Examining the effect of smoking on suicidal ideation and attempts: triangulation of epidemiological approaches

Abstract

BackgroundPrevious literature has demonstrated a strong association between cigarette smoking, suicidal ideation and suicide attempts. This association has not previously been examined in a causal inference framework and could have important implications for suicide prevention strategies. AimsWe aimed to examine the evidence for an association between smoking behaviours (initiation, smoking status, heaviness, lifetime smoking) and suicidal thoughts or attempts by triangulating across observational and Mendelian randomisation analyses. MethodFirst, in the UK Biobank, we calculated observed associations between smoking behaviours and suicidal thoughts or attempts. Second, we used Mendelian randomisation to explore the relationship between smoking and suicide attempts and ideation, using genetic variants as instruments to reduce bias from residual confounding and reverse causation. ResultsOur observational analysis showed a relationship between smoking behaviour, suicidal ideation and attempts, particularly between smoking initiation and suicide attempts (odds ratio, 2.07; 95% CI 1.91-2.26; P < 0.001). The Mendelian randomisation analysis and single-nucleotide polymorphism analysis, however, did not support this (odds ratio for lifetime smoking on suicidal ideation, 0.050; 95% CI −0.027 to 0.127; odds ratio on suicide attempts, 0.053; 95% CI, −0.003 to 0.110). Despite past literature showing a positive dose-response relationship, our results showed no clear evidence for a causal effect of smoking on suicidal ideation or attempts. ConclusionsThis was the first Mendelian randomisation study to explore the effect of smoking on suicidal ideation and attempts. Our results suggest that, despite observed associations, there is no clear evidence for a causal effect.

Associations of cigarette smoking with psychiatric disorders: evidence from a two-sample Mendelian randomization study

“…The associations of smoking with depression, schizophrenia 41 , suicide ideation 42 and bipolar disorder 36 have been revealed in previous MR studies. The present study was based on more recent GWASs and comprehensively investigated the causal associations between smoking initiation and psychiatric traits.…”

The co-occurrence of smoking and suicide

“…Hence, researchers have aimed to find causal risk factors, which could inspire improvements of suicide intervention strategies. In this issue of the British Journal of Psychiatry , Harrison et al 1 examined whether tobacco smoking is a causal risk factor for potentially fatal behaviours such as suicidal ideations or attempts. Their aim was to triangulate the available evidence by testing for observational associations and causality.…”

“…Harrison et al observed cross-sectional associations of all self-reported smoking behaviours with suicide attempts and ideation in 45 825–109 688 UK Biobank participants. 1 Analyses were adjusted for age, gender and socioeconomic status. The strongest association was observed between smoking initiation and suicide attempt (odds ratio, 2.07; 95% CI 1.91–2.26; P < 0.001).…”

“…Furthermore, >50% of the SNPs in the genetic instrument explained more variance in the outcome (i.e. suicide attempts) than in smoking initiation (see Supplementary Table 3 in Harrison et al 1 ), which increases the likelihood of reverse causation. Follow-up analyses suggested that risk-taking behaviour, which is well known to affect both substance use and (auto-)aggressive behaviours, 2 might underlie the association between smoking and suicidality.…”

“…2 The present study by Harrison et al is no exception: tobacco smoking had no causal effect on suicidal ideation and self-harm. 1 Instead of focussing on modifiable risk factors, perhaps suicide prevention research should shift from causal frameworks to prediction. Unfortunately, although suicide prediction models have overall very good accuracy, their predictive validity of correctly classifying a suicide death is near zero, i.e.…”