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Ambient air pollution and clinical dementia: systematic review and meta-analysis
Wilker EH, Osman M, Weisskopf MG. BMJ, 2023-04-05
Topic: Risk, prevention and care in population studies
Objective To investigate the role of air pollutants in risk of dementia, considering differences by study factors that could influence findings. Design Systematic review and meta-analysis. Data sources EMBASE, PubMed, Web of Science, Psycinfo, and OVID Medline from database inception through July 2022. Eligibility criteria for selecting studies Studies that included adults (≥18 years), a longitudinal follow-up, considered US Environmental Protection Agency criteria air pollutants and proxies of traffic pollution, averaged exposure over a year or more, and reported associations between ambient pollutants and clinical dementia. Two authors independently extracted data using a predefined data extraction form and assessed risk of bias using the Risk of Bias In Non-randomised Studies of Exposures (ROBINS-E) tool. A meta-analysis with Knapp-Hartung standard errors was done when at least three studies for a given pollutant used comparable approaches. Results 2080 records identified 51 studies for inclusion. Most studies were at high risk of bias, although in many cases bias was towards the null. 14 studies could be meta-analysed for particulate matter 2.5 ). The overall hazard ratio per 2 μg/m 3 PM 2.5 was 1.04 (95% confidence interval 0.99 to 1.09). The hazard ratio among seven studies that used active case ascertainment was 1.42 (1.00 to 2.02) and among seven studies that used passive case ascertainment was 1.03 (0.98 to 1.07). The overall hazard ratio per 10 μg/m 3 nitrogen dioxide was 1.02 ((0.98 to 1.06); nine studies) and per 10 μg/m 3 nitrogen oxide was 1.05 ((0.98 to 1.13); five studies). Ozone had no clear association with dementia (hazard ratio per 5 μg/m 3 was 1.00 (0.98 to 1.05); four studies). Conclusion PM 2.5 might be a risk factor for dementia, as well as nitrogen dioxide and nitrogen oxide, although with more limited data. The meta-analysed hazard ratios are subject to limitations that require interpretation with caution. Outcome ascertainment approaches differ across studies and each exposure assessment approach likely is only a proxy for causally relevant exposure in relation to clinical dementia outcomes. Studies that evaluate critical periods of exposure and pollutants other than PM 2.5 , and studies that actively assess all participants for outcomes are needed. Nonetheless, our results can provide current best estimates for use in burden of disease and regulatory setting efforts. Systematic review registration PROSPERO CRD42021277083.
Cite this study APA, Vancouver, BibTeX · download .bib or .ris
APA 7th
Wilker, E. H., Osman, M., & Weisskopf, M. G. (2023). Ambient air pollution and clinical dementia: systematic review and meta-analysis. BMJ. https://doi.org/10.1136/bmj-2022-071620
Vancouver
Wilker EH, Osman M, Weisskopf MG. Ambient air pollution and clinical dementia: systematic review and meta-analysis. BMJ. 2023. doi:10.1136/bmj-2022-071620. PMID: 37019461.
BibTeX
@article{wilker2023-37019461,
author = {Wilker, E. H. and Osman, M. and Weisskopf, M. G.},
title = {{Ambient air pollution and clinical dementia: systematic review and meta-analysis}},
journal = {BMJ},
year = {2023},
doi = {10.1136/bmj-2022-071620},
pmid = {37019461},
url = {https://doi.org/10.1136/bmj-2022-071620}
}
Built from the record alzhub holds for this paper, not looked up. Volume, issue and page numbers are not held in the record. Check the citation against the original before you use it.
Key findings
- Results 2080 records identified 51 studies for inclusion.
- The overall hazard ratio per 2 μg/m 3 PM 2.5 was 1.04 (95% confidence interval 0.99 to 1.09).
- The overall hazard ratio per 10 μg/m 3 nitrogen dioxide was 1.02 ((0.98 to 1.06); nine studies) and per 10 μg/m 3 nitrogen oxide was 1.05 ((0.98 to 1.13); five studies).
- Nonetheless, our results can provide current best estimates for use in burden of disease and regulatory setting efforts.
Why it matters
Across 51 studies, the overall link between fine particulate air pollution and dementia was not statistically significant, and most studies had a high risk of bias. The authors note their results can still provide current best estimates for burden of disease and regulatory purposes.
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Study details
- Study designmeta-analysis
- Effect sizePM2.5 HR 1.04 per 2 ug/m3 (95% CI 0.99-1.09) overall; 1.42 (1.00-2.02) with active case ascertainment
- Evidence strengthModerate
Limitations
Heterogeneous exposure assessment and outcome ascertainment; most studies high risk of bias; limited data on pollutants other than PM2.5.
How this study scored 69/100
Published in a leading specialty journal, and it is a meta-analysis pooling many studies. Scored zero for sample size and studied in people because the record does not state it. We have no data on free to read, so that was left out: it earned 68 of the 98 points we could judge it on, which is 69 out of 100.
| Component | Points | Why |
|---|---|---|
| Journal tier | 9 / 10 | Tier 2 — leading specialty journal (BMJ) |
| Journal's citation record | 3 / 4 | BMJ: journal h-index 413 (OpenAlex, 2026-10-29) |
| Study design | 12 / 12 | A meta-analysis pooling many studies |
| Strength of evidence | 3 / 5 | Rated “moderate” in our summary |
| Peer-review validation | 10 / 10 | Peer-reviewed. Published as an article in a named peer-reviewed journal. |
| How recent | 3 / 5 | 2023 — within 6 year(s) of the newest study here |
| Sample size | 0 / 4 | Participant count not stated — scores zero (not stated in the record — scored 0) |
| Effect reported | 3 / 3 | Effect reported with a statistic (interval, p-value, ratio or similar) |
| Studied in people | 0 / 3 | Not stated whether this was studied in people — scores zero (not stated in the record — scored 0) |
| Randomised / blinded | 0 / 2 | A review of other studies — randomisation is not credited here |
| Times cited | 5 / 7 | Cited 185 times (OpenAlex, 2026-10-10) |
| Citations per year | 4 / 5 | 37.0 citations a year over 5 year(s) since 2023 |
| Impact for its field and year | 3 / 6 | Cited 7.2× the average for papers of its field and year (OpenAlex FWCI) |
| Cited by studies here | 2 / 6 | Cited by 8 other studies in this library |
| Still being cited | 3 / 4 | Cited 168 times in 2024–2026 (2026 still in progress; OpenAlex) |
| Senior author's track record | 3 / 4 | Last-listed author Marc G. Weisskopf: h-index 75 (OpenAlex, whole career) |
| Institution's track record | 3 / 3 | Harvard University: institution h-index 3,235 (OpenAlex) |
| Multi-centre collaboration | 0 / 3 | OpenAlex lists 1 institution(s) in 1 country — scores zero (affiliation lists can be incomplete) |
| Indexed in PubMed | 2 / 2 | Indexed in PubMed (PMID 37019461) |
| Free to read | — / 2 | Access not recorded — left out of this score |
| Points | 68 / 98 | Scored on 19 of 20 parts. We have no data for the rest, so they are left out: 68 of the 98 points we could judge it on is 69 out of 100. |
| Total | 69 / 100 | — |
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