Geospatial analyses of suicide mortality distribution

The distribution of suicide mortality in Austria follows a time-stable and specific pattern. Styria, parts of Carinthia and Salzburg traditionally show the highest suicide mortality in our country (Figure 1, SMRs). However, there is little geospatial research to understand how this characteristic pattern of mortality can be explained.

Figure 1.
Fig 1

Availability of mental health service providers and suicide rates in Austria: a nationwide study.

There is increasing evidence that the access to mental healthcare services may have impact on mental health outcomes as suicide rates. The first aim was to examine in a small-area analysis, whether the availability of professionals providing mental health treatment in Austria may have an effect on regional suicide rates. A hierarchical Bayesian model accounting for spatially correlated random effects using an intrinsic conditional autoregressive prior that incorporates the neighborhood structure of districts and assuming a Poisson distribution for the observed number of suicides was used to estimate effects of mental healthcare access (density of general practitioners, psychiatrists and psychotherapists) in Austria. The results showed that regional socio-economic factors were correlated with the density of psychiatrists and psychotherapists. Only the density of psychotherapists showed a significant effect on suicide rates, after adjustment for socio-economic factors the observed effects were lost. In the final model only the socio-economic component remained significant. We conclude that the availability of specialized mental health service providers is associated with regional socio-economic factors, and these seem to be a stronger predictor of suicide rates rather than the availability service providers itself. This suggests that the acces to healthcare (or barriers to access) might be a crucial aspect of suicide prevention. (Psychiatric Services. 2010;61:1198-203.)

Geospatial Examination of Lithium in Drinking Water and Suicide Mortality

There is some evidence that natural levels of lithium in drinking water may have a protective effect on suicide mortality. To evaluate this possible association, we examined data of local lithium levels in drinking water and suicide mortality at district level in Austria. Multivariate regression models were adjusted for well-known socioeconomic factors known to influence suicide mortality in Austria. Sensitivity analyses and weighted least squares regression were used to challenge the robustness of the results. The overall suicide rate were inversely associated with lithium levels in drinking water and remained significant after sensitivity analyses and adjustment for socioeconomic factors. In replicating and extending previous results from Japan and Texas, this study provided evidence that geographic regions with higher natural lithium concentrations in drinking water are associated with lower suicide mortality rates (The British Journal of Psychiatry 2011; 198: 346-350).

Further statistical analyses by global and local spatial regression models took non-stationarity into account. A Geographically Weighted Regression (GWR) model was applied that used an adaptive, bisquare kernel function and the significant independent variables indicated by spatial autoregressive (SAR) models. The association between lithium levels in drinking water and suicide mortality could be confirmed by a global spatial regression model. In addition, a local spatial regression model showed that the association was mainly driven by the eastern parts of Austria. The application of the GWR approach also opens new avenues in the collaboration between Geographic Information Science (GISc), medicine, and even criminology, such as exploring the spatial association between violent or impulsive crime and lithium content in drinking water (International Journal of Health Geographics. 2012;11:19).

Up to now, it has been assumed that lithium in drinking water originated from natural sources (natural-lithium-hypothesis) such as lithium containing rock and soil. It has not been considered that lithium prescribed to patients may accumulate via waste water in ground water aquifers after urinary excretion. There are numerous reports pointing to the problem of pharmaceuticals in waste water. There is evidence that the groundwater in regions with high prescription and over-the counter rates of pharmaceuticals, has higher levels of pharmaceuticals than other regions. It can be assumed that lithium, which has been used in psychiatry for more than 60 years, has accumulated in drinking water reservoirs and is therefore responsible for the non-random distribution of lithium in drinking water across Austrian districts.

Lithium in drinking water and prescriptions effects on suicide mortality
With this in mind, a further project funded by FWF 2013-2015 evaluated the hypothesis that the previously found association of lithium in drinking water and suicide rates may be a function of regional lithium prescription rates rather than an effect of natural lithium occurrence.

Figure 2.

The results of the project, however, do not suggest that lithium in drinking water is substantialy affected by prescriptions of lithium. On the other hand, prescriptions show no correlation with suicide rates, so that the otherwise known suicide preventive effect of lithium treatment can not be displayed on an ecological level. It may therefore still be hypothesized that lithium deposits in drinking water originate from natural sources and are associated in an still not understood way (because of their low doses) with lower suicide mortality (British Journal of Psychiatry. 2015;207:64–71).

© Suicide Research Group at the Medical University of Vienna