Improving air quality can reduce risk for dementia, studies show
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Improving air quality can reduce the risk for dementia and improve cognitive function, according to multiple studies presented at the Alzheimer’s Association International Conference.
Previous research has shown that poorer air quality correlated with the development of brain plaques, but this is the first time that studies have suggested that reducing air pollution could lower the risk of all-cause dementia and Alzheimer’s disease.
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“These data demonstrate the importance of policies and action by federal and local governments, and businesses, that address reducing air pollutants,” Claire Sexton, DPhil, director of scientific programs and outreach at the Alzheimer’s Association, said in a press release.
Air quality improvement reduces dementia risk in older women
Xinhui Wang, PhD, an assistant professor of research neurology at the University of Southern California, and colleagues investigated whether older women who lived in areas with a greater reduction in air pollution experienced a slower decline in cognitive function and were less likely to develop dementia.
Specifically, they conducted three separate analyses of more than 2,000 women aged 74 to 92 years who were enrolled in the NIH-funded Women’s Health Initiative Memory Study-Epidemiology of Cognitive Health Outcomes (WHIMS-ECHO). None of the women had dementia at the beginning of the study. They were followed for a decade and completed cognitive function tests every year.
Overall, air quality greatly improved during the 10-year study period, the researchers found. Although cognitive function tended to decline among women as they aged, the risk for dementia for those living in areas with a greater reduction in fine particulate matter (PM2.5) and traffic-related pollutants (NO2) per 10% of the Environmental Protection Agency’s current standard over 10 years experienced 14% and 26% reductions in dementia risk. Their level of risk was similar to that seen in women aged 2 to 3 years younger, the researchers said.
The improvement in air quality also benefited women in terms of slower decline in overall cognitive function and memoryputting them par with women aged 1 to 2 years younger. It led to improvements in cognitive domains like working memory, episodic memory and attention/executive function. The association between improved air quality and reduced dementia risk did not substantially differ based on age, education, geographic region or whether the women had CVD.
“The possible benefits found in our studies extended across a variety of cognitive abilities, suggesting a positive impact on multiple underlying brain regions,” Wang said in the release.
Reduction in PM2.5 associated with reduced dementia risk in French adults
In a separate study presented at AAIC, Noemie Letellier, a postdoctoral scholar at the University of California, San Diego, and colleagues analyzed data from the French Three-City Study, a large cohort of more than 7,000 older adults. They wanted to quantify the impact of a reduction in PM2.5 on the incidence of dementia.
Like Wang and colleagues, they found that air quality had improved. Between 1990 and 2000, PM2.5 dropped a median of 12.2 g/m3. That improvement in air quality was associated with a 15% reduced risk for all-cause dementia (HR = 0.85; 95% CI, 0.76-0.95) and a 17% reduced risk for Alzheimer’s disease (HR = 0.83; 95% CI, 0.72-0.94). The findings held steady regardless of sociodemographic factors, health behaviors and APOE genotype.
Based on their results, the researchers estimated that approximately 197 fewer cases of all types of dementia per 100,000 people per year could be attributed to a reduction in PM2.5. In a hypothetical scenario in which PM2.5 was reduced by more than 13.1 g/m3, the rate difference was –0.33 (95% CI, –0.51 to –0.15).
“These data, for the first time, highlight the beneficial effects of reduced air pollution on the incidence of dementia in older adults. The findings have important implications to reinforce air quality standards to promote healthy aging,” Letellier said in the release. “In the context of climate change, massive urbanization and worldwide population aging, it is crucial to accurately evaluate the influence of air pollution change on incident dementia to identify and recommend effective prevention strategies.”
Effect of long-term air pollution on accumulation of brain plaques
In a cross-sectional study of participants in the Ginko Evaluation of Memory (GEM) Study, which is a longitudinal cohort of older U.S. adults who did not have dementia at baseline, researchers explored the role of long-term air pollution in the development of amyloid-beta a major culprit of Alzheimer’s disease, according to the Alzheimer’s Association.
Christina Park, a doctoral student in the department of epidemiology at the University of Washington, and colleagues examined associations between air pollution — specifically, levels of PM2.5, coarse particles (PM10) and NO2 — and the buildup of amyloid-beta peptide 1-40 (A1-40) in the plasma of more than 3,000 adults aged 75 years and older who were enrolled in the GEM study.
The researchers measured air pollution levels where the participants lived for up to 20 years before taking blood tests to measure A1-40. The study showed a strong association between long-term exposure to the three types of air pollutants and A1-40. For example, an increase in PM10 of 3 g/m3 over 10 years was associated with higher levels of A1-40 at baseline, with a percent difference of 1.8% (95% CI, 0.22%-3.4%), and similar associations were established between PM2.5 (interquartile range [IQR] = 2 g/m3) and NO2 (IQR = 7 ppb) and A1-40 in repeated analyses.
Park and colleagues noted that this is some of the first epidemiologic evidence showing that long-term exposure to these air pollutants is associated with increased amyloid-beta.
“Our findings suggest that air pollution may be an important factor in the development of dementia,” Park said in the release. “Many other factors that impact dementia are not changeable, but reductions in exposure to air pollution may be associated with a lower risk of dementia. More research is needed.”
References:
Alzheimer’s Association. Beta-amyloid and the amyloid hypothesis. https://www.alz.org/national/documents/topicsheet_betaamyloid.pdf. Accessed July 21, 2021.
Letellier N, et al. Association of air quality reduction with incident dementia: Effects of natural course and hypothetical air pollutant interventions using g-computation. Presented at: Alzheimer’s Association International Conference; July 26-30, 2021; Denver (hybrid meeting).
Park C, et al. Associations between long-term air pollution exposure and plasma amyloid beta in very old adults. Presented at: Alzheimer’s Association International Conference; July 26-30, 2021; Denver (hybrid meeting).
Wang X, et al. Association of air quality improvement with slower decline of cognitive function in older women. Presented at: Alzheimer’s Association International Conference; July 26-30, 2021; Denver (hybrid meeting).
Wang X, et al. Heterogeneous associations of air quality improvement with domain-specific cognitive function in older women. Presented at: Alzheimer’s Association International Conference; July 26-30, 2021; Denver (hybrid meeting).
Wang X, et al. Association of lower dementia risk with improved air quality in older women. Presented at: Alzheimer’s Association International Conference; July 26-30, 2021; Denver (hybrid meeting).
Perspective
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Rebecca M. Edelmayer, PhD
We’ve known for a long time that poor air quality or air pollution may lead to a greater risk for dementia, but this is the first time that we’re really seeing the suggestion that reducing pollution is associated with lowering risk of all-cause dementia and Alzheimer’s disease, and that’s been shown through two of the research studies, which looked at data across time — over 10 years — in a few populations around the world.
The implications for clinical practice are still to come. We’ve known for some time that air pollution is bad for our health overall, but it’s potentially also bad for our brains. These new data show that improving air quality may actually reduce the risk for dementia. It’s really important that we continue to think about policies and actions by local and federal governments that will help us address reducing air pollution. We still need to learn more, though. At this time, we don’t have all the information about how risk is distributed in all communities across the globe, but as we continue to learn more about this relationship between air quality and dementia risk, we can understand implications for all individuals that will eventually help us to drive towards more effective strategies for risk reduction — and that will certainly be brought into clinical care.
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