Hot weather affects mood-controlling chemicals in the brain and may trigger suicidal tendencies, a study by British researchers suggests.
Sweltering weather makes people more irritable, aggressive and impulsive, they say.
Psychiatrists at the Institute of Psychiatry in London examined the link between daily temperature and daily suicide rates in England and Wales, between January 1993 and December 2003.
There were 53,623 incidents - an average of 13.3 a day. During the 11-year research period, the average temperature was higher than 18 degrees Celsius on 222 days.
The researchers say they found a 3.8 per cent increase in suicide rates for every one degree Celsius rise in average temperature above 18 degrees Celsius.
They also found a one-degree rise in temperature led to a five per cent increase in violent suicides, such as shootings or hangings, reported health portal News Medical.
The research has revealed an overall suicide rate increase of 46.9 per cent during the 1995 heat wave, which they say may be linked to psychological, biological or social factors.
The largest number of suicides took place on Mondays, with numbers declining as the week wore on. Three-quarters of all suicides were by men with this proportion remaining constant over the study period.
However more than one heat wave in a single year does not significantly increase the suicide rate, possibly because people become adapted to the hot weather, the study published in the British Journal of Psychiatry said.