Image of heavy traffic on a highway

The closer you live to major roads, the higher the chances are that you’ll develop Alzheimer’s disease (AD), but traffic makes no difference to your risk for Parkinson’s disease (PD) or multiple sclerosis (MS).  What a remarkable statement!!  I love research of this kind; this is epidemiology at its best, so let me share some snippets from this project with you.

Start with a large geographic area, like Ontario, a province of Canada.  Take two massive samples.  For the multiple sclerosis group, try about 4.4 million people and get them before midlife (20-50 years of age); for the neurodegenerative disease cohort (AD & PD), take 2.2 million people but let them be older, between 55-85 years old.  Make sure they are all free of neurological disease and then track them for 11 years, counting the number of new cases (“incidence”) of AD, PD and MS.

This is just what Chen et al did, identifying 243,611 incident cases of AD, 31,577 cases of PD, and 9247 cases of MS.  Then, they related their data to proximity to major roads, adjusting for factors such as diabetes, brain injury, and income.

What did they Find?

Compared to people living more than 300 m from major roads, the adjusted hazard ratio (HR) for Alzheimer’s was 1.07 for people living less than 50 m from a major road, 1.04 for 50-100 m, 1.02 for 101-200 m, and 1.00 for 201-300 m.  So, risk drops 7 – 4 – 2 – 0 as we move away from the traffic; a gradient of specific disease defined by pollution! 

Now you need to ask yourself if it is time to move house.

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