Rainy and cloudy days are often associated with gloom but it appears that short streaks of sunny days are actually tied with tendencies for suicide, findings of a new research suggest.

In the new study published in the JAMA Psychiatry on Sept. 10, Matthäus Willeit, from the Department of Psychiatry and Psychotherapy of the Medical University of Vienna in Austria, and colleagues analyzed over 69,000 confirmed suicide cases that occurred in Austria between January 1970 and May 2010 to determine if sunlight is associated with suicide rates. The researchers also used data from meteorological stations to determine the daily duration of sunlight during the period that spanned 40 years.

The researchers found that during ten days or less of sunshine, suicide rates tend to increase but two weeks to two months of sunshine were tied to lower suicide rates.

"Our data support the hypothesis that sunshine on the day of suicide and up to 10 days prior to suicide may facilitate suicide," the researchers wrote. "More daily sunshine 14 to 60 days previously is associated with low rates of suicide. Our study also suggests that sunshine during this period may protect against suicide."

The researchers have several theories on why sunny weather appears to boost people's tendencies to commit a suicide. The most plausible of these involves serotonin, a neurotransmitter that plays a role in emotions and impulsivity.

Exposure to sunlight is correlated to serotonin levels in the brain and thus, shorter sunny days could affect the levels of serotonin and cause erratic behaviors and emotions. Some scientists theorize that the effect of sunlight in some depressed people may be similar to that of an antidepressant. It may improve their motivation first and their depression symptoms later. Sunny days that last longer, however, appear to provide a protective effect as they seem to sustain elevated mood for a longer period.

"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 said.

The researchers said they plan to conduct further research on the association between light and serotonin and pointed out that while they have found a link between sunny days and suicide, the effect is actually very small. Experts said that people should not avoid the sun simply because of the study's findings.

Figures from the Centers for Disease Control and Prevention show that there were over 39,000 deaths due to suicide in 2011.

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