SOURCE: Chen H, Kwong JC, Copes R, et al. Living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis: A population-based cohort study. Lancet 2017;389:718-726.

As we search for remediable explanations for Alzheimer’s disease and other dementias, several epidemiologically intriguing potential culprits have emerged, including air pollution and diesel exhaust. Although such pollutants have been shown to increase neuro-inflammation and oxidative stress, neither of these effects is sufficient evidence to definitively convict them.

Chen et al performed an analysis of new onset dementia cases (n = 243,611) in Canada to determine whether there was an association between how close one lives to a highway and incident dementia.

The adjusted hazard ratio indicated a slight increased risk for new onset dementia in people who lived < 50 meters from a major road (hazard ratio, 1.07) and a smaller, but still significant, increased risk among persons who lived 50-100 meters away (hazard ratio, 1.04). The relationship was strongest for persons who lived in major cities and lived in the same site long term.

Although it’s unlikely anyone anticipates that these 4-7% relative risk increases are dominant factors in the development of dementia, perhaps they can provide mechanistic clues to the disease.