found the dial the brain turns up when   
   it has to adjust serotonin to the changing seasons."   
      
   Commenting on these findings, Prof. Siegfried Kasper, of the ECNP, says:   
      
   "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. It seems to offer confirmation that SERT is associated with SAD."   
      
   Last year, Medical News Today published a feature investigating the signs and   
   symptoms of SAD and looking at the treatments available for the condition.   
      
   In this feature, Beth Murphy, head of information at Mind - a UK mental health   
   organization - told us:   
      
   "Talking treatments, such as counseling, psychotherapy or cognitive behavior   
   therapy (CBT) can be extremely useful in helping people to cope with symptoms.   
   Antidepressants may be prescribed for people with severe SAD and can be   
   combined with light    
   therapy for maximum effect."   
      
   More recently, MNT reported on a study suggesting that birth season may   
   influence the risk of later-life mood disorders.   
      
   Written by Honor Whiteman   
      
   Copyright: Medical News Today   
      
   ReferencesAdditional informationCitations   
   European College of Neuropsychopharmacology news release, accessed 21 October   
   2014 via AlphaGalileo.   
      
   Additional source: Cleveland Clinic, seasonal depression, accessed 21 October   
   2014.   
      
      
   http://www.medicalnewstoday.com/articles/284195.php?tw   
      
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