Home › Research › Risk factors
Carbonaceous Components Underlying Wildfire Smoke PM 2.5 -Associated Alzheimer’s Disease and Related Dementias in Older US Adults
Jin Z, Xu K, Qi M, Zhu Q, Yang B, Ferrada GA, Fu JS, Scovronick N et al.. medRxiv, 2026-10-11
Topic: Air pollution and environmental exposures
Wildfire smoke exposure is increasing across the U.S., but the long-term neurological effects of smoke-specific fine particulate matter (PM 2.5 ) and its carbonaceous components remain uncertain. Using Medicare data from 2002 through 2019, we examined incident Alzheimer’s disease (AD) and Alzheimer’s disease and related dementias (ADRD) among 39,678,630 fee-for-service Medicare beneficiaries followed from 2005 through 2019. We identified 3,501,414 incident AD cases over 258.5 million person-years and 8,377,416 incident ADRD cases over 248.6 million person-years. We linked the cohort with annual, high-resolution estimates of smoke and non-smoke PM 2.5 mass and carbonaceous components (elemental and organic carbon) and fitted stratified Cox proportional hazards models. Per 1 µg/m 3 increase, smoke PM 2.5 was associated with incident AD (hazard ratio [HR], 1.015, 95% confidence interval [CI], 1.005-1.026) and ADRD (1.029 [1.024-1.035]). Smoke carbonaceous fraction was also associated with AD (1.063 [1.042-1.085]) and ADRD (1.090 [1.077-1.103]). Within the ADRD endpoint, smoke-related associations exceeded their corresponding non-smoke associations on a per-unit-mass basis. Per interquartile range, associations were smaller for smoke PM 2.5 (AD, 1.005 [1.002-1.008]; ADRD, 1.009 [1.008-1.011]) than for non-smoke PM 2.5 (AD, 1.086 [1.079-1.094]; ADRD, 1.048 [1.043-1.053]). Associations varied across geographic, racial, socioeconomic, and clinical subgroups. Long-term wildfire smoke exposure, particularly its carbonaceous fraction, was associated with higher incidence of AD and ADRD among older U.S. adults. The associations correspond to 2,284 and 11,142 incident cases per year of AD and ADRD attributable to smoke PM 2.5 among older Medicare beneficiaries, with the carbonaceous fraction accounting for most of this burden. These findings support the use of source-resolved and composition-specific smoke metrics in dementia research and wildfire-smoke health-impact assessments.
Key findings
- Per 1 µg/m 3 increase, smoke PM 2.5 was associated with incident AD (hazard ratio [HR], 1.015, 95% confidence interval [CI], 1.005-1.026) and ADRD (1.029 [1.024-1.035]).
- Smoke carbonaceous fraction was also associated with AD (1.063 [1.042-1.085]) and ADRD (1.090 [1.077-1.103]).
- Long-term wildfire smoke exposure, particularly its carbonaceous fraction, was associated with higher incidence of AD and ADRD among older U.S. adults.
- These findings support the use of source-resolved and composition-specific smoke metrics in dementia research and wildfire-smoke health-impact assessments.
New to this subject? Start with our plain-English guide: Risk factors, ranked →
Study details
- Evidence strengthModerate
How this study scored 16/100
Preprint — not yet peer-reviewed. It scored 24 on the same rubric, but non-peer-reviewed sources are capped at 16, so it shows as 16. Scored zero for study design, sample size, effect reported, studied in people and randomised / blinded because the record does not state it. We have no data on times cited, citations per year, impact for its field and year, cited by studies here, still being cited, senior author's track record, institution's track record and multi-centre collaboration, so those were left out: it earned 15 of the 62 points we could judge it on, which is 24 out of 100.
| Component | Points | Why |
|---|---|---|
| Journal tier | 2 / 10 | Tier 4 — not a peer-reviewed journal (medRxiv) |
| Journal's citation record | 0 / 4 | Not a journal article, so the journal's record does not count |
| Study design | 0 / 12 | No study design recorded — scores zero, not guessed (not stated in the record — scored 0) |
| Strength of evidence | 3 / 5 | Rated “moderate” in our summary |
| Peer-review validation | 4 / 10 | Preprint — not yet peer-reviewed. Hosted on a preprint server. |
| How recent | 5 / 5 | 2026 — within 1 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 | 0 / 3 | No effect size reported — scores zero (not stated in the record — scored 0) |
| 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 | No randomisation or blinding stated — scores zero (not stated in the record — scored 0) |
| Times cited | — / 7 | No citation count (not found in OpenAlex) — left out of this score |
| Citations per year | — / 5 | No citation count or no year — left out of this score |
| Impact for its field and year | — / 6 | No field-weighted citation impact (OpenAlex has none yet) — left out of this score |
| Cited by studies here | — / 6 | Not yet checked against this library's citation graph — left out of this score |
| Still being cited | — / 4 | No yearly citation counts — left out of this score |
| Senior author's track record | — / 4 | Senior author's record not available — left out of this score |
| Institution's track record | — / 3 | No institution listed in OpenAlex — left out of this score |
| Multi-centre collaboration | — / 3 | Institutions not listed — left out of this score |
| Indexed in PubMed | 1 / 2 | Not in PubMed, but has a DOI |
| Free to read | 0 / 2 | Behind a paywall — scores zero |
| Points | 15 / 62 | Scored on 12 of 20 parts. We have no data for the rest, so they are left out: 15 of the 62 points we could judge it on is 24 out of 100. |
| Total | 24 / 100 | Capped to 16 because this is not a peer-reviewed article. |
What each of these 20 components measures, and what this score is not →
Read the original
Free copy unknown: no free-copy check has an answer for this record yet. That does not mean it is paywalled.
Cite this study APA, Vancouver, BibTeX · download .bib or .ris
Built from the record alzhub holds for this paper, not looked up. Volume, issue and page numbers are not held in the record. The record's author list ends in “et al.”, so not every author is named. Check the citation against the original before you use it.
APA 7th
Jin, Z., Xu, K., Qi, M., Zhu, Q., Yang, B., Ferrada, G. A., et al. (2026). Carbonaceous Components Underlying Wildfire Smoke PM 2.5 -Associated Alzheimer’s Disease and Related Dementias in Older US Adults. medRxiv. https://doi.org/10.64898/2026.10.08.26364863
Vancouver
Jin Z, Xu K, Qi M, Zhu Q, Yang B, Ferrada GA, et al. Carbonaceous Components Underlying Wildfire Smoke PM 2.5 -Associated Alzheimer’s Disease and Related Dementias in Older US Adults. medRxiv. 2026. doi:10.64898/2026.10.08.26364863.
BibTeX
@article{jin2026-c7aa251b,
author = {Jin, Z. and Xu, K. and Qi, M. and Zhu, Q. and Yang, B. and Ferrada, G. A. and Fu, J. S. and Scovronick, N. and others},
title = {{Carbonaceous Components Underlying Wildfire Smoke PM 2.5 -Associated Alzheimer’s Disease and Related Dementias in Older US Adults}},
journal = {medRxiv},
year = {2026},
doi = {10.64898/2026.10.08.26364863},
url = {https://doi.org/10.64898/2026.10.08.26364863}
}