Researchers in Arizona have found that living within 500 feet of a dry cleaner may increase the risk of developing Parkinson's disease by 14 percent. The study suggests that toxic chemicals remaining in the soil long after stores close could be driving an increase in diagnoses across the United States.
Parkinson's is a devastating neurodegenerative disorder in which parts of the brain become damaged over time. It causes progressively worsening tremors and movement problems that eventually rob patients of their independence.
The disease currently affects one million Americans and is thought to be on the rise in the US. Health experts have previously blamed the increase on environmental pollution, pesticides and smoking.
Researchers say that living near a dry cleaner may raise the risk of Parkinson's disease because of the chemicals used in the cleaning process. Dry cleaners use powerful chemicals to strip stains out of clothing.
Since the 1950s, many dry cleaners stopped using tetrachloroethylene, also known as TCE, due to its toxicity. Most businesses switched to a lighter chemical called perchloroethylene, or PCE, though PCE can degrade into TCE in the environment.
Scientists warn that these chemicals leach into the soil surrounding dry cleaning shops and can be released in vapor plumes that nearby residents breathe in. People may also bring home chemicals on treated clothing.
Chemical effects on the brain
Once inside the human body, scientists say the chemicals can pass into the brain and kill neurons that release dopamine, which helps control movement. The loss of these specific neurons triggers Parkinson's disease.
The researchers cautioned that their study, published this week in npj Parkinson's disease, does not prove that dry cleaning chemicals cause Parkinson's. However, they stated that the findings demonstrate a potential association that requires further investigation.
In the study, the scientists wrote: "Our findings suggest that chemicals used in dry cleaning may contaminate nearby neighborhoods and contribute to Parkinson's disease risk."
Data from the Parkinson's Foundation estimates that 1.2 million Americans will have the disease by 2030. Currently, 90,000 people are diagnosed with the condition every year in the United States.
That figure represents a 50 percent increase from the previous estimate of 60,000 new annual cases recorded a decade ago. Approximately 35,000 people die each year from Parkinson's disease, with deaths often caused by swallowing difficulties and pneumonia.
Only about 15 percent of Parkinson's cases are diagnosed in patients with a family history of the disease. Last month, singer Carly Simon announced that she was diagnosed with Parkinson's disease, though there is no suggestion her condition is linked to dry cleaning.
Analysis of Medicare patient records
To conduct the research, scientists analyzed the medical records of Medicare patients aged 67 and older nationwide. Over a five-year period ending in 2018, the team checked each patient record for a Parkinson's diagnosis.
The study evaluated a total of 18 million people and identified 180,000 cases of Parkinson's disease across the country. Researchers extracted patient location data and compared it to the locations of nearly 33,000 dry cleaning businesses operating in 2013.
After adjusting for other risk factors, the analysis revealed that living within 0.1 miles, or about 2,000 steps, of a dry cleaner was linked to higher risks for specific subtypes of the disease compared to living four or five miles away.
Living within 0.1 miles increased the risk of Parkinson's disease with gait instability by 23 percent. Gait instability is one of the two most common subtypes of Parkinson's, characterized primarily by problems with walking or balance.
Living within 0.1 miles was also linked to a 25 percent higher risk of being diagnosed with Parkinson's disease alongside dementia or cognitive decline. Additionally, it carried a 19 percent higher risk of diagnosis following a fall.
The researchers found no significant association between living near dry cleaners and tremor-defined Parkinson's, which is the other main subtype where tremors are the primary symptom.
Geographic clusters and study limitations
Nationwide, researchers identified the strongest link between dry cleaners and Parkinson's in the New York City metropolitan area, southern California, Michigan and parts of the South.
Stronger associations were also observed in the Dallas-Fort Worth and Detroit metropolitan areas, southern Illinois, the Tennessee-Kentucky border, central Pennsylvania and north-central Indiana.
The study noted several research limitations, including that the accuracy of patient location data could not be verified independently. The analysis also assumed that patients had lived in the same location near dry cleaners over time.
Furthermore, some dry cleaning storefronts only serve as drop-off and pick-up locations, with actual cleaning performed at a separate offsite facility. Other neighborhood risk factors, such as general environmental pollution, could not be discounted.
Dry cleaning chemicals can linger in the soil around a business site for decades after a shop closes down. In light of chemical risks, scientists have previously advised people to take steps to reduce exposure to toxic substances.
Recommended preventative actions include washing all fresh produce to remove pesticides, choosing dry cleaners that do not use PCE or TCE, and avoiding golf courses shortly after pesticide treatments.
