Systematic review and meta-analysis

Does tobacco use cause psychosis?

Summary of a review study by Pedro Gurillo, Sameer Jauhar, Robin M. Murray and James H. MacCabe (NIHR Maudsley Biomedical Research Centre), published in The Lancet (August 2015).

Background
Although the association between psychotic illness and cigarette smoking is well known, the reasons are unclear why people with psychosis are more likely to smoke than are the general population. We aimed to test several hypotheses. First, that daily tobacco use is associated with an increased risk of psychotic illness in both case-control and prospective studies. Second, that smoking is associated with an earlier age at onset of psychotic illness. Finally, that an earlier age at initiation of smoking is associated with an increased risk of psychosis. We also aimed to derive an estimate of the prevalence of smoking in patients presenting with their first episode of psychosis.

Methods
We searched Embase, Medline, and PsycINFO and selected observational studies in which rates of smoking were reported in people with psychotic disorders, compared with controls. We calculated the weighted mean difference for age at onset of psychosis and age at initiation of smoking. For categorical outcomes, we calculated odds ratios from cross-sectional studies and risk ratios from prospective studies.

Findings
Of 3717 citations retrieved, 61 studies comprising 72 samples met inclusion criteria. The overall sample included 14?555 tobacco users and 273?162 non-users. The prevalence of smoking in patients presenting with their first episode of psychosis was 0·57 (95% CI 0·52–0·62; p<0·0001). In case-control studies, the overall odds ratio for the first episode of psychosis in smokers versus non-smokers was 3·22 (95% CI 1·63–6·33), with some evidence of publication bias (Egger's test p=0·018, Begg's test p=0·007). For prospective studies, we calculated an overall relative risk of new psychotic disorders in daily smokers versus non-smokers of 2·18 (95% CI 1·23–3·85). Daily smokers developed psychotic illness at an earlier age than did non-smokers (weighted mean difference ?1·04 years, 95% CI ?1·82 to ?0·26). Those with psychosis started smoking at a non-significantly earlier age than did healthy controls (?0·44 years, 95% CI ?1·21 to 0·34).

Interpretation
Daily tobacco use is associated with increased risk of psychosis and an earlier age at onset of psychotic illness. The possibility of a causal link between tobacco use and psychosis merits further examination.

Funding
NIHR Maudsley Biomedical Research Centre.

Read the full article (The Lancet, August 2015, open access).
Listen to the Lancet podcast interview with Sameer Jauhar and James MacCabe (MP3 audio).

  • EGYPTIAN STUDY

    Second hand smoking and children’s mental health

    Abstract
    Background: Second hand smoke (SHS) might affect mental health of children as many mental disorders have an onset in youth, a time when SHS exposure is high. Objectives: Investigation of the potential association of SHS exposure with children’s mental health disorders.
    Methodology: Forty five SHS exposed Egyptian children were enrolled as group I; all of them had at least one smoking parent and or were exposed to environmental tobacco smoke while group II included thirty age and sex well matched controls, with neither history of parental smoking nor exposures to environmental tobacco smoke. For all studied children, complete history taking, thorough clinical examination, psychometric assessment using Pediatric Symptom Checklist (PSC), Strengths and Difficulties Questionnaire (SDQ) and IQ measurement were done. DSM IV TR criteria were used to confirm any suspected behavioral and or psychiatric disorder. Laboratory assessment of second hand smoke was carried out measuring urinary cotinine levels.
    Results: SHS exposed children had significantly higher mean value of urinary cotinine level, total PSC, and SDQ scores compared to controls p<001, p<0.001, p<0.05 respectively). Mean values of Attention Deficit Hyperactivity Disorder (ADHD), internalization and externalization behaviors’ sub scores of PSC were significantly higher in SHS children compared to controls. Meanwhile, mean values of emotion, conduct, ADHD, and peer problem SDQ sub-scores were higher in SHS children compared to controls but the comparison was only statistically significant for ADHD sub-score while prosocial problem sub-score was significantly lower in SHS children compared to controls. In studied SHS children, degree of smoking significantly positively correlated with PSC internalization behavior sub-score and emotion sub-score of SDQ while smoking index significantly positively correlated with ADHD sub-score of SDQ. Meanwhile, prosocial sub-score of SDQ and urinary cotinine level were significantly negatively correlated. In conclusion, SHS exposure significantly compromised mental health of the studied sample of Egyptian SHS exposed children.
    Read the full article.