New research finds a marked increase in dementia among those living by busy roadways.
The highways around where I live in Portland, Oregon are like congestion voids—black holes or boundless oceans. You go in hoping to reappear elsewhere in the city or beyond, but without any assurance of exiting at all; time and space cease to have any meaning as waves and waves of Subarus roll toward the horizon. As once-plentiful provisions of Planet Money podcasts dwindle, you can feel madness setting in.
As it turns out, being around traffic for extended periods of time may have a very real effect on the human brain. This is according to Health Canada-funded research published this month in the Lancet that looked at the neurological health of two large-scale populations living in Ontario consisting of several million adults each. The study found that those individuals living closest to busy highways suffered from significantly increased rates of dementia, a symptom of irreversible neurodegeneration.
Specifically, the study found that up to one in 10 cases of dementia could be attributed to traffic exposure. This backs up earlier research finding that living near roadways—and the associated air pollution—can be tied to "insidious effects on structural brain aging."
The Health Canada study looked at all adults aged between 20 and 85 living in Ontario, a population of about 6.6 million people. It used postal codes to determine proximity to roadways and health records to determine incidence of dementia, Parkinson's disease, or multiple sclerosis. No correlation was found between the latter two afflictions and living around traffic.
Dementia risk, however, did vary with proximity to busy roadways. Those living within 50 meters of a busy road were about 7 percent more likely to develop dementia. At 50 to 100 meters, the increase went down to about 4 percent, while 100 to 200 meters led to a 2 percent increase. At greater distances, no significant increase was found.
By controlling for two common air pollutants—nitrogen dioxide and fine particulate matter—the researchers were able to negate some but not all of the increased risk. This points to the likelihood that the increased dementia risk is due to a combination of factors, possibly including the increased noise levels found around traffic.
The study controlled for complicating factors like socioeconomic status, education levels, BMI, and smoking, but as an observational study—where the variable of interest isn't under the direct control of the researchers—it can't make strict claims of causality. Still, given the above controls, it's hard to imagine what else the culprit could be.
So, what we're facing is a major public health concern. In a separate Lancet commentary, Lilian Calderón-Garcidueñas, a researcher at the University of Montana studying the neurological effects of air pollution, offers this conclusion: "the robust observation of dementia involving predominantly urban versus rural residents, opens up a crucial global health concern for millions of people... The health repercussions of living close to heavy traffic vary considerably among exposed populations, given that traffic includes exposures to complex mixtures of environmental insults..."
"We must implement preventive measures now, rather than take reactive actions decades from now."