Objective: Investigating diurnal variation in the timing of suicidal behaviours offers opportunity to better understand its various proximal risk factors. Acute use of alcohol is a potent proximal risk factor for suicidal behaviour, though the nature of this risk is poorly understood. The aim of this study was to compare the diurnal variation in time of poison ingestion between deliberate self-poisonings that involve alcohol versus those that do not.
Methods: A retrospective analysis of consecutive presentations to a toxicology service following deliberate self-poisoning, 1996-2016. An independent samples Kolmogorov-Smirnov test was performed to test the null hypothesis that the diurnal distribution of poison ingestion time was equal across self-poisonings that did and did not involve alcohol co-ingestion. Presence of circadian rhythmicity was established using cosinor analysis.
Results: A total of 11,088 deliberate self-poisoning records, for 7467 patients (60.8% females), were included in the analysis. In all, 31.3% of the total records involved alcohol co-ingestion. Distribution of exposure time was significantly different between deliberate self-poisonings that did and did not involve alcohol ( p < 0.001). The alcohol co-ingestion group showed a significantly greater prominent peak with poisoning occurring later in the evening (~20:00 hours) compared to poisonings that did not involve alcohol (~18:00 hours).
Conclusion: This study exposed the differential diurnal patterns in deliberate self-poisoning according to the presence of alcohol co-ingestion. This analysis adds to the accumulating evidence that suicidal behaviour that involves alcohol co-ingestion represents a distinct subtype, which may be driven by alcohol consumption patterns in society. This also means that this large proportion of deliberate self-poisonings may not otherwise have occurred if it were not for alcohol consumption, underscoring the importance of drug and alcohol services for alcohol-related self-harm.
Keywords: Alcohol; circadian; deliberate self-poisoning; diurnal; rhythmicity.