Since the early 1800s , scientists have known about a seemingly paradoxical relationship between the seasons and suicide rates: Suicides soar in the spring, rather than winter.  Even more counterintuitive, perhaps, is that this peak has a reverse correlation with spikes in rates of Seasonal Affective Disorder, or SAD. In the words of the Mayo Clinic , SAD is “a type of depression that occurs at the same time every year...sapping your energy and making you feel moody,” and approximately 5 percent of the population develops SAD during cold months, whereas some one percent develops the condition during warm months.
While this sunny weather-suicide correlation has long been established within the medical community, scientists hadn’t studied it apart from seasonal shifts. In a paper published Wednesday in Journal of the American Medical Association Society Psychiatry (JAMA Psychiatry) , researchers at the Medizinische Universitat Wein , the Medical University of Vienna, argue that sunshine is indeed linked to fatal self-harm, independent of the season.
The researchers studied the Austria's suicide data (date of suicide, gender of the deceased and method, all provided by Statistics Austria) from Jan. 1 1970 to May 6, 2010 alongside meteorological data for the same time period. Of the 69,462 suicides registered in Austria during that 40-year period, they found that days with more suicides tended to be sunnier.
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In addition, the effects of sunlight were not limited to the day of suicide alone; a string of sunny days often ended in tragedy, according to the data in Austria.
Dr. Matthaeus Willeit, a professor at the Medical University of Vienna and the study’s senior author, puts it this way: “The amount of light approximately two weeks before a suicide event is positively correlated with suicide. The more light you have in a certain period, probably short-ranging, the more likely a person who is already at risk to commit suicide.”
The neurobiology of sunlight exposure gives insight into why this is the case. Sunlight exposure is correlated to serotonin levels in the brain; while this neurotransmitter is one of several that generate happiness, it is alsoassociated with impulsivity . So someone already thinking about suicide may be triggered into an impulsive action by exposure to short bursts of sunlight and serotonin.
Conversely, longer-range sunlight increases seem to have a “protective effect” — elevating moods in a way that are sustainable for a longer time period. It’s unclear the connection between these two seeming contradictions, and Willeit says the research team plans on further researching the relationship between light and the serotonin system.
Dr. Norman Rosenthal, author of Winter Blues  and clinical professor of psychiatry at Georgetown University, who was the first to describe SAD in 1984, tells Newsweek that the study is “ a novel analysis of data that is very well collected and well characterized.”
He adds: "It’s really important for people to understand that the physical environment influences peoples’ moods and it doesn’t always do it in an expected way."