A massive long-term study in the US has found a clear link between air pollution and an increased risk of several neurodegenerative diseases that affect memory and cognitive ability, including Parkinson’s disease, Alzheimer’s disease, and other forms of dementia.
This relationship between smog and neurological disorders has been hinted at before, however, the new study published in The Lancet Planetary Health is notable for its scale and the finding that even levels of air pollution considered safe are still linked to an elevated risk of neurological disorders.
Scientists at the Harvard T H Chan School of Public Health, Emory University’s Rollins School of Public Health, and Columbia University’s Mailman School of Public Health tracked over 63 million older adults across the US from 2000 to 2017, looking at their rates of hospital admissions for several neurological disorders. They also kept tabs on how much air pollution each person was exposed to by looking at PM2.5 concentrations by zip code.
Particulate matter (PM) is a way of measuring levels of pollution in the air. PM2.5 is particulate matter in the air that's less than 2.5 micrometers in diameter, so particularly fine pollution like soot and ash that’s been coughed out by vehicle engines, fossil fuel plants, and the burning of fuels. Inhaling these particles is known to be linked to a number of health effects, namely associated with the cardiovascular system, as they’re small enough to enter the blood circulatory system. They are also known to have some link to brain atrophy and physical changes in the brain like the ones seen in Alzheimer’s.
After accounting for factors such as age, ethnicity, and socioeconomic status, the study found with each 5 microgram per cubic meter of air increase in annual PM2.5 concentrations, there was a 13 percent increased risk for first-time hospital admissions for Parkinson’s disease, Alzheimer’s disease, and related dementias. This risk remained elevated even when air pollution was below the safe levels of PM2.5 exposure set by the US Environmental Protection Agency (EPA) standards.
“Our US-wide study shows that the current standards are not protecting the aging American population enough, highlighting the need for stricter standards and policies that help further reduce PM2.5 concentrations and improve air quality overall,” Antonella Zanobetti, o-senior author of the study and principal research scientist in Harvard Chan School’s Department of Environmental Health, said in a statement.
They also found that women, white people, and urban-dwellers were at a heightened risk.
Some factors not measured by the researchers could have added to individuals' risk of developing neurological disorders. For example, the research did not track whether the participants smoked, which is a major risk factor for such diseases. That said, independent researchers not involved with the study have called the research “robust” and “useful,” noting the study’s conclusions remained valid and grounded, despite some of the study’s limitations.
“This research provides the most robust evidence to date that long term exposure to air pollutants may play a role in the deterioration of incurable conditions like Parkinson’s,” said Dr Beckie Port, Research Manager at Parkinson’s UK, who was not involved with the study, commenting on the findings.