Prevalence of tobacco smoking in people at clinical high-risk for psychosis: Systematic review and meta-analysis

: Several hypotheses have been proposed to explain why individuals with psychosis consume more tobacco compared with the general population, but the reasons remain unclear. The phases predating the onset of psychosis could provide an interesting framework to clarify this association. The aim of this systematic review and meta-analysis is to provide an updated and comprehensive synthesis of the association between tobacco smoking and Clinical High Risk for Psychosis (CHRP) status. We performed a multistep systematic PRISMA/MOOSE-compliant electronic search for articles published from inception until October 1st, 2021. Web of Science was searched, complemented by a manual search of original articles reporting the outcome of tobacco consumption (defined as the number of individuals which were smoking tobacco at baseline) in a group of CHR-P patients versus healthy controls (HC). We employed quality assessment of the included studies with Newcastle Ottawa Scale (NOS). The effect size for the primary outcome was the odds ratio (OR) of smoking tobacco in CHR-P samples vs HC. We performed a random-effects model meta-analysis, assessment of heterogeneity with I2 index, sensitivity analyses excluding one study at a time for primary outcome, meta-regressions with four independent moderators (mean age, female ratio, sample size, NOS) and assessment of publication bias with funnel plot and Egger's test. We included 21 independent articles, totalling 2018 CHR-P individuals (mean age of 21.35 ± 2.91 years and average female ratio of 41 ± 7 %) and 1160 HC (mean age of 22.42 ± 3.70 years and average female ratio of 45 ± 11 %). The NOS score was 6.52 ± 1.25 (range from 0 to 9). The OR of smoking status was 2.22 (95%CI 1.74-2.84, p < 0.01). Heterogeneity (I2) was 24.09 (p = 0.16). Sensitivity analyses, removing one study at a time, revealed the robustness of our main finding. Meta-regressions did not reveal any significant association between the moderators and the main outcome. Visual inspection of the funnel plot and Egger's test did not reveal evident publication bias. Our main finding of an increased OR of smokers in the CHR-P individuals compared to healthy controls corroborates the accumulation of unhealthy lifestyles in this vulnerable group. This does not demonstrate any causal association between tobacco smoking and incidence of psychosis, which should be investigated in future prospective cohorts. In conclusion, the window of opportunity represented by CHR-P status should involve more efficient physical health screening and better investigating the aetiological impact of smoking in the development of psychosis.