Does Living by a Busy Road Boost Dementia Risk?

Exposure to heavy traffic tied to cognitive decline

Living near a high-traffic road may cause more mental health problems than just sleep deprivation, according to Canadian researchers.

In a population-based cohort in Ontario, dementia, but not Parkinson's disease or multiple sclerosis (MS), was more common in people who lived close to a major road than those who lived further away from the road, reported Hong Chen, MD, of Public Health Ontario in Canada, and colleagues.

Compared with people who lived at least 300 meters from a major roadway, those who lived 201-300 m (adjusted HR 1.00, 95% CI 0.99-1.01), 100-200 m (HR 1.02, 95% CI 1.01-1.03), 50-100 meters (HR 1.04, 95% CI 1.02-1.05), and less than 50 meters (HR 1.07, 95% CI 1.06-1.08) had an increase in incidence of dementia, they wrote online in the Lancet.

According to Chen, "increasing population growth and continuing urbanization globally has placed many people close to heavy traffic. With the widespread exposure to traffic and growing population with dementia, even a modest effect from near-road exposure can pose an enormous public health burden.

"Quantitatively speaking, our study estimated that 7%-11% of dementia cases in patients who live near major roads were attributable to traffic exposure alone," he explained to MedPage Today.

In an accompanying editorial, Lilian Calderón-Garcidueñas, MD, of the University of Montana in Missoula, and Rodolfo Villarreal-Ríos, of the Universidad del Valle de México in Mexico City, wrote that the study "opens up a crucial global health concern for millions of people."

Chen's group used Ontario's Registered Persons Database -- a registry of all residents who have ever had health insurance -- to determine the incidence of dementia, Parkinson's disease, and MS between 2001 and 2012. All participants were ages 20-85 years, Canadian-born, and Ontario residents for 5 years or longer as of April 1, 2001.

They separated the population into two cohorts -- individuals ages 20-50 with MS (n=4.4 million), and individuals ages 55–85 with dementia or Parkinson's disease (n=2.2 million) -- then excluded individuals with any of the three disorders at baseline.

Residential proximity to major roadways (thoroughfare with medium to large traffic capacity with controlled access and intersections) or highways (expressways and primary and secondary highways) was calculated according to six-character postal-code addresses from 1996.

The researchers assessed the associations between traffic proximity and the neurological conditions using Cox proportional hazards models, adjusting for individual and contextual factors such as diabetes, brain injury, and neighborhood income. They also conducted several sensitivity analyses, such as adjusting for access to neurologists and exposure to nitrogen dioxide and fine particulate matter.

They identified 243,611 cases of dementia, 31,577 cases of Parkinson's disease, and 9,247 cases of MS from 2001 to 2012.

The associations between proximity to major roadways and dementia risk were strongest among urban residents, especially those who lived in major cities (HR 1.12, 95% CI 1.10-1.14 for people living <50 m from a major traffic road) and who never moved (HR 1.12, 95% CI 1.10-1.14 for people living <50 m from a major traffic road).


Additionally, the researchers concluded that exposure to nitrogen dioxide and fine particulate matter was also linked to higher dementia incidence, but did not account for the full effect.

"Our study suggests that improvements in environmental health policies and land use planning aimed at reducing traffic exposure can have considerable potential for prevention of dementia, which would lead to a broad public health implication," Chen explained to MedPage Today.

He also suggested that changes in transportation emissions and land use policies may help to prevent dementia and improve public health.

The editorialists agreed that policy change is paramount to better health. "The health repercussions of living close to heavy traffic vary considerably among exposed populations, given that traffic includes exposures to complex mixtures of environmental insults ... We must implement preventive measures now, rather than take reactive actions decades from now," they wrote.

Study limitations included the inability to identify undiagnosed cases of the three conditions and the lack of information on medications that may influence risk of dementia.

Additionally, Chen's group noted that because air pollution exposure was estimated at the postal-code level, it may not account accurately for each individual's exposure.



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