An eyebrow-raising study contends living along or near a major road or highway might be linked to a higher incidence of Alzheimer's disease, dementia (which is mostly triggered by Alzheimer's), Parkinson's disease and multiple sclerosis (MS).

The study from the University of British Columbia (UBC), ranked among the top three universities in Canada, found living fewer than 50 meters from a major road, or less than 150 meters from a highway, is associated with a higher risk of developing neurological disorders. The study, published in the journal Environmental Health, said this outcome was likely due to the increased exposure to air pollution and the toxins such as carbon monoxide and microscopic particulate matter (PM) it contains.

"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, study lead author from UBC, said.

The study saw researchers analyze data of 678,000 adults between the ages of 45 and 84 that lived in Metro Vancouver from 1994 to 1998, and during a follow-up period from 1999 to 2003. Using postal code data, it estimated individual exposures to road proximity, air pollution, noise and "greenness" at each person's residence. The follow-up period saw researchers identify 13,170 cases of non-Alzheimer's dementia, 1,277 cases of Alzheimer's disease, 4,201 cases of Parkinson's disease and 658 cases of MS.

Especially for non-Alzheimer's dementia and Parkinson's disease, living near major roads or a highway was associated with 14 percent and 7 percent increased risk of both conditions, respectively. The presence of trees, plants and green space seem to mitigate the effects of air pollution on the neurological disorders, however. Researchers believe this protective effect might be due to several factors.

"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," Michael Brauer, study senior author, added. "There may even be benefits from just the visual aspects of vegetation."

The findings are surprising because they depart substantially from what’s accepted as the major causes of dementia. Among the most common causes of irreversible dementia are degenerative neurological diseases such as Alzheimer's, Parkinson's and Huntington's, all of which worsen over time, traumatic brain injuries caused by car accidents and falls, infections of the central nervous system (CNS) such as meningitis and HIV, and vascular disorders that affect the blood circulation in a person's brain. Long-time alcohol or drug use is an accepted cause of dementia.

Causes of dementia that might be reversible include tumors, subdural hematomas (blood clots beneath the outer covering of the brain), metabolic disorders such as a vitamin B12 deficiency, low blood sugar or hypoglycemia, normal-pressure hydrocephalus (a buildup of fluid in the brain) and hypothyroidism or a low level of thyroid hormones.

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Air pollution may increase kids' risk for diabetes. REUTERS/Susana Vera