Meta-analysis of 61 cohort studies: current smoking linked to 31% higher dementia risk

A systematic review and meta-analysis in EClinicalMedicine pooled 61 cohort studies with approximately 2.8 million participants to estimate how smoking relates to dementia risk sciencedirect.comEClinicalMedicinesciencedirect.comOpen source ↗. It updates a 2015 review that contributed 34 studies. The authors searched PubMed, Embase, CENTRAL and PsycINFO from January 2013 to 31 August 2026.

Risk by dementia type and smoking status

Current smoking was associated with higher risk of all-cause dementia (RR 1.31, 95% CI 1.23–1.39; 39 studies), Alzheimer's disease (RR 1.40, 1.08–1.80; 15 studies) and vascular dementia (RR 1.52, 1.20–1.93; 9 studies). Former smoking was not associated with any outcome. Former smokers had a lower risk of all-cause dementia than current smokers (RR 0.81, 0.75–0.88).

Pooled estimates came from random-effects models. Heterogeneity (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 authors also ran subgroup analyses and meta-regression by baseline age, ethnicity, follow-up duration and adjustment for sex, education and APOE ε4 genotype, and assessed risk of bias with the ROBINS-E tool.

Dose–response and attributable fraction

Risk increased with smoking intensity: the pooled RR was 1.16 (95% CI 1.09–1.23) at 10 cigarettes per day and 1.34 (1.18–1.51) at 20 cigarettes per day sciencedirect.comEClinicalMedicinesciencedirect.comOpen source ↗. The communality-weighted population attributable fraction of smoking for dementia was 2.2% (95% CI 1.7–2.8).

The authors note that the data are observational, so causality cannot be established. The estimates refer to clinically diagnosed dementia syndromes (DSM/ICD), not to biologically defined disease. They say the findings support considering dementia and brain health outcomes in national tobacco control strategies and campaigns. Studies with objectively verified smoking histories are needed to clarify how age at cessation and time since quitting affect dementia risk, and whether these effects interact with total years of active smoking. The study reports no funding.