A large U.S. study suggests that older adults who live very close to dry-cleaning businesses may have a higher risk of developing Parkinson’s disease.
The researchers found that the association was strongest for people living within about 500 feet, or 152 meters, of a dry cleaner.
The study was led by researchers at Barrow Neurological Institute in Phoenix and examined Medicare information from nearly 19 million older adults across the United States. The findings were published as an early manuscript in the journal npj Parkinson’s Disease, with a final edited version expected after further review.
Parkinson’s disease is a disorder of the nervous system that becomes more common with age. It develops when brain cells involved in controlling movement become damaged or die, leading to problems such as shaking, stiffness, slower movement and difficulty with balance.
Parkinson’s can also affect much more than movement. Some people develop sleep problems, depression, changes in thinking, constipation, loss of smell and other symptoms that can begin years before the disease is diagnosed.
Scientists do not believe Parkinson’s has a single cause. Age and genetics are important, but researchers increasingly suspect that environmental exposures may also contribute to the disease in some people.
The new study focused on dry cleaners because the industry has historically used powerful chemical solvents. These chemicals can remove grease and stains from clothing without washing the fabric in water.
Two solvents of particular concern are trichloroethylene, known as TCE, and perchloroethylene, or PCE. Both are chlorinated solvents that have been widely used in industry, and PCE has been especially common in traditional dry cleaning.
These chemicals do not always disappear when a business stops using them. If solvents leak or are improperly disposed of, they can enter soil and groundwater and remain in the environment for years.
Contamination can also spread beyond the original property. Chemicals in polluted soil or groundwater may release vapors that move through the ground, creating possible exposure routes for people living nearby.
To explore whether residential proximity might be connected with Parkinson’s, the researchers compared where older adults lived with the locations of dry-cleaning businesses. They then examined who later developed Parkinson’s disease.
People living within roughly 500 feet of a dry cleaner had a 14% higher risk of developing Parkinson’s than people living farther away. The association became weaker as residential distance from a dry cleaner increased.
This distance pattern is noteworthy because it is consistent with the possibility that a local environmental exposure could be involved. However, living near a dry cleaner does not prove that a person actually breathed, drank or otherwise came into contact with TCE, PCE or another solvent.
The researchers also looked at how Parkinson’s appeared in affected patients. The association was particularly strong among people who had walking and balance difficulties, falls and problems with thinking.
This raises the possibility that environmental factors could be related not only to whether Parkinson’s develops but also to the way the disease appears. Still, this part of the finding requires additional research before firm conclusions can be made.
The study also identified areas where the relationship appeared stronger. These included southeastern Illinois, parts of the Tennessee-Kentucky border region and Dallas, Texas.
Researchers do not yet know why these geographic differences appeared. Historical pollution, soil conditions, groundwater movement, local geology and older infrastructure could potentially influence how chemicals move through an area.
One major strength of the study is its enormous size. With records from nearly 19 million people, researchers were able to investigate a relatively uncommon disease across many communities and examine how risk changed with distance.
However, the study also has an important limitation: it measured proximity, not a person’s actual chemical exposure. A home near a dry cleaner may have little or no solvent contamination, while contamination from an old facility can sometimes extend beyond the closest homes.
Researchers also cannot know every place a person lived or worked throughout life from a simple residential comparison. Parkinson’s develops slowly, and an exposure many years or even decades before diagnosis could potentially matter.
The study is observational, so it cannot establish cause and effect. Other differences between neighborhoods or residents could partly explain the association even though researchers tried to account for known risk factors.
Senior author Dr. Brad Racette said the results add to growing evidence that environmental exposures may have an important role in Parkinson’s disease. Understanding preventable exposures could eventually offer new opportunities to reduce disease risk.
Overall, the study provides a strong reason to investigate solvent contamination around current and former dry-cleaning sites more closely.
The distance-related pattern and huge national sample make the findings important, but direct measurements of TCE, PCE and other pollutants will be needed to determine whether the chemicals themselves explain the increased Parkinson’s risk.
Source: Barrow Neurological Institute.
