Air pollution, infamous for causing health conditions like stroke, heart disease, cancer, asthma, and respiratory diseases, is an issue that plagues both low- and high-income countries alike. Its impact is far-reaching, with the World Health Organization (WHO) stating that an astounding 99% of the global population resides in regions not meeting WHO air quality guidelines.
Air pollution primarily comprises byproducts from combustible fuels used in automobiles, power plants, and various industries. Areas with high levels of air pollution often expose people to too much fine particulate matter. This is a type of harmful pollution composed of tiny particles linked to cardiovascular diseases, respiratory disorders, and cancers.
A recently published paper in the Journal of Alzheimer’s Disease reveals ambient air pollution as a potential dementia risk factor. Unlike most studies, which focus on populations aged 65 and above, this research targets middle-aged individuals who could gain the most from early interventions.
The Study at a Glance
The authors enrolled participants from The Vietnam Era Twin Study of Aging (VETSA). This dataset is a national registry of male twins who served in the United States military between 1965 and 1975, aged 50-59 at the start of the study.
At the study’s outset and again about 10-15 years later, participants underwent comprehensive neuropsychological testing, completed self-report questionnaires, provided medical history, and participated in interviews. The neurological assessments measured aspects related to dementia, such as episodic memory, executive function, processing speed, and verbal fluency.
To evaluate air quality, the authors associated each participant’s historical address information with data on fine particulate matter and NO2 levels in different geographical areas from 1993 to 2017. They used this information to estimate each participant’s past and recent exposure to air pollution.
Additionally, the study explored the potential moderating effect of genetic modifications. They especially focused on an APOE variant known to influence Alzheimer’s disease. At the initial assessment, the authors collected participants’ blood and genotyped the samples to determine the presence of these variants.
As expected, cognitive abilities tended to decline with age. The authors observed that exposure to higher levels of fine particulate matter corresponded with poorer verbal fluency scores.
They saw more dramatic variations in individuals with the APOE variant. That is, those exposed to high levels of fine particulate matter, either recently or in the past, and who carried the variant, showed worse cognitive performance. Conversely, APOE variant carriers exposed to lower levels demonstrated better performance.
Interestingly, individuals with the APOE variant who experienced higher NO2 levels showed better cognitive outcomes. This result contrasts with the effects observed for fine particulate matter exposure. It suggests that the influence of the APOE genotype on cognitive functioning may vary depending on environmental factors, like pollution.
While the study controlled for variables such as urban/rural location, education, and income, undetermined demographic factors may have influenced the results. It’s important to note that participants were predominantly non-Hispanic White males, most residing in rural areas. Also, the authors only collected pollution data from residential addresses, meaning they did not consider work-related exposure. In addition, the study did not include other biological mechanisms that could influence the relationship between air pollution and age-related cognition.
Results highlight the complexity of genes in disease analyses and show that APOE variants alter the effects of environmental factors. Thus air pollution emerges as a modifiable risk factor that, if managed, could benefit those at risk for cognitive disorders. Considering the widespread presence of pollutants globally, these findings could benefit many people.
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Franz CE, Gustavson DE, Elman JA, Fennema-Notestine C, Hagler DJ Jr, Baraff A, Tu XM, Wu TC, De Anda J, Beck A, Kaufman JD, Whitsel N, Finch CE, Chen JC, Lyons MJ, Kremen WS. Associations Between Ambient Air Pollution and Cognitive Abilities from Midlife to Early Old Age: Modification by APOE Genotype. J Alzheimers Dis. 2023;93(1):193-209. doi: 10.3233/JAD-221054. PMID: 36970897.