Canadian experts found that one in ten cases of dementia among people living within 50 metres of busy road could be attributable to traffic exposure, after examining the medical records of 6.6 million adults for more than a decade.
Previous research has suggested that air pollution and traffic noise may contribute to neurodegeration, although the study in The Lancet is the first to look at the impact of living close to busy roads.
The authors cautioned that the increase was very small but added to a growing body of evidence around possible links between environmental factors and the disease.
Lead author Dr Hong Chen, of Public Health Ontario, said: “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 urbanisation has placed many people close to heavy traffic, and with widespread exposure to traffic and growing rates of dementia, even a modest effect from near-road exposure could pose a large public health burden.”
The team used postcodes and medical records to track all adults aged between 20 and 85 living in Ontario between 2001 and 2012.
While there was no association between living near a road and Parkinson’s disease or multiple sclerosis, dementia was more common the closer people lived to busy roads.
The risk fell the further people lived from a main road, with a 7 per cent higher risk in developing dementia among those living within 50m, compared to no increase in risk in those living more than 200m away.
Prof Martin Rossor, director for dementia research at University College London Hospitals, said: “Whilst this study does not provide sufficient reason to drive individual choices, if available, it is an important public health message on the dangers of air pollution and the contribution of the built environment in responding to the dementia challenge.”
Dr David Reynolds, chief scientific officer at Alzheimer’s Research UK, added: “Conditions like dementia have multiple risk factors including age and genetics, and other social factors relating to where people live in cities could also be playing a part here.”