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It is well known that living in a highly polluted environment has negative effects on your respiratory health. Disorders such as asthma, flare up of bronchitis and cancer are all associated with living in a large city with lots of traffic and factories. It isn’t just bad for those with preexisting conditions. If you look at a cadaver of a physically active life-long Londoner you’ll easily mistake them for a heavy smoker. The matter is quite pressing; according to the WHO 7 million people per year die prematurely as a consequence of air pollution.
As a consequence there has been significant global press coverage over recent years seeking change in policy and city planning in countries about the world. This has largely been based on the well documented respiratory complications. However there has been growing concerns about the impact on the nervous system namely neurodegenerative disorders. A study in the Lancet has shown that perhaps we should be more concerned.
The population based cohort study, based in Canada, retrospectively analysed living proximity to major roadways and your risk of developing neurodegenerative disorders such as Parkinson’s Disease (PD), Alzheimer’s Dementia (AD) or Multiple Sclerosis (MS). This was a massive study and really is proof of concept for big data and health analytics.
Due to the scope of the study and the differing epidemiology of the disorders investigated the total number if participants was divided in two. Adults aged 20-50 were in the MS cohort (~4.4 million) and 55-85 years of age were in the PD and AD cohort (~2.2 million). By tracking postal addressed over a decade alongside and monitoring diagnoses through administrative databases over time the team were able to monitor living distances to road and diagnoses of the participants.
A decade is a long time and to specifically attribute a single factor to something is incredibly complex. Due to a statistical analysis method (as explained in this article) the team were able to adjust their results to take into account factors such as BMI, heart rate, access to neurologists, physical activity and frailty.
In summary the results show that there was no link between proximity to major roadways and %risk of developing MS or PD however the same cannot be said for Alzheimer’s Dementia.
Living near roadways was positively correlated with an increased Alzheimer’s Dementia incidence with 7-11% of dementia cases being attributed to traffic exposure. The relationship was strongest in those who never moved away from the roadside and were living within 50m of a major roadway.
This could ultimately be down to the exposure of nitrogen oxides, ultrafine particles, fine particulate matter (≤2·5 μm in diameter or PM₂·₅), heavy metals, polycyclic aromatic hydrocarbons, volatile organic compounds, noise, and other factors. This certainly no reason to panic however city planning and global health policy will need to consider these results in the future.
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