According to psychiatrists in Britain hot weather increases the risk of suicide.
A new study by researchers at the Institute of Psychiatry, in London, has found that of more than 50,000 suicide cases in England and Wales, between 1993 and 2003, when the average daily temperature exceeds 18C (64F) there is a rise in the number of people who kill themselves.
The researchers say they found a 3.8% increase in suicide rates for every 1C rise in average temperature above 18C.
They also found a 1C rise in temperature led to a 5% increase in violent suicide, such as shootings or hangings.
The research has revealed an overall suicide rate increase of 46.9% during the 1995 heat wave, which they say may be linked to psychological, biological or social factors.
The psychiatrists suggest that hot weather can affect the amount of mood controlling chemicals in the brain, and affect people's temperaments, making them more irritable, aggressive and impulsive.
They also suggest that the increase in the amount of alcohol consumed in summer may make people more uninhibited and more likely to attempt suicide.
But the report concludes that psychological factors, particularly the effect of hot weather on people's temperament, are the most likely causes for the increased number of suicides.
The study examined the link between daily temperature and daily suicide rates in England and Wales, between January 1993 and December 2003, over which time there were 53,623 incidents - an average of 13.3 a day; during the 11-year research period, the average temperature was more than 18C on 222 days.
The largest number of suicides took place on Mondays, with numbers declining as the week wore on and three-quarters of all suicides were by men with this proportion remaining constant over the study period.
But the researchers say 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 counselling service the Samaritans says more calls about suicide are received in spring than summer, but the new year remains the peak time, as people struggled with post-Christmas debts and stress.
The study is published in the British Journal of Psychiatry.