For many years now, I have been reviewing studies of air pollution. Both Greenies and health advocates abhor it. But the research results are always disappointing. The ideal research result would be a demonstration that motor vehicle emissions give you cancer but there is no solid proof of that. Pollution repeatedly turns out to be peskily harmless. But no-one believes that. So they keep on doing studies to prove their point. One such is below. They hypothesize that air pollution sends you gaga.
Does it? It's another geography study. It tests your health according to where you live. It does NOT detect your personal exposure to air pollution. So that is a major flaw. But its conclusions are still amusing. They found no effect from most sources of pollution -- with one exception: Dust that farmers kick up when plowing etc. Avoid farms or lose your marbles!
As I said, the results are shaky anyway -- with their lack of personal data -- so I would not start demonizing farmers yet. The global warming folk demonize them enough already. And farm populations may be more prone to dementia anyway
I probably should note again why I think air pollution is so harmless: It is because human beings have been sitting around smoky campfires for about a million years. Over that time they have adapted to all the resultant pollution they inhale. Basically, they just cough it up. Looking at the big picture does help, doesn't it?
Comparison of Particulate Air Pollution From Different Emission Sources and Incident Dementia in the US
Boya Zhang et al
Question Are long-term exposures to particulate air pollution from different emission sources associated with incident dementia?
Findings In this nationally representative cohort study in the US, higher residential levels of fine particulate matter were associated with greater rates of incident dementia, especially for fine particulate matter generated by agriculture and wildfires.
Meaning These findings support the hypothesis that airborne particulate matter pollution is associated with the likelihood of developing dementia and suggest that selective interventions to reduce pollution exposure may decrease the life-long risk of dementia; however, more research is needed to confirm these relationships.
Importance Emerging evidence indicates that exposure to fine particulate matter (PM2.5) air pollution may increase dementia risk in older adults. Although this evidence suggests opportunities for intervention, little is known about the relative importance of PM2.5 from different emission sources.
Objective To examine associations of long-term exposure of total and source-specific PM2.5 with incident dementia in older adults.
Design, Setting, and Participants The Environmental Predictors of Cognitive Health and Aging study used biennial survey data from January 1, 1998, to December 31, 2016, for participants in the Health and Retirement Study, which is a nationally representative, population-based cohort study in the US. The present cohort study included all participants older than 50 years who were without dementia at baseline and had available exposure, outcome, and demographic data between 1998 and 2016 (N = 27 857). Analyses were performed from January 31 to May 1, 2022.
Exposures The 10-year mean total PM2.5 and PM2.5 from 9 emission sources at participant residences for each month during follow-up using spatiotemporal and chemical transport models.
Main Outcomes and Measures The main outcome was incident dementia as classified by a validated algorithm incorporating respondent-based cognitive testing and proxy respondent reports. Adjusted hazard ratios (HRs) were estimated for incident dementia per IQR of residential PM2.5 concentrations using time-varying, weighted Cox proportional hazards regression models with adjustment for the individual- and area-level risk factors.
Results Among 27 857 participants (mean [SD] age, 61  years; 15 747 [56.5%] female), 4105 (15%) developed dementia during a mean (SD) follow-up of 10.2 [5.6] years. Higher concentrations of total PM2.5 were associated with greater rates of incident dementia (HR, 1.08 per IQR; 95% CI, 1.01-1.17). In single pollutant models, PM2.5 from all sources, except dust, were associated with increased rates of dementia, with the strongest associations for agriculture, traffic, coal combustion, and wildfires. After control for PM2.5 from all other sources and copollutants, only PM2.5 from agriculture (HR, 1.13; 95% CI, 1.01-1.27) and wildfires (HR, 1.05; 95% CI, 1.02-1.08) were robustly associated with greater rates of dementia.
Conclusion and Relevance In this cohort study, higher residential PM2.5 levels, especially from agriculture and wildfires, were associated with higher rates of incident dementia, providing further evidence supporting PM2.5 reduction as a population-based approach to promote healthy cognitive aging. These findings also indicate that intervening on key emission sources might have value, although more research is needed to confirm these findings.