The hypothesis of an impact of ozone on the occurrence of completed and attempted suicides.

Air pollution and its impact on human health are of growing concern throughout the world. Recent studies have mainly focussed on respiratory and vascular mortality. The existence of seasonality of ozone distribution and also of the occurrence of suicides as well as suicide attempts is generally accepted, though an interconnection of both phenomena has not yet been established. This hypothesis of an influence of ozone on the occurrence of suicidality was tested on preliminary data (1008 suicides and 917 suicide attempts from a larger epidemiological sample in Middle-Franconia from 2004 to 2007). A higher suicide rate than expected could be observed from July to September, whereas the rates of the suicide attempts did not show a seasonality in relation to ozone levels. To further strengthen the hypothesis, ozone levels differed significantly (T = -2.5; p = 0.014) between days where one or no suicide were observed (mean ozone: 79.8 microg/m(3); SD: 36.3) and days with two or more suicides (mean ozone: 86.4 microg/m(3); SD: 39.4). This phenomenon might be explained including sociological, biological as well as psychological effects. Sociologically, behaviour precipitating suicide might be influenced by climatic variables such as the weather or air pollution causing fatigue or cardio-respiratory symptoms influencing individual well-being in general thereby possibly leading to the decision to end one's life. Biologically, ozone is able to influence the immune system, is a strong trigeminal irritant and might influence neurotransmitter systems such as serotonin, which are known to vary with season and play a major role in impulsivity, aggression, depression and thereby suicidality. Putative psychological explanations for the suicide peak in summer include the influence of a higher ambient temperature leading individuals to a more disinhibited, aggressive and violent behaviour possibly resulting in an increased proneness for suicidal acts that is influenced by ozone. This might lead one to speculate whether ozone is able to account - at least amongst others - for the seasonal distribution of suicides or might even be a causative agent in the multifactorial genesis of a suicide. If this hypothesis is found to be true, further research should focus on the underlying mechanisms. Furthermore, this might be a strong argument to further encourage environment protection.