All-cause mortality increases during periods of high ambient temperature, but the short-term effect of temperature on suicide and homicide is not known. Seasonal fluctuations in suicide and homicide have been observed in different populations and temperature is one suggested reason for this observation. Our aim was firstly to assess the relationship between daily temperature and daily suicide and homicide counts and secondly to establish whether heat waves are associated with increased suicides.
Material and Methods:
Daily death counts from suicide and homicide between January 1, 1993, and December 31, 2003, in England and Wales were the outcome of interest. Time-series regression analysis was used to explore and quantify the relationship between daily counts and daily temperature after controlling for time-varying confounders. Natural cubic splines were used to model the effect of temperature on death counts across the temperature range. The impact of 2 heat waves on suicide was estimated by episode analysis.
No spring or summer peak in suicides or homicides were found. However, regression analyses demonstrated a nonlinear relationship between suicide, homicide, and temperature. There was evidence of a high-temperature threshold effect, with each 1°C increase above 18°C being associated with a 4% and 9% rise in suicide and homicide, respectively. For suicide, the high-temperature effect was strongest for violent suicide. Suicide increased during the 1995 heat wave compared with adjacent years, whereas no effect was seen during the 2003 heat wave.
There is increased risk of suicide and homicide at high temperatures in England and Wales, with some evidence that heat waves resulted in increased mortality from suicide. Although these findings require replication in other populations and geographic areas, they are of particular interest given that global temperatures are expected to rise.