Parks and other green spaces in urban areas that might lower exposure to air pollutants did not affect a person's overall risk of developing MS, but can lessen the likelihood of other neurological diseases.
These findings were in the study "Road proximity, air pollution, noise, green space and neurologic disease incidence: a population-based cohort study," published in the journal Environmental Health.
The risk of neurological conditions like MS, non-Alzheimer's dementia (NAD), Parkinson's disease, and Alzheimer's disease increases with age, and is particularly high in people between 60 and 70 years old. As the population ages, the prevalence (proportion of people living with a disease at a given time) of these neurological ills is expected to rise.
Although certain lifestyle habits, such as smoking and physical activity, are seen to influence the risk of developing these conditions, it is not well known if other factors related to the people's surroundings can play a role too.
A team of researchers at The University of British Columbia (UBC), Canada, investigated a possible link between exposure to environmental factors like road proximity, air pollution, greenness and noise, and the risk of MS, NAD, Parkinson's, and Alzheimer's disease.
The team analyzed data covering about 678,000 people, ages 45 to 84, who had been living in Metro Vancouver between January 1994 and December 1998. Researchers investigated if environmental factors over this four-year exposure period influenced the development of any of these neurological conditions in these people.
They were then "followed" for another four years, from January 1999 to December 2003, and reported changes in their health noted.
Over these followup years, researchers identified 13,170 cases of NAD, 4,201 cases of Parkinson's disease, 1,277 cases of Alzheimer's disease, and 658 cases of MS.
Results showed that living close to a major road or highway - specifically, less than 50 meters (about 54 yards) away from a major road, or less than 150 meters (about 164 yards) away from a highway - was linked to a higher incidence (rate of new disease cases over a given time) of all the neurological conditions studied, including MS.
Air pollution exposure increased the risk of NAD and Parkinson's disease, the study reported. Because of the low number of Alzheimer's and MS cases in the group analyzed, researchers were unable to identify an association between these two conditions and air pollution. A larger cohort (study group) is needed to draw conclusions here, they said.
Data, however, suggested that the presence of fine particulate matter (PM2.5, produced by combustion) may contribute to the risk of MS.
Living close to green spaces within cities lowered the incidence of NAD and Parkinson's, but not of MS. Researchers speculated that this could be because of limits on data in their statistical model.
Noise from nearby major roadways also was not seen to affect the risk of developing any of the conditions studied.
"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," Weiran Yuchi, the study's lead author, said in a UBC press release.
"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," Yuchi added. "More research is needed, but our findings do suggest that urban planning efforts to increase accessibility to green spaces and to reduce motor vehicle traffic would be beneficial for neurological health."
The team believes that the findings underscore the importance of city planning, and support the incorporation of greenery and parks.
"For people who are exposed to a higher level of green space, they are more likely to be physically active and may also have more social interactions. There may even be benefits from just the visual aspects of vegetation," said Michael Brauer, the study's senior author.
"Given the high proportion of the population living in proximity to traffic ... and the growing prevalence of neurological disorders, future studies in other urban areas which address potential joint effects of multiple environmental exposures are warranted," the team concluded.
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