The effect air and noise pollution can have on the development of neurodegenerative diseases is not fully understood, but results from a large study published in The Lancet suggest living close to heavy-traffic roadways could increase the risk of developing dementia — but not other neurological diseases, such as multiple sclerosis (MS) or Parkinson’s disease.
Heavy traffic — in addition to being noisy — can increase levels of nitrogen oxide, ultrafine particles, heavy metals, and volatile organic compounds in the air. Studies have shown that some of the pollutants impair cognitive function in animal models and alter brain structure.
“Living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis: a population-based cohort study” examined the role heavy-traffic exposure has in the development of dementia, Parkinson’s disease, and MS — three of the most common neurodegenerative diseases.
All adults with health insurance in Ontario, Canada, were enrolled in the study — covering nearly the entire population of 20- to 85-year-olds. Because each disease’s age onset is different, the researchers decided to separate the participants into two groups: the MS cohort, which included about 4.4 million individuals ages 20 to 50, and the dementia or Parkinson’s disease cohort, which was about 2.2 million people 55 and older.
None of the participants had a neurological disease at the beginning of the study.
Residential proximity to major roadways was the main factor the researchers evaluated. They determined the participants’ closeness based on postal-code information from 1996, five years before the study started.
Between 2001 and 2012, the researchers found, there were 243,611 cases of dementia, 31,577 cases of Parkinson’s disease, and 9,247 cases of MS. Dementia cases were more common in people who lived close to a major road (“close” being defined as 50 to 200 meters, or 164 to 656 feet) compared to those living farther than 300 meters, or 984 feet.
The association was confirmed by a detailed analysis of dementia cases among city residents. In those cases, people who lived as close as 50 meters to a major roadway had a 12%-increased risk of developing dementia.
Researchers said they could not find an association between road proximity and the incidence of Parkinson’s disease or MS, and as such concluded that the distance to a major road had no impact on the diseases’ development.