Research published in the Lancet journal found that dementia, a chronic disorder of mental processes, was more common in people who lived within 50 meters of a major road than those who lived further away.

The researchers tracked approximately 6.6 million adults aged between 20 and 85 in Ontario, Canada, for over a decade (2001 to 2012).

They relied on postal addresses to determine how close people lived to a road and analyzed medical records to see if they went on to develop dementia, Parkinson’s diseases or multiple sclerosis.

The results showed about one out of every 10 cases of dementia among those who lived next to a major road could be attributed to traffic exposure.

The risk is mostly associated with air pollution and traffic noise common in busy roads.

“Our study suggests that busy roads could be a source of environmental stressors that could give rise to the onset of dementia. Increasing population growth and urbanization has placed many people close to heavy traffic which could pose a large public health event,” said Dr Hong Chen, the lead author of the study.

Writing in a linked comment, Dr Lilian Calderón-Garcidueñas from the University of Montana said: “We must implement preventive measures now, rather than take reactive actions decades from now.”

Dementia is an umbrella term used to describe a group of conditions that affect how well our brains work.

The most common form of the ailment is Alzheimer’s disease. Symptoms include changes in memory, thinking, behavior, personality and emotions. These changes affect a person’s ability to perform everyday tasks and interfere with their everyday lives.