Abstract
BACKGROUND AND AIM: Evidence links air pollution to increased risk of dementia or Alzheimer’s disease (AD). However, previous studies have focused on hospitalizations as the measure of morbidity, which is a poor measure of either incidence or prevalence for these conditions. In addition, neuropathologic changes are known to occur many years prior to the diagnosis, and the relevant time window in which air pollution might increase risk of dementia or AD remains unclear. METHODS: We conducted a national, population-based, cohort study to investigate the impact of long-term exposure to PM2.5, NO2, and O3 on dementia and AD incidence, using the nationwide Medicare population and high-resolution air pollution data. To better approximate dementia and AD incidence, we used a 5-year “clean” period and all Medicare claims nationwide (2000-2018), including Medicare inpatient and outpatient claims, carrier file (primarily doctor visits), skilled nursing facility, and home health-care claims. Cox proportional hazard models were fit to estimate hazard ratios (HRs) for dementia and AD incidence. RESULTS:Using annual average pollutant level 5 years prior to diagnosis, per interquartile range (IQR) increase in annual PM2.5 (3.7 µg/m3), annual NO2 (13.3 ppb), and warm-season O3 (7.2 ppb), the HRs were 1.050 (95% CI: 1.045, 1.055), 1.017 (95% CI: 1.011, 1.023), and 0.994 (95% CI: 0.991, 0.998) for incident dementias, and 1.087 (95% CI: 1.078, 1.097), 1.045 (95% CI: 1.035, 1.056), and 0.972 (95% CI: 0.965, 0.978) for incident AD, respectively. For both outcomes there was strong evidence of linearity in concentration-response relationships for PM2.5 and NO2, suggesting that no safe threshold exists for health-harmful pollution levels. CONCLUSIONS:Using a large nationwide cohort, we provide strong evidence that exposure to PM2.5 and NO2, but not O3, were significantly associated with an increased incidence of dementia and AD. Improving air quality may yield substantial health benefits by reducing the burden of neurological disorders. KEYWORDS: Air pollution, Dementia, Alzheimer's disease, incidence
Highlights
We found elevated hazard ratios for both dementia and Alzheimer’s disease (AD) in relation to PM2.5, and less markedly to NO2, while hazard ratios for warm-season O3 were not elevated
For both PM2.5 and NO2, we found a larger effect on AD compared to dementia, which may reflect that fact that dementia includes a wide range of diseases with distinct etiologies, some of which may be unrelated to air pollution, while AD is a subset of dementia and a single disease, for which we found a stronger association
We found that shorter time windows between exposure (PM2.5 or NO2) and disease showed higher effect estimates, and we posit that it implies an acceleration of an existing process
Summary
Epidemiological evidence suggests air pollution exposure may increase risk of Alzheimer’s disease and related dementias (ADRD). Alzheimer’s disease (AD) contributes to about twothirds of dementia cases and is the sixth leading cause of death in the United States. Alzheimer’s disease (AD) contributes to about twothirds of dementia cases and is the sixth leading cause of death in the United States2 In response to this devastating public health threat, the National Alzheimer’s Project Act was signed into law to overcome dementia, and the National Plan was launched with Goal 1 aiming to prevent and effectively treat dementia (delay onset, slow progression) by 20253. A systematic review by Peters et al (2019), found 9 longitudinal studies of air pollution and Alzheimer’s disease and related dementias (ADRD). There have been several longitudinal studies since these reviews, with the majority finding positive associations between air pollutants and either dementia or AD6-14.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
