DEMENTIA IS MORE common in people who live within 50 metres of a major road than those who live further away, according to a study looking at 6.6 million people published in The Lancet today.

However, the study found no link between traffic exposure and Parkinson’s disease or multiple sclerosis.

The observational study estimated that up to one in 10 (7-11%) cases of dementia among those who live within 50 metres of a major road could be attributable to traffic exposure. While previous research had suggested air pollution and traffic noise can contribute to the degradation of a brain, the paper is the first to investigate the link between living close to heavy traffic and the onset of major neurodegenerative diseases.

The researchers tracked all adults aged between 20 and 85 living in Ontario, Canada – approximately 6.6 million people – for over a decade from 2001 to 2012. They used postcodes to determine how close people lived to a road and analysed medical records to see if they went on to develop dementia, Parkinson’s disease or multiple sclerosis.

Almost all people (95%) in the study lived within one kilometre of a major road and half lived within 200 metres of one. Over the study period, more than 243,000 people developed dementia, 31,500 people developed Parkinson’s disease and 9,250 people developed multiple sclerosis.

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 of developing dementia reduced as people lived further away from a main road – with a 7% higher risk in developing dementia among those living within 50 metres, a 4% higher risk at 50-100 metres, a 2% higher risk at 101-200 metres and no increase in risk in those living more than 200 metres away.

The study estimated air pollution exposure based on postcode, so does not account for each individual’s exposure.

Because the study is observational it cannot establish causality, but the study was designed to control for socioeconomic status, education levels, BMI and smoking meaning the link is unlikely to be explained by these factors.

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