Summary: Living within roughly 50 meters of a major road or within 150 meters of a highway is associated with higher risks of dementia, Parkinson’s disease, Alzheimer’s disease and multiple sclerosis, likely driven by increased exposure to traffic-related air pollution. By contrast, proximity to green space appears to offer a protective effect against some of these neurological conditions.

Living Near Major Roads Linked to Higher Risk of Neurodegenerative Diseases

Source: University of British Columbia

New research published in the journal Environmental Health reports a population-level association between road proximity, traffic-related air pollution and higher incidence of several neurodegenerative disorders. The study, conducted by researchers at the University of British Columbia (UBC), analyzed health and environmental exposure data for approximately 678,000 adults living in Metro Vancouver.

Researchers estimated each participant’s residential exposure to road proximity, air pollution, noise and greenness (amount of surrounding vegetation) using postal code data from a baseline period (1994–1998) and a follow-up window (1999–2003). During follow-up the team identified 13,170 cases of non-Alzheimer’s dementia, 4,201 cases of Parkinson’s disease, 1,277 cases of Alzheimer’s disease and 658 cases of multiple sclerosis (MS).

Key Findings

• Living less than 50 meters from a major road, or less than 150 meters from a highway, was associated with increased incidence of non‑Alzheimer’s dementia and Parkinson’s disease. For non‑Alzheimer’s dementia, the hazard ratio for living near major roads was 1.14 (95% confidence interval 1.07–1.20).
• Air pollution measures — including fine particulate matter (PM2.5), black carbon and nitrogen dioxide (NO2) — were associated with higher incidence of Parkinson’s disease and non‑Alzheimer’s dementia. For Parkinson’s disease the hazard ratios per interquartile increase were approximately 1.09 for PM2.5, 1.03 for black carbon, and 1.12 for NO2.
• The study did not find clear associations between air pollution and the smaller case counts of Alzheimer’s disease or MS in Metro Vancouver, though the authors are analyzing larger Canada-wide datasets to investigate those outcomes further.
• Noise exposure showed no significant association with the outcomes evaluated in this cohort.
• Greater greenness around the home — that is, living closer to parks and vegetated areas — was associated with a reduced risk of Parkinson’s disease and non‑Alzheimer’s dementia, suggesting a protective effect.

Interpretation and Possible Mechanisms

The authors suggest that the observed associations may be driven in part by exposure to traffic-related air pollution. Inflammatory and oxidative stress pathways triggered by inhaled pollutants are plausible biological mechanisms that could increase the risk of neurodegenerative disease over time.

Importantly, when the researchers accounted for residential greenness, the adverse effects linked to air pollution were lessened. Greener neighbourhoods may encourage physical activity, increase opportunities for social interaction, lower stress, and even provide visual and psychological benefits that together could help protect cognitive and neurological health.

“For the first time, we have confirmed a link between air pollution and traffic proximity with a higher risk of dementia, Parkinson’s, Alzheimer’s and MS at the population level,” said Weiran Yuchi, the study’s lead author and a PhD candidate at the UBC School of Population and Public Health. “The good news is that green spaces appear to have some protective effects in reducing the risk of developing one or more of these disorders.”

Michael Brauer, the study’s senior author and a professor at the UBC School of Population and Public Health, emphasized urban planning implications: “These findings underscore the importance for city planners to incorporate greenery and parks into residential neighbourhoods and to consider strategies that reduce motor vehicle traffic.”

Study Design and Limitations

The study used administrative health records and environmental exposure estimates for adults aged 45 to 84 living in Metro Vancouver, assembled into a large cohort (N ~ 678,000). Cox proportional hazards models were used to assess associations for non‑Alzheimer’s dementia and Parkinson’s disease, while nested case‑control analyses addressed Alzheimer’s disease and multiple sclerosis where case counts were smaller.

Because Alzheimer’s disease and MS were less common in this population during the study period, the authors caution that statistical power was limited for those outcomes at the Metro Vancouver scale. They note ongoing analyses using larger national datasets to clarify whether the same air pollution links hold for Alzheimer’s disease and MS across Canada.

Conclusions

The Metro Vancouver study found that living very close to major roads and highways is associated with increased incidence of several neurodegenerative conditions, with evidence that traffic-related air pollution likely contributes to those associations. Noise was not shown to affect the outcomes in this analysis. By contrast, residential greenness was associated with lower risk for some neurological disorders, pointing to potential benefits of green infrastructure and accessible parks in urban planning to promote long‑term brain health.

Authors: Weiran Yuchi, Hind Sbihi, Hugh Davies, Lillian Tamburic & Michael Brauer (UBC School of Population and Public Health)

Source: University of British Columbia

Media Contact: Thandi Fletcher – University of British Columbia

Image Source: The image is in the public domain.

Original Research (open access): “Road proximity, air pollution, noise, green space and neurologic disease incidence: a population-based cohort study.” Environmental Health. DOI: 10.1186/s12940-020-0565-4