Living near a main road could raise a person’s risk of dementia by 14%, research suggests.
Scientists from the University of British Columbia in Vancouver analysed around 678,000 adults who resided in the surrounding area.
They found those living less than 50m (164ft) from a main road or under 150m (492ft) from a highway were more likely to develop non-Alzheimer’s dementia within the next decade.
The scientists put this down to the higher rates of air pollution the patients were exposed to.
Living near a green space, like a park, may “protect” against the condition, they added.
Dementia is an “umbrella term” for a range of disorders associated with “an ongoing decline of brain functioning”, according to the NHS.
This can lead to memory loss, a decline in judgement or understanding, and reduced “sharpness”.
Dementia affects 850,000 people in the UK, Alzheimer’s Society statistics show.
Alzheimer’s is the most common form of the disease, impacting 62% of patients.
Dementia is poorly understood with no single cause.
Past research has linked “shorter residential distance to roads” to worse cognitive performance and a higher rate of “several neurological disorders”.
To learn more, the scientists looked at hundreds of thousands of adults who lived in Metro Vancouver between 1994 and 1998.
Metro Vancouver covers the metropolitan area of the town, including the city itself.
Using postcode data, the team estimated the participants’ “road proximity”, air pollution, noise exposure and “greenness”.
The participants were looked at again between 1999 and 2003.
Results, published in the journal Environmental Health, suggest living near a main road or highway increased the risk of developing non-Alzheimer’s dementia by 14%.
After Alzheimer’s, vascular dementia is the most common form of the disease in the UK, affecting 17% of patients.
This is caused by “reduced blood flow to the brain”, according to the NHS.
The results also suggest close proximity to a road raised the risk of Parkinson’s disease by 7%.
Exposure to air pollutants, including fine particulate matter (PM), may be to blame.
PM gets released from vehicle emissions and floats unseen in the atmosphere.
When smaller than 2.5μm (PM2.5), 400th of a millimetre, the particles are known to get “lodged” in the lungs.
The scientists also looked at Alzheimer’s and multiple sclerosis, however, due to “relatively low numbers in Metro Vancouver”, they could not be linked to road proximity.
The team are now analysing Canada-wide data in the hope of uncovering any risk.
After taking into account green space, the effects of air pollution were somewhat mitigated.
“The good news is green spaces appear to have some protective effects in reducing the risk of developing one or more of these disorders,” lead author Weiran Yuchi said.
“More research is needed, but our findings do suggest urban planning efforts to increase accessibility to green spaces and to reduce motor vehicle traffic would be beneficial for neurological health.”
Rather than green spaces just “reversing” air pollution, other factors may be at play.
“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,” study author Professor Michael Brauer said.
Exercise and staying “sharp” through socialising have both been linked to a reduced risk of dementia.
“There may even be benefits from just the visual aspects of vegetation,” Professor Brauer added.
The impact of noise was found to be “generally null”.
The scientists hope their results will encourage city planners to consider parks and other green spaces when developing residential areas.