Poor air quality is linked to the risk of Parkinson's disease, according to a new study. People who live in areas with high levels of air pollution are at 56% higher risk of developing the condition compared to those living in regions with better air quality.

Parkinson's disease is a progressive brain disorder marked by uncontrollable movements such as tremors, muscle stiffness and issues with balance and coordination. As the disease progresses, the patients may develop sleep problems, depression, memory difficulties, fatigue and may lose the ability to walk and talk.

This condition occurs from the death or impairment of neurons in the brain, the specific cause of which remains unknown. Researchers believe a combination of genetic and environmental factors, such as exposure to toxins, can be factors.

"Previous studies have shown fine particulate matter to cause inflammation in the brain, a known mechanism by which Parkinson's disease could develop. Using state-of-the-art geospatial analytical techniques, we were, for the first time, able to confirm a strong nationwide association between incident Parkinson's disease and fine particulate matter in the U.S.," said lead researcher Brittany Krzyzanowski, from Barrow Neurological Institute.

Researchers observed that the relationship between air pollution and Parkinson's disease is not the same in every part of the country. The difference is believed to be due to the changes in the composition of the particulate matter.

"Regional differences in Parkinson's disease might reflect regional differences in the composition of the particulate matter. Some areas may have particulate matter containing more toxic components compared to other areas," Krzyzanowski said.

The team identified nearly 90,000 people with Parkinson's disease from a Medicare dataset of around 22 million. Those with Parkinson's disease were geocoded to the neighborhood of residence to calculate the rates of Parkinson's disease in each region. The air pollution in these regions was measured in terms of average annual concentrations of fine particulate matter.

After adjusting other risk factors, such as age, sex, race and smoking history, the team identified a link between an individual's exposure to fine particulate matter and the risk of developing Parkinson's disease later.

"The Mississippi-Ohio River Valley was identified as a Parkinson's disease hotspot, along with central North Dakota, parts of Texas, Kansas, eastern Michigan and the tip of Florida. People living in the western half of the U.S. are at a reduced risk of developing Parkinson's disease compared with the rest of the nation," the researchers said in a news release.

The study has not delved into the different sources of air pollution, however, Krzyzanowski believes high road network density and industrialization make the Mississippi-Ohio River Valley a hotspot. "This means that the pollution in these areas may contain more combustion particles from traffic and heavy metals from manufacturing which have been linked to cell death in the part of the brain involved in Parkinson's disease," they said.

The researchers hope the findings will help bring stricter policies to cut down air pollution and decrease the risk of Parkinson's disease.