EClinicalMedicine · Nov 2026
Smoking and dementia risk: an updated systematic review and meta-analysis of 61 prospective cohort studies and implications for tobacco control
By Siervo M, Brain J, Beasley S et al.
Background Smoking has been identified as a modifiable dementia risk factor by three Lancet Commissions, yet dementia remains absent from most tobacco control strategies. The magnitude of the association across dementia subtypes, smoking categories, and population characteristics has not been comprehensively synthesised since 2015. Methods PubMed, Embase, CENTRAL, and PsycINFO were searched from January 2013 to 31 August 2026, updating the 2015 review, which contributed 34 studies. Random-effects meta-analyses (Restricted Maximum Likelihood (REML) with Hartung–Knapp–Sidik–Jonkman adjustment) estimated pooled relative risks (RRs) with 95% confidence intervals (CIs). Subgroup analyses with tests for interaction and meta-regression examined effect modification by baseline age, ethnicity, follow-up duration, and adjustment for sex, education and Apolipoprotein E ε4 (APOE ε4) genotype. Risk of bias was assessed using Risk Of Bias In Non-randomized Studies of Exposures (ROBINS-E). Heterogeneity was assessed using Cochran’s Q, I² and τ² and publication bias using funnel plots and Egger’s test. Dose–response analysis of smoking and dementia risk was performed. Smoking population attributable fractions (PAF, unweighted and communality-weighted) for the risk of dementia were calculated. This study is registered with PROSPERO, CRD42025644539. Findings Sixty-one cohort studies (approximately 2.8 million participants) were included. Current smoking was associated with increased risk of all-cause dementia (RR 1.31 [95% CI 1.23–1.39]; number of studies (k) = 39), Alzheimer’s disease (1.40 [1.08–1.80]; k = 15), and vascular dementia (1.52 [1.20–1.93]; k = 9). Former smoking was not associated with any outcome, and former smokers had a lower risk of all-cause dementia than current smokers (RR 0.81 [0.75–0.88]). I² ranged from 0% to 80%. Egger’s test suggested small-study effects only for current smoking and all-cause dementia (P = 0.09). The communality-weighted PAF for smoking and dementia was 2.2% (95% CI 1.7–2.8). Dementia risk increased with smoking intensity as the pooled RR was 1.16 (95% CI 1.09–1.23) at 10 cigarettes per day and rose to 1.34 (95% CI 1.18–1.51) at 20 cigarettes per day. Interpretation Current smoking is consistently associated with higher risk of all dementia outcomes and increases with smoking intensity. Estimates refer to clinically diagnosed dementia syndromes [Diagnostic and Statistical Manual of Mental Disorders/International Classification of Diseases (DSM/ICD)] and not to biologically defined disease. Although causality cannot be established from observational data, these findings support considering dementia and brain health outcomes in national tobacco control strategies and associated campaigns. Future work using objectively verified smoking histories is needed to clarify how age at cessation and time since quitting influence dementia risk and whether these effects interact with total years of active smoking. Funding None.