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Environmental factors and risks of cognitive impairment and dementia: A systematic review and meta-analysis
Zhao YL, Qu Y, Ou YN, Zhang YR, Tan L, Yu JT.. Ageing research reviews, 2021-10-29
Topic: Risk, prevention and care in population studies
Plain-language summary
Background Dementia is a challenging neurodegenerative disease. This systematic review aimed to summarize natural, physical, and social environmental factors that are associated with age-related cognitive impairment and dementia. Methods We systematically searched PubMed, EMBASE, Web of Science, and PsychINFO till January 11, 2021 for observational studies. The hazard ratio (HR), relative risk (RR), and odds ratio (OR) with 95% confidence interval (CI) were aggregated using random-effects methods. The quality of evidence for each association was evaluated. Results Of the 48,399 publications identified, there were 185 suitable for review across 44 environmental factors. Meta-analyses were performed for 22 factors. With high-to-moderate quality of evidence, risks were suggested in exposure to PM 2.5 (HR=1.24, 95%CI: 1.17-1.31), NO 2 (HR=1.07, 95%CI: 1.02-1.12), aluminum (OR=1.35, 95%CI: 1.14-1.59), solvents (OR=1.14, 95%CI: 1.07-1.22), road proximity (OR=1.08, 95%CI: 1.04-1.12) and other air pollutions, yet more frequent social contact (HR=0.82, 95%CI: 0.76-0.90) and more greenness (OR=0.97, 95%CI: 0.95-0.995) were protective. With low-to-very low quality, electromagnetic fields, pesticides, SO 2 , neighborhood socioeconomic status, and rural living were suggested risks, but more community cultural engagement might be protective. No significant associations were observed in exposure to PM 10 , NO x , noise, silicon, community group, and temperature. For the remaining 22 factors, only a descriptive analysis was undertaken as too few studies or lack of information. Conclusions This review highlights that air pollutions, especially PM 2.5 and NO 2 play important role in the risk for age-related cognitive impairment and dementia.
Cite this study APA, Vancouver, BibTeX · download .bib or .ris
APA 7th
Zhao, Y. L., Qu, Y., Ou, Y. N., Zhang, Y. R., Tan, L., & Yu, J. T. (2021). Environmental factors and risks of cognitive impairment and dementia: A systematic review and meta-analysis. Ageing research reviews. https://doi.org/10.1016/j.arr.2021.101504
Vancouver
Zhao YL, Qu Y, Ou YN, Zhang YR, Tan L, Yu JT. Environmental factors and risks of cognitive impairment and dementia: A systematic review and meta-analysis. Ageing research reviews. 2021. doi:10.1016/j.arr.2021.101504. PMID: 34755643.
BibTeX
@article{zhao2021-34755643,
author = {Zhao, Y. L. and Qu, Y. and Ou, Y. N. and Zhang, Y. R. and Tan, L. and Yu, J. T.},
title = {{Environmental factors and risks of cognitive impairment and dementia: A systematic review and meta-analysis}},
journal = {Ageing research reviews},
year = {2021},
doi = {10.1016/j.arr.2021.101504},
pmid = {34755643},
url = {https://doi.org/10.1016/j.arr.2021.101504}
}
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Key findings
- This systematic review aimed to summarize natural, physical, and social environmental factors that are associated with age-related cognitive impairment and dementia.
- Results Of the 48,399 publications identified, there were 185 suitable for review across 44 environmental factors.
- No significant associations were observed in exposure to PM 10 , NO x , noise, silicon, community group, and temperature.
Why it matters
This systematic review and meta-analysis found that some environmental exposures such as air pollution were associated with higher dementia risk, while more social contact and greenness were protective. It identifies associations only and does not test any treatment, cure or prevention.
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Study details
- Study designsystematic review
- Effect sizeHR=1.24; HR=1.07; OR=1.35
- Evidence strengthHigh
How this study scored 66/100
Published in a peer-reviewed journal, and it is a systematic review of all the studies on the question. Scored zero for sample size and studied in people because the record does not state it.
| Component | Points | Why |
|---|---|---|
| Journal tier | 7 / 10 | Tier 3 — peer-reviewed journal (Ageing research reviews) |
| Journal's citation record | 2 / 4 | Ageing Research Reviews: journal h-index 225 (OpenAlex, 2026-10-29) |
| Study design | 12 / 12 | A systematic review of all the studies on the question |
| Strength of evidence | 5 / 5 | Rated “high” in our summary |
| Peer-review validation | 10 / 10 | Peer-reviewed. Published as an article in a named peer-reviewed journal. |
| How recent | 3 / 5 | 2021 — 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) |
| Randomized / blinded | 0 / 2 | A review of other studies — randomization is not credited here |
| Times cited | 5 / 7 | Cited 126 times (OpenAlex, 2026-10-10) |
| Citations per year | 3 / 5 | 18.0 citations a year over 7 year(s) since 2021 |
| Impact for its field and year | 3 / 6 | Cited 3.2× the average for papers of its field and year (OpenAlex FWCI) |
| Cited by studies here | 3 / 6 | Cited by 10 other studies in this library |
| Still being cited | 3 / 4 | Cited 99 times in 2024–2026 (2026 still in progress; OpenAlex) |
| Senior author's track record | 2 / 4 | Last-listed author Jin‐Tai Yu: h-index 39 (OpenAlex, whole career) |
| Institution's track record | 1 / 3 | Fudan University: institution h-index 954 (OpenAlex) |
| Multicenter collaboration | 2 / 3 | OpenAlex lists 7 institution(s) in 1 country |
| Indexed in PubMed | 2 / 2 | Indexed in PubMed (PMID 34755643) |
| Free to read | 0 / 2 | Behind a paywall — scores zero |
| Total | 66 / 100 | — |
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