Where a person lives may offer clues about their future risk of Parkinson’s disease.
New research involving nearly 19 million older Americans found a small but measurable increase in Parkinson’s among people whose homes were very close to dry cleaners.
The study was conducted by scientists led by Barrow Neurological Institute in Phoenix. It was released in npj Parkinson’s Disease as an early, unedited manuscript so the findings could be made available before the journal completes its final editorial process.
The researchers found that adults living within about 152 meters, or 500 feet, of a dry cleaner had a 14% greater risk of developing Parkinson’s disease than those who lived farther away. The relationship weakened as the distance increased.
That does not mean living beside a dry cleaner gives someone a 14% chance of getting Parkinson’s. It means the relative risk was 14% higher in the closest group compared with the reference group in this study.
Parkinson’s is a progressive brain disease that affects movement and many other body functions. It is usually diagnosed later in life and can cause tremor, muscle stiffness, slow movement and difficulty walking.
As the disease advances, some patients also experience falls, balance problems and changes in memory or thinking. Researchers are still trying to understand why the brain cells affected by Parkinson’s become damaged.
Genes can increase susceptibility, but genetics alone cannot explain every case. Environmental chemicals have therefore become an important area of Parkinson’s research.
Dry cleaning attracted the researchers’ attention because of the solvents historically used to clean clothes. Traditional dry cleaning relies on chemicals that can dissolve oil and grease without soaking clothing in water.
Perchloroethylene, commonly shortened to PCE or perc, became one of the most widely used dry-cleaning solvents. Another chemical, trichloroethylene or TCE, was used for various industrial purposes and was also historically connected with cleaning operations.
Scientists have been studying whether long-term exposure to these chemicals may harm the nervous system. Previous research has raised concerns about a possible connection between chlorinated solvents and Parkinson’s disease.
Environmental contamination can last much longer than the business activity that created it. Solvents released into the ground may remain in soil or groundwater, and some can slowly move through underground areas.
PCE can also break down into other chemicals, including TCE, under certain environmental conditions. This means a site may remain relevant even if the original dry cleaner closed years ago.
In the new analysis, researchers used Medicare records to study nearly 19 million older adults. They examined whether the distance between a person’s residence and a dry-cleaning location was associated with a later Parkinson’s diagnosis.
The strongest relationship occurred among residents living closest to dry cleaners. As people lived farther away, the association with Parkinson’s gradually became smaller.
Scientists often pay attention to this type of distance pattern because it can support the idea of a nearby environmental source. If a pollutant is concentrated near its source, exposure might also decline as distance increases.
But distance is only a rough substitute for exposure. The researchers did not measure solvent levels inside each participant’s home, drinking water, soil or blood, so they cannot say whether the people who developed Parkinson’s were actually exposed to higher amounts of PCE or TCE.
Another interesting finding involved the symptoms of people who developed Parkinson’s. The association with dry-cleaner proximity appeared strongest in patients with walking and balance difficulties, falls and cognitive problems.
This may suggest that environmental exposure is connected with particular forms or features of the disease. Alternatively, other differences among these patients could explain the pattern, so it should be treated as a clue rather than a settled conclusion.
The study also found geographic hot spots where the relationship was stronger. They included southeastern Illinois, the area around the Tennessee-Kentucky border and Dallas, Texas.
Local environmental conditions might help explain these differences. For example, groundwater movement, soil type, historical disposal practices or aging pipes and infrastructure could affect how contamination spreads.
The nationwide size of the study is a major advantage. A database containing millions of older adults allows researchers to detect patterns that smaller studies may miss and to compare different parts of the country.
At the same time, the research cannot prove that dry-cleaning chemicals caused Parkinson’s disease. People living near dry cleaners may differ in other ways, and researchers cannot perfectly reconstruct every participant’s environmental exposure over many decades.
This long time period matters because Parkinson’s disease does not suddenly develop after a single recent event. Changes in the brain can begin years before diagnosis, making it difficult to determine which past exposures were most important.
The findings therefore should not be interpreted as evidence that everyone living near a dry cleaner is in danger. A 14% relative increase is a population-level association, and an individual person’s risk depends on age, genetics, health history and many other factors.
Overall, the study adds an important piece to the growing evidence connecting environmental chemicals with Parkinson’s disease.
Its strongest contribution is the clear relationship between distance and risk across a huge population, while its biggest weakness is the absence of direct measurements showing which chemicals people actually encountered.
Future studies that combine medical records with measurements of soil, groundwater, indoor air and historical contamination could provide much stronger answers. If solvents are eventually confirmed as preventable contributors to Parkinson’s, cleaning up contaminated sites and reducing exposure could become part of disease prevention.
Source: Barrow Neurological Institute.
