Heat not a factor in spring-summer suicide peak

NEW YORK (Reuters Health) - Researchers analyzing more than a century of data have found no evidence that people are more likely to commit suicide in spring and summer due to the hotter weather.

In fact, the researchers found the strongest association between temperature and suicide frequency in the winter, with suicides occurring more often on warmer days. The peak generally involved people who had killed themselves outdoors.

"It seems that outdoor suicides depend on agreeable temperatures and, in some suicide methods, this issue is particularly relevant in winter," Dr. Vladeta Ajdacic-Gross of the University of Switzerland in Zurich and colleagues write.

While suicides are known to occur more frequently in spring and summer than in winter, the investigators note, decades of research have been unable to show whether or not seasonal factors like temperature, sunlight or precipitation might somehow be responsible.

To test the hypothesis that temperature and other climatic factors play a role, Ajdacic-Gross and colleagues looked at data on suicide and weather conditions in Switzerland from 1881 to 2000.

The researchers found that, overall, suicide frequency rose with temperature, but it was not associated with daily hours of sunshine or amount of precipitation.

But more detailed analysis found the strongest relationship between temperature and suicide frequency in the winter months. The association between temperature and suicide was strongest for jumping from high places and being run over by a train.

Based on the findings, the researchers conclude, while climatic variables like temperature may play an indirect role in suicide frequency, they cannot explain overall seasonal patterns.

SOURCE: American Journal of Epidemiology, March 1, 2007.