Each degree above 18C (64.4F) increases risk by almost 4%.
The damp summer may have made us all miserable, but research suggests it is hot weather that poses a far more serious problem for vulnerable people.
A team from London’s Institute of Psychiatry found that suicide rates go up during hot weather.
Analysis of more than 50,000 suicides in England and Wales between 1993 and 2003 showed the suicide rate rose when average daily temperatures topped 18C.
The study appears in the British Journal of Psychiatry.
The researchers found that once the daily average temperature rose above 18C each further degree increase was associated with a rise in suicides of almost 4%.
The rate in the rise of violent suicides was even higher, at 5% per degree rise in temperature.
Aggression and irritability
Researcher Dr Lisa Page said there were a number of possible reasons for the link between hot weather and suicide.
She said: “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.”
She said it was possible that the effect was linked to levels of the mood-controlling chemical serotonin in the brain, which have been shown to dip in the summer months.
Alternatively, the suicide rate may be linked to the tendency to consume higher levels of alcohol in hot weather.
However, she said the finding was unlikely to be down to people being made miserable by seeing others enjoying the good weather, as the effect was specific to unusually hot days, rather than summer days in general.
The researchers found that the suicide rate rose by 46.9% during the 1995 heat wave.
A similar run of hot weather in 2003 appeared to have little impact, possibly because high temperatures came in two distinct spells, giving people a chance to adapt.
During the 11-year period covered by the research, the average temperature in England topped 18C on 222 days.
There were 53,623 suicides – an average of 13.3 per day.
Three-quarters of all suicides were by men and this proportion remained constant over the study period.
The highest daily suicide count was recorded for 1 January.
The largest number of suicides took place on Mondays, with numbers declining as the week wore on.
Source: BBC News