June 4, 2021 -- Air pollution from the burning of fossil fuels may increase the risk of Parkinson’s disease, new research shows.
People who were exposed to the highest levels of nitrogen dioxide, commonly released by vehicles and power plants, were 40% more likely to have the disease, compared with people who had the lowest levels of exposure.
The study adds to growing evidence that exposure to pollutants and chemicals in the environment plays an important role in the development of Parkinson’s, a disease of the nervous system that makes people less able to control body movements.
Those findings might help explain the biological origins of the disease while also helping people avoid it, says Sun Ju Chung, MD, a professor in the Department of Neurology at the University of Ulsan College of Medicine in Seoul, South Korea, and lead author of the new study, which was published in the journal JAMA Neurology.
The new results show Parkinson’s disease as one of many health conditions associated with air pollution, Chung says.
"Air pollution is responsible for shortening people’s lives worldwide on a large scale, and the world is facing an air pollution pandemic," he says. "We need to reduce or avoid the exposure to [nitrogen dioxide] outdoors and indoors to reduce the risk of Parkinson’s disease."
About 15% of people who get Parkinson’s have a known family history, but not everyone with a genetic risk goes on to have the disease, says Ray Dorsey, MD, a neurologist at the University of Rochester Medical Center in New York, and co-author of the book Ending Parkinson's Disease. Pollution and environmental exposures have long been likely contributors.
Parkinson’s disease was first noted by British scientist James Parkinson in 1817. The Industrial Revolution was in full swing by then, and while a pollution-filled "London fog" often shrouded the city, Parkinson described a shuffling, shaking condition in six patients.
World's Fastest-Growing Brain Disease
Since then, Parkinson’s disease has become much more common -- now affecting 6 million people around the world. Each day, an average of about 200 people are diagnosed with the condition in the United States, Dorsey says. It is the world’s fastest-growing brain disease.
Since James Parkinson’s time, evidence that the environment has a role in the disease has only grown, Dorsey says. The disease is most prevalent in regions with high levels of air pollution, such as Europe and North America.
Rates are lowest in non-industrialized areas of Africa. And rates are growing fastest in parts of the world that are being developed quickly, such as China and India. Previous studies have also linked Parkinson’s with exposure to pesticides and industrial chemicals.
Still, establishing a definitive link between pollution and Parkinson’s has been challenging. Scientists can’t randomize people to live in polluted or non-polluted areas and then follow them for decades to see who gets which health conditions, Dorsey says.
It’s hard to get good data on who has been exposed to what, for how long, or in what combinations. The long lag between exposure and symptoms complicates things, too. Parkinson’s can also be challenging to identify and often goes undiagnosed. While some studies have suggested links between environmental exposures and the disease, others have shown no link.
To address some of the lingering questions, Chung and colleagues analyzed national health data on more than 78,000 people who lived in Seoul and were older than 40 between 2002 and 2006.
The database included addresses, which allowed the researchers to estimate each person’s exposure to six types of air pollutants based on historical information from nearby monitoring sites
Overall, the researchers found that 338 people got Parkinson’s disease within 9 years. People who had been exposed to the highest levels of nitrogen dioxide over a 5-year period were about 40% more likely to have the disease than were people with the lowest levels of exposure. The study found no link between the disease and five other pollutants, including ozone, particulate matter, and sulfur dioxide.
The findings add to growing evidence that things in the environment in general, and nitrogen dioxide specifically, contribute to Parkinson’s, says Dorsey, who joined two colleagues in writing an editorial about the new paper for the journal. A 2016 study in Denmark also linked exposure to traffic-related pollution with a higher risk of Parkinson’s.
Researchers are still looking into how pollution might cause Parkinson’s, but studies suggest that people often lose their sense of smell 10 to 20 years before they have the tremors and other classic symptoms of the disease, Dorsey says. Breathing in pollutants and chemicals may damage the olfactory system before the brain begins to decline.
Air pollution has been linked to other health conditions, such as stroke, cancer, and Alzheimer's disease, Dorsey says, and exposure to high levels of air pollution reduces lifespan by nearly 3 years worldwide. Understanding the links could help lead to policies that will protect people from a number of conditions, including Parkinson’s.
"We're trying to get the word out," he says, "because we think Parkinson's is, to a large extent, preventable."