The association between tobacco smoking and depression and anxiety in people with multiple sclerosis: A systematic review.

BACKGROUND:The link between tobacco smoking and Multiple Sclerosis (MS) onset and progression is well-established. While clinical levels of depression and anxiety are highly prevalent in people living with MS (plwMS), and both are recognized as common MS-related symptoms, the relationships between smoking behavior and depression and anxiety are unclear. This systematic review aimed to synthesize evidence on the relationships between current-smoking and former-smoking and depression and anxiety in plwMS. METHODS:Systematic review of all studies investigating associations between tobacco smoking and depression and anxiety in plwMS was conducted. Relevant studies published before 26 April 2022 were identified by searching seven databases; MEDLINE® (Ovid and PubMed), Embase, CINAHL®, Cochrane Library and PsycInfo), and citation and reference list checking. Joanna Briggs Institute Critical Appraisal Checklists for respective study designs assessed the risk of bias. RESULTS:Thirteen publications reporting on 12 studies met study inclusion criteria. Nine of 12 studies examining current-smoking and depression in plwMS identified a positive association. Four prospective studies provided evidence supporting a causal smoking-depression relationship, with 1.3-2.3-fold higher depression prevalence found in current-smokers than non-smokers. Three cross-sectional studies found no smoking-depression association. Four of five included studies found current-smoking was associated with anxiety, with three prospective studies indicating anxiety prevalence was around 20% higher in current-smokers. Former-smoking was associated with increased prevalence of depression, but not anxiety. CONCLUSION:We provide strong evidence for increased depression prevalence in plwMS who are either current-smokers or former-smokers. However, only current-smoking was associated with increased prevalence of anxiety.