Lithium levels in drinking water predicted the ratio of attempted to completed suicides in regions with high incidence of affective disorders: Insights from ecological study

Introduction: Lithium has demonstrated significant antisuicidal effects: it significantly reduces the high excess overall mortality of patients with affective disorders. Methods: Public drinking water samples were collected in 53 Lithuanian municipalities during a two-month period. Linear models used lithium level in public drinking water as predictor and ratio of suicide attempts to suicide mortality as outcomes across the municipalities. Results: Lithium in drinking water predicted the ratio of attempted to completed suicides (A/S) nonlinearly, described by a U-shaped curve. The curves for visualization of the association of incidence of affective disorders and suicide standard mortality rate with lithium level displayed significant suicide curve decrements and invers direction in affective disorders curve. Multivariate regression model for ratio A/S in high lithium exposure group (> 7 µg/L, N = 26) suggests that the lithium level can explain 54.3 % of variance of ratio A/S in municipalities with exposure of lithium above median and with high incidence of affective disorders. Conclusions: The findings provide confirmatory evidence that in municipalities with high incidence of affective disorders higher lithium levels in the public drinking water are associated with higher ratio A/S due to an unchanging number of suicide attempts and due to decreasing suicide lethal outcomes. Limitations: Nevertheless, the methods employed detected several factors with well-established associations with suicide. Finally, cohort, prospective or intervention studies are needed to verify the causal inverse relationship of these variables and to speculate the mechanism for this relationship.