By Sally Robertson, BSc
People living within 50 meters of a busy road are at an increased risk of developing dementia, compared with people who live further away, according to research published in The Lancet.
The study also analyzed the link between traffic pollution exposure and the risk of Parkinson’s disease or multiple sclerosis, but found no association for these two conditions.
Previous studies have suggested that living close to major roads may negatively affect cognition. However, little is known about how this may be linked to the incidence of dementia, Parkinson’s disease or multiple sclerosis and the current study is the first to investigate these relationships.
Our study suggests that busy roads could be a source of environmental stressors that could give rise to the onset of dementia… with widespread exposure to traffic and growing rates of dementia, even a modest effect from near-road exposure could pose a large public health burden.”
Lead author of the research Dr. Hong Chen (Public Health Ontario, Canada).
For the study, Chen and team tracked the medical records and post codes of all adults, aged between 20 and 85 years, living in Ontario, Canada (approximately 6.6 million people), from 2001 to 2012. Almost all of the people studied (95%) lived within one kilometer of a busy road and half lived within 200 meters.
Over the study period, the team identified 243,611 cases of dementia; 31,577 cases of Parkinson’s disease and 9,247 cases of multiple sclerosis.
The researchers found no association between living near a road and the incidence of Parkinson’s or multiple sclerosis. However, they did find the incidence of dementia rose, the closer people lived to busy roads. Compared with people who lived further than 300 meters away from a major traffic road, the risk of dementia was 7% higher among those whole lived less than 50 meters away, 4% higher for those living 50–100 meters away and 2% for those living 101–200 meters away. No increase was observed for those living between 201 and 300 meters away.
Since the study was observational, causality could not be established, but external factors such as socioeconomic status, education level, BMI, diabetes and brain injury were adjusted for, meaning the link is unlikely to be accounted for by these factors.
Commenting on the study, Professor of old age psychiatry, Rob Howard (University college London) said: “Regardless of the route of causation, the study presents one more important reason why we must clean up the air in our cities.”
“More research to understand this link is needed, particularly into the effects of different aspects of traffic, such as air pollutants and noise,” concludes Chen.