Living Near Major Roadways is Associated with Higher Incidence of Dementia

by | Sep 16, 2020 | 2017, Brain Health, Cognitive Health, Environmental Health, Pollution

Written by Angeline A. De Leon, Staff Writer. This study supports evidence that living near major roadways is associated with a higher incidence of dementia.

traffic jam on highwayEach year, an estimated 55 million individuals are diagnosed with some form of neurodegenerative disease such as dementia, Parkinson’s disease, or multiple sclerosis (MS) 1. Mounting evidence from toxicological research now suggests that environmental variables associated with traffic, particularly air pollutants like diesel exhaust, nitrogen oxides, and ultrafine particles, may contribute to the development of neurodegenerative disorders by increasing oxidative stress levels and inducing neuroinflammation 2-4. Even noise associated with high-traffic areas has been shown to play a role in cognitive impairment 5. Unsurprisingly then, studies now link traffic-related air pollution and noise to higher risk of Alzheimer’s disease and general cognitive diminishment 6. Neuroscience research suggests that traffic exposure may affect neurodegenerative processes, with evidence supporting a relationship between proximity to busy roads and changes in white matter volume and overall cognitive performance 7. In animals and humans with high levels of traffic exposure, the presence of ultrafine particles has even been detected in the frontal cortical regions of the brain 4. While the association between traffic exposure and dementia is relatively well supported, the relationships between traffic exposure and Parkinson’s disease and MS, two other major neurodegenerative diseases, are less clear. Thus, in a 2017 Lancet study 8, Canadian researchers evaluated the association between residential proximity to high-traffic areas and incidence of dementia, Parkinson’s disease, and MS.

A large population-based cohort study was conducted with a total of 6,537,988 individuals (aged 20 to 85 years) free of neurological disease and residing in Ontario, Canada for 5 years or longer (as of April 2001). Residential proximity to major roads was calculated based on individual postal-code address, and incident diagnoses of dementia, Parkinson’s disease, and MS were identified using public health administrative databases. Associations between proximity to high-traffic areas and incident cases of dementia, Parkinson’s, and MS were respectively calculated using Hazard Ratios (HRs), adjusting for potential risk factors for neurodegenerative pathology (age, sex, diabetes, brain injury).

After a follow-up period of about 11 years from the time of enrollment, a total of 243,611 cases of dementia, 31,577 cases of Parkinson’s disease, and 9,247 cases of MS were identified. Approximately half of all participants were identified as living within 200 miles of a major road, with 95% of participants living within 1000 miles of a major roadway. Living near a major road was associated with increased risk of dementia (but not Parkinson’s disease or MS): calculations yielded an adjusted HR of 1.07 for those living less than 50 miles (95% Confidence Interval: 1.06 to 1.08), 1.04 for those living 50-100 miles (95% CI: 1.02 to 1.05), 1.02 for those living 101-200 miles (95% CI: 1.01 to 1.03), and 1.00 for those living 201-300 miles (95% CI: 0.99 to 1.01), compared to those living more than 300 miles of a major road (Ptrend = 0.0349). The positive relationship between dementia and residing less than 50 miles of a major road was found to be stronger among participants who had lived in urban areas, those who previously lived in one of the six major cities, and those who had never moved (HR: 1.09-1.12).

Evidence from the study confirms an association between high traffic exposure and increased risk of dementia, with a more robust association specifically observed for residents having lived in major urban areas. Findings are in line with previous evidence suggesting a link between residential proximity to major roads and neurodegenerative pathology 6, 7.  However, null findings in regards to Parkinson’s disease and MS warrant further exploration. Future studies are also needed to illuminate the mechanisms through which traffic exposure influences neurocognitive function and to identify viable prophylactic strategies for urban dwellers. It should be noted that the current study did not account for use of medications which could potentially influence risk of dementia and that the assessment of traffic exposure based on postal code address has inherently limited precision. Nevertheless, this large cohort-based study provides valuable insight into the role of traffic exposure in the pathology of neurodegenerative disease.

Source: ChenH, Kwong JC, Copes R, et al. Living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis: a population-based cohort study. The Lancet. 2017; 389(10070): 718-726. DOI: 10.1016/S0140-6736(16)32399-6.

Posted September 16, 2020.

Angeline A. De Leon, MA, graduated from the University of Illinois at Urbana-Champaign in 2010, completing a bachelor’s degree in psychology, with a concentration in neuroscience. She received her master’s degree from The Ohio State University in 2013, where she studied clinical neuroscience within an integrative health program. Her specialized area of research involves the complementary use of neuroimaging and neuropsychology-based methodologies to examine how lifestyle factors, such as physical activity and meditation, can influence brain plasticity and enhance overall connectivity.

References:

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