Air Pollution and Incidence of Dementia: A Systematic Review and Meta-analysis.
Level 3 - non-randomized controlled study
Systematic review and meta-analysis of observational cohort studies
PubMed 36288998 · doi:10.1212/WNL.0000000000201419
What was done
Researchers systematically searched six databases (PubMed, MEDLINE, EMBASE, PsycINFO, Scopus, Web of Science) through August 2021 for population-based cohort studies evaluating the association between air pollution exposure (PM2.5, NOx, NO2, O3) and incident dementia in individuals aged >40 years. Data were extracted by two independent investigators, and pooled hazard ratios (HRs) per pollutant increment were calculated using random-effects models following PRISMA guidelines.
What was found
The review included 20 cohort studies (17 meta-analyzed), comprising 91,391,296 participants and 5,521,111 (6%) incident dementia diagnoses. - PM2.5 (12 studies): Dementia risk increased by 3% per 1 μg/m³ increment (HR 1.03, 95% CI [1.02, 1.05]; I² = 100%). - NOx (5 studies): HR 1.05 per 10 μg/m³ increment (95% CI [0.99, 1.13]; I² = 61%). - NO2 (6 studies): HR 1.03 per 10 μg/m³ increment (95% CI [1.00, 1.07]; I² = 94%). - O3 (4 studies): HR 1.01 per 10 μg/m³ increment (95% CI [0.91, 1.11]; I² = 82%).
Why it matters
This meta-analysis quantitatively links fine particulate air pollution (PM2.5) to an increased risk of incident dementia across a very large pooled population, identifying an environmental target for dementia prevention strategies.
Limits
All included studies were observational cohorts, precluding causal inference. There was extreme statistical heterogeneity across studies (I² up to 100% for PM2.5). Meta-analyses for gaseous pollutants (NOx, NO2, O3) were based on very few studies (4 to 6), limiting statistical power.
Cited by
- partial Particulate matter air pollution is a primary contributing factor to the development of dementia.