Britain may finally be basking in summer sunshine after the wettest July in more than 200 years, but psychiatrists have still managed to dampen the country's spirits. Hot weather increases the risk of suicide, according to research published today.
A study of more than 50,000 suicide cases in England and Wales, between 1993 and 2003, finds that once the average daily temperature exceeds 18C (64F) there is a rise in the number of people who kill themselves.
There is a 3.8% increase in suicide rates for 1C rise in average temperature above 18C, according to researchers at the Institute of Psychiatry, in London.
There is an even stronger link between hot weather and violent suicide, such as shootings or hangings, with a 1C rise leading to a 5% increase in such deaths.
The overall suicide rate increased by 46.9% during the 1995 heatwave, the research reveals.
The researchers say the rise in the suicide rate may be linked to psychological, biological or social factors.
They suggest hot weather can affect the amount of mood controlling chemicals in the brain, or even that the increase in the amount of alcohol consumed in summer may make people more uninhibited - and 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.
One of the researchers, Lisa Page, says: "We felt overall that the most likely explanation was probably a psychological one where for some people you have an unusually high degree of irritability, aggression and impulsivity."
The study, published in the British Journal of Psychiatry, examines 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.
But the research suggests that if there is more than one heatwave in a single year the suicide rate does not increase significantly, possibly because people are more used to the hot weather.
A spokesman for the Institute of Psychiatry said: "The surprising finding that suicides increased during the 1995 heatwave, but not during the 2003 heatwave, may be explained by the fact that there were two periods of very hot weather in 2003, in mid-July and in August.
"The later heatwave in August may have resulted in fewer deaths through adaptation to higher temperatures among vulnerable people."
A spokeswoman for the counselling service the Samaritans, said its helpline received more calls about suicide in spring than summer, although the new year remained the peak time, as people struggled with post-Christmas debts and stress.
The spokeswoman said: "Springtime tends to be busier than summer - apparently because that's when a lot more people tend to be coupled off and others feel more isolated."