The interaction of light with brain serotonin systems could possibly influence serotonin-related behaviours such as mood and impulsiveness. This can, in turn, affect the suicidal behaviour in an individual.
The authors examined the relationship between suicide and the duration of sunshine after mathematically removing seasonal variations in sunshine and suicide numbers. They analyzed data on 69,462 officially confirmed suicides in Austria between January 1970 and May 2010. Hours of sunshine per day were calculated from 86 representative meteorological stations.
There was a positive correlation between the number of suicides and hours of daily sunshine on the day of the suicide and up to 10 days before that seemed to facilitate suicide, while sunshine 14 to 60 days prior appeared to have a negative correlation and was associated with reduced suicides. The correlation between daily sunshine hours and suicide rates was seen largely among women, while negative correlations between the two were mainly found among men.
"Owing to the correlative nature of the data, it is impossible to directly attribute the increase in suicide to sunshine during the 10 days prior to the suicide event. ... Further research is warranted to determine which patients with severe episodes of depression are more susceptible to the suicide-triggering effects of sunshine."