Potential Cause of Seasonal Affective Disorder Revealed

sad-girl-under-gray-skiesAs the warm weather and long days of summer steadily give way to the long, cold nights of fall and winter, many people find themselves falling into depression. About 5% of the population experiences seasonal affective disorder (SAD), a type of depression that coincides with seasonal changes. Mental health professionals have long struggled to understand the condition, which is most common during the winter months when UV light levels are low. Symptoms can occur at any time though, and a small number of people experience SAD during the summer. According to a study presented this month at the European College of Neuropsychopharmacology, researchers now have a stronger understanding of what causes this mysterious condition.

What Causes Seasonal Affective Disorder?

Researchers worked with a small study sample, evaluating 11 people who had SAD and 23 people without it. Using PET scans, researchers evaluated the presence of two chemicals: serotonin, a neurotransmitter implicated in depression and mood regulation, and serotonin transporter protein (SERT). SERT transports serotonin to nerve cells, where the neurotransmitter is inactive.

Researchers found that people without SAD actually have lower levels of SERT during the winter, but higher levels during the summer. Because SERT carries serotonin to nerve cells where it remains inactive, more SERT in the brain suggests the presence of lower serotonin. Researchers concluded, then, that SAD is a product of insufficient serotonin levels, and that the behavior of SERT causes these low serotonin levels.

Doctors have long prescribed UV light therapy to treat people experiencing SAD during the winter. The authors of this study suggest that light therapy might act on serotonin, and have already been discussing plans for a study addressing the effects of light therapy.

Understanding Seasonal Affective Disorder

Seasonal affective disorder is more than just the winter doldrums. People with SAD may feel persistently hopeless, sad, and exhausted. Symptoms of SAD include:

If you think you might have SAD, therapy can help. GoodTherapy.org can help you find a therapist using this link.


  1. Lincoff, N. (2014, October 28). Why so SAD? Researchers get to the bottom of seasonal affective disorder. Retrieved from http://www.healthline.com/health-news/researchers-get-to-the-bottom-of-seasonal-affective-disorder-102814#2
  2. Seasonal affective disorder (SAD). (2014, September 12). Retrieved from http://www.mayoclinic.org/diseases-conditions/seasonal-affective-disorder/basics/symptoms/con-20021047

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  • Caroline


    October 30th, 2014 at 2:47 PM

    Do you think that there is a way that mood could be stimulated pharmaceutically via serotonin? This seems like it would be a good option for those who may not respond too well to other treatments.

  • Gail Rosen, LCSW

    Gail Rosen, LCSW

    October 31st, 2014 at 10:38 PM

    Many people take (or increase their) antidepressants during this period of time. SSRIs are commonly used to treat Seasonal Affect Disorder.

  • margie


    October 31st, 2014 at 11:29 AM

    My mother always had this sadness about her every year around the same time in the winter and I always thought that maybe there were some bad memories for her that centered around this time of year, but the more I have read the more that I think that she probably struggled with SAD all of her life but we just didn’t know enough then to put a name to what she was experiencing and certainly not enough to even know what to do to make it better for her.

  • Kori


    October 31st, 2014 at 2:14 PM

    All of those symptoms above sound like depression so how does one differentiate?

  • Gail Rosen, LCSW

    Gail Rosen, LCSW

    October 31st, 2014 at 10:34 PM

    It is depression. However it is depression caused by the change in season affecting our circadian rhythm and bio-chemicals. Many people take (or increase their) antidepressants over this period of time to help them.

  • Cindy


    November 28th, 2014 at 4:44 PM

    What makes SAD different from depression is that SAD only occurs “seasonally”, such as in the fall and winter which also coinsides with the holidays.

  • Doris


    November 1st, 2014 at 4:22 PM

    A plane ticket to a sunny climate and a prescription for Vitamin D capsules can be very beneficial..

  • Edy


    November 2nd, 2014 at 12:34 PM

    In May 1999 my oldest son was killed. At the time I was on Prozac to see if it would change my moody eating habits. I went off the prozac as it seemed to be stifeling my abilty to greive. I didn’t react until about Thanksgiving of that year. Now I wonder if it was going off the prozac,the seasonal depression or the fact that it was holidays and part of the family was missing. Or perhaps it was all 3 but I still get weepier in Novemebr than I do in MAy 15 years later. Not on meds now. I don’t know what is to feel normal. Wish I knew so I knew if anything was working.

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