Exposure to air pollutants, particularly to fine particle pollutants (2.5 micrometers or less in diameter), seems to increase a person’s risk of multiple sclerosis (MS), a study from northern Italy suggests.
It found that people living in urban, more polluted areas have a 16% higher relative risk of developing this disease than do people in rural areas.
These findings were disclosed at the 2020 European Academy of Neurology (EAN) Congress — held virtually due to the COVIV-19 pandemic — in the oral presentation “PM2.5 exposure is a risk factor of multiple sclerosis. An ecological study with a Bayesian mapping approach” (registration at EAN is needed to access its studies).
Many environmental factors are known to act as triggers of the damaging immune response seen in MS patients. Those most well-studied include cigarette smoking, diet, and levels of vitamin D. But exposure to air pollutants has also been suggested as a risk factor.
Professor Roberto Bergamaschi and his team at the Instituto Neurologico Nazionale a Carattere Scientifico (IRCCS) examined the exposure to air pollutants among a group of 927 MS patients in northern Italy.
Patients were from the province of Pavia, which includes 188 municipalities, and were specifically examined for their exposure to fine particulate matter smaller than 2.5 micrometers in diameter (known as PM2.5).
These particles are a mixture of solid and liquid matter suspended in air, that arise mainly from household and commercial heating, industrial activities, roadway vehicles, and agriculture. The analysis was conducted during the winter, which is when pollutant concentrations reach higher levels.
The team noted that Pavia could be divided into three separate air pollution zones, with the northern region — which borders the urbanized Milan area — having the highest seasonal levels of PM2.5, with concentrations progressively decreasing as you move south. Cases of MS also appeared to be less common in this province’s southern region.
After adjusting for confounding factors like age, urbanization degree, and deprivation index — which assesses educational levels, employment, percentage occupied, single-parent families, and housing density in each region — the researchers investigated the association between PM2.5 levels and MS prevalence.
People living in areas with low levels of PM2.5 pollutants had a low MS risk, a statistical analysis found. When accounting for PM2.5 levels, people residing in urban regions were 16% more likely to develop MS — a relative risk ratio of 1.16, which means a 16% increase compared with those living in rural areas (who have a relative risk ratio as low as 0.8).
Compared to no risk at all, the MS risk rose in total by almost 29% for people residing in more urbanized areas of Pavia province.
Bergamaschi also noted that the prevalence of MS in this population was 169 per 100,000 inhabitants, which is 10 times higher than that seen in data collected almost 50 years ago on the same area — 16 cases per 100,000 inhabitants in 1974.
While this jump in prevalence may be due to better survival rates among MS patients, a rise in pollution across recent decades may also be a contributor.
“It is well recognised that immune diseases such as MS are associated with multiple factors, both genetic and environmental. Some environmental factors, such as vitamin D levels and smoking habits, have been extensively studied, yet few studies have focused on air pollutants,” Bergamaschi said in a press release.
“We believe that air pollution interacts through several mechanisms in the development of MS and the results of this study strengthen that hypothesis,” he added.
The researchers noted some limitations to their work, such as the lack of data regarding duration of exposure to air pollutants, and the failure to control for other factors, such as cigarette smoking, diet, genetic factors, and exposure to other pollutants.
“Nevertheless, our findings highlighted that air pollution could be one of the risk factors for MS, and thus it should be in the future analyzed together with other already known risk factors,” Bergamaschi said in the presentation.
Researchers are continuing to examine areas with higher MS risk, looking at various environmental factors that could influence this risk.
