People who live close to high-traffic roadways face a higher risk of developing dementia than those who live further away, according to a new study from Public Health Ontario (PHO) and the Institute for Clinical Evaluative Sciences (ICES).
The study, published in the medical journal The Lancet, found that people who lived within 50 meters of high-traffic roads had a 7% higher likelihood of developing dementia compared to those who lived more than 300 meters away from busy roads. The increase in the risk of developing dementia went down to 4% if people lived 50-100 meters from major traffic, and to 2% if they lived within 101-200 meters. At more than 200 meters, there was no elevated risk of dementia.
Increasing population growth and continuing urbanisation 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. This 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. This study adds weight to previous observations suggesting that roadway traffic is an important source of environmental stressors that could give rise to neurological disorders and that future investigation targeting the effects of different aspects of traffic such as traffic-related air pollutants and noise on neurological health is merited.—Chen et al.
The researchers examined records of more than 6.5 million Ontario residents aged 20-85 to investigate the correlation between living close to major roads and dementia, Parkinson’s disease and multiple sclerosis. They assembled two population-based cohorts including all adults aged 20–50 years (about 4.4 million; multiple sclerosis cohort) and all adults aged 55–85 years (about 2.2 million; dementia or Parkinson’s disease cohort) who resided in Ontario, Canada on 1 April 2001.
Incident diagnoses of dementia, Parkinson’s disease, and multiple sclerosis were ascertained from provincial health administrative databases with validated algorithms. The researchers identified 243,611 cases of dementia, 31,577 cases of Parkinson’s disease, and 9,247 cases of multiple sclerosis in Ontario between 2001 and 2012. In addition, they mapped individuals’ proximity to major roadways using the postal code of their residence. The findings indicate that living close to major roads increased the risk of developing dementia, but not Parkinson’s disease or multiple sclerosis, two other major neurological disorders.
Little is known in current research about how to reduce the risk of dementia. Our findings show the closer you live to roads with heavy day-to-day traffic, the greater the risk of developing dementia. With our widespread exposure to traffic and the greater tendency for people to live in cities these days, this has serious public health implications.—Dr. Hong Chen, lead author
The study is the first in Canada to suggest that pollutants from heavy, day-to-day traffic are linked to dementia, said co-author Dr. Ray Copes, chief of environmental and occupational health at PHO. Previous research that air pollutants can get into the blood stream and lead to inflammation, linked with cardiovascular disease and possibly other conditions such as diabetes. The new study suggests air pollutants that can get into the brain via the blood stream can lead to neurological problems, Copes added.
As urban centers become more densely populated and more congested with vehicles on major roads, Dr. Copes suggests the findings of this paper could be used to help inform municipal land use decisions as well as building design to take into account air pollution factors and the impact on residents.
Chen, Hong et al. (2017) “Living near major roads and the incidence of dementia, Parkinson's disease, and multiple sclerosis: a population-based cohort study” The Lancet doi: 10.1016/S0140-6736(16)32399-6