Dark Days; Dark Mood

Friends of mine just left for two weeks of vacation to someplace closer to the equator where they went to soak up some sunshine. For many of us, we experience a visceral desire to go where it’s warm and sunny during the winter. We often say we want to get out of the cold, but it may be more than that. It may actually be a mental health strategy to ward off a particular kind of depression called Seasonal Affective Disorder.

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What do dark days have to do with dark mood?


Seasonal Affective Disorder. Many factors contribute to increased risk for depression, and the dark days of winter can lead to a form of depression known as Seasonal Affective Disorder (SAD). SAD is a type of depression that comes and goes with the seasons, typically starting in the late fall and early winter and going away during the spring and summer. It has the trappings of major depression, but the episodes are triggered by the season.


How does the season increase risk for depression? In the 1980s, Dr. Norman Rosenthal first described Seasonal Affective Disorder when prompted by his own life experience of moving from South Africa to the United States. Unaccustomed to winter, Dr. Rosenthal observed that his mood and productivity declined during this time of year in his new home. Curious to figure out exactly what it was about winter that increased risk for these depressive symptoms, he pioneered research that was seminal to the development of our understanding of SAD today. We now know that reduced sunlight in winter can cause a drop in serotonin, which can further disrupt your body’s internal clock (circadian rhythm) and lead to symptoms of depressed mood and energy. For some, it becomes severe enough to be recognized as Seasonal Affective Disorder.


Who is at risk? Population data indicate that women are diagnosed with SAD four times more often than men. Risk for SAD also increases as a function of stress, biological predisposition, and other forms of depression. Specifically, having blood relatives with SAD or another form of depression and having major depression or bipolar disorder both increase risk. Seasonality is reported by approximately 10 to 20 percent of people with depression and 15 to 22 percent of those with bipolar disorder.


How common is SAD? In the United States, about 5 percent of adults experience SAD, and it typically lasts about 40 percent of the year. However, depending on exact geographic regions, prevalence of seasonal depression can range from negligible to as much as 10 percent of the population. Individuals who live far north or south of the equator have higher prevalence of SAD, with similar rates across the world based on latitude. Nordic countries tend to have the highest rates of SAD, which is correlated with their low levels of overall sunlight during the winter season. As these statistics show, SAD is more common in the parts of the world that are darker (and colder) in the winter.


Light therapy is a key treatment. A major, natural strategy to mitigate depression is light therapy. Once thought to be a treatment of charlatans, light therapy has actually demonstrated great efficacy. We now know that higher light intensities are more effective. Columbia University doctors, Dr. Michael and Jiuan Su Terman, found that 10,000 lux fixtures are most effective for treating SAD. We also know that light therapy is most effective when delivered first thing in the morning from early fall until spring for 20-60 minutes of exposure. In Scandinavian countries, people go to light rooms for light therapy, a practice that is still in need of more data to know whether it is effective in reducing depression.


For those of us in the northern hemisphere, as we make our way through the winter months, we have a few options: spending time outdoors on sunny days, buying a therapy (“happy”) lamp, or taking off to a sandy beach closer to the equator – guess it all depends on time and budget! One way or another, there are things we can all do to keep our mood and energy high during these darker days. And if these natural strategies are not sufficient, additional treatments are available.

Kathleen M. Pike, PhD

Kathleen M. Pike, PhD is Professor of Psychology and Director of the Global Mental Health WHO Collaborating Centre at Columbia University
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