Seattle is often considered the suicide capital of the United States. Psychology experts often attribute the city’s consistently high rates of suicide attempts to its dreary weather. It makes sense that rain and clouds are usually blamed for depression, but if bad weather can play a role in suicidal tendencies, why do suicide rates seem to increase during springtime? A recent study conducted at the Medical University of Vienna in Austria has revealed that sunshine and clear skies are a motivating factor in many suicides.

Lead researcher Dr. Matthäus Willeit and his colleagues gathered all data on confirmed suicides in Austria between Jan. 1, 1970 and May 6, 2010. Data from 69,462 suicides was compared to the average duration of sunshine per day via 87 meteorological stations. The research team also analyzed methods of suicide, whether they were violent suicide methods (hanging, drowning, or shooting), or nonviolent suicide methods (poisoning).

Results showed an apparent link between hours of sunshine in a day and the number of suicides. Sunshine on the day of or up to 10 days prior to a suicide was common throughout the study. On the other hand, there was no link “between the number of suicides and daily hours of sunshine for the 14 to 60 days prior to the suicide event,” the authors stated. Findings held up for both violent suicide methods and nonviolent suicide methods.

Austrian researchers provided possible explanations as to why sunny weather seems to increase the risk of a suicide. One theory involves the relationship between sun exposure and the neurotransmitter serotonin, which plays a major role in emotions and mood swings. So-called bright light therapy for people suffering from depression tends to improve drive and motivation before mood. “If you have enhanced energy and motivation and drive but your mood is still very depressed, that might favor a state where you are at greater risk for suicide,” Willeit added.

According to the Centers for Disease Control and Prevention, 39,518 suicides were reported in 2011, making it the 10th leading cause of death in the United States. While the holiday season is commonly associated with a spike in suicide rates, CDC data has shown that the month of December is when the least amount of suicides occur. The same data sets also confirm that springtime is when the most suicides occur out of all four seasons.

Source: Vyssoki B, Kapusta N, Prschak-Rieder N, Dorffner G, Willeit M. Direct Effect of Sunshine on Suicide. JAMA Psychiatry. 2014.