May 22 (UPI) -- City-dwellers are nearly 30 percent more likely to be diagnosed with multiple sclerosis than those living in more rural areas, a study presented Friday at the European Academy of Neurology Virtual Congress has found.
Based on the results, which will also be published in European Journal of Neurology, air pollution could be a risk factor for the development of the disease, according to the authors, who conducted their research in Italy.
"It is well recognized that immune diseases such as MS are associated with multiple factors, both genetic and environmental," co-author Dr. Roberto Bergamaschi, of the IRCCS Mondino Foundation in Pavia, Italy, said in a statement.
"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.
MS affects roughly 1 million Americans, according to estimates from the National MS Society. Research has determined that it is an autoimmune disorder in which the immune system attacks the protective sheath that covers the nerve fibers in the spinal cord, disrupting communication between the brain and the rest of the body.
The vast majority of people with the disease have the relapsing-remitting, which is characterized by symptom "flares" or attacks. The disease most often is diagnosed in adults between 20 and 40 years old, and is more common in women.
Symptoms vary in severity daily and can include fatigue, walking difficulty, numbness, pain and muscle spasms.
For their study, Bergamaschi and his colleagues reviewed data on more than 900 people with MS in the Lombardy region of northwestern Italy. The area is home to nearly 550,000 people.
In general, MS rates in the region have increased 10-fold in the past 50 years, from 16 cases per 100,000 residents in 1974 to almost 170 cases per 100,000 residents in 2020, the researchers found. In addition, they compared three different areas within the region based on their levels of "urbanization."
Two of the areas were found to be above the European Commission's threshold for air pollution as determined by levels of pollutants known as particulate matter, or PM, a term used to describe a mixture of solid particles and droplets in the air.
PM is divided into two categories: PM10, which includes particles with a diameter of 10 micrometers or smaller, and PM2.5, which includes particles with a diameter of 2.5 micrometers or smaller.
Both PM10 and PM2.5 are major pollutants and known to be linked to various health conditions, including heart and lung disease, cancer and respiratory problems, according to the World Health Organization.
The researchers observed that those who live in rural areas, where lower levels of both types of PM existed, had a reduced risk for MS. Meanwhile, those living in urban areas, with more PM in the air, had a 29 percent higher risk for the disease.
The authors emphasized that they conducted their study in winter, when air pollutant concentrations are highest.
"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 the higher risk areas, we are now carrying out specific analytical studies to examine multiple environmental factors possibly related to the heterogeneous distribution of MS risk."