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Long periods of darkness have traditionally been associated with depression.

But now a study says that high levels of sunshine - at least in the short term -  are linked to higher suicide rates.

While a cause is not known, it's thought that the light could interact with the mood-altering neurotransmitter serotonin, which affects the mood of both humans and animals.

Researchers from the University of Vienna have found a correlation between sunshine hours and suicide rates. They found suicides increased when a day was particularly sunny (stock image shown). However if the preceding 14 to 60 days were sunny the rate dropped

The research from the University of Vienna, reported by LiveScience, appears in the journal JAMA Psychiatry.

They looked at sunshine hours and suicide rates in Austria from 1 January 1970 to 6 May 2010.

Sunshine hours were calculated from 86 meteorological stations. The study looked at more than 69,000 suicides over the 40 years.

They found that, on each day studied, sunshine hours and the number of suicides were highly correlated.

'Sunshine on the day of suicide and up to 10 days prior to suicide seems to facilitate suicide,' the researchers write.

However, prolonged sunshine 14 to 60 days prior to a given day was found to reduce the rate.

The researchers also found a stronger link between suicide rates among women and sunshine hours.

For men, on the other hand, the link between lower suicide rates after prolonged sunshine was stronger.

The exact reason for the results of the study is not known, but previous studies have shown that light interacts with serotonin, a neurotransmitter in humans and animals that affects mood.

This means exposure to sunlight could alter serotonin levels and lead to erratic behaviour and emotions.

The researchers also found a stronger link between suicide rates among women and sunshine hours. For men, on the other hand, the link between lower suicide rates after prolonged sunshine was stronger.Sunlight is thought to alter levels of serotonin, which is known to affect peoples' moods (stock image shown)