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Parkinson’s disease has been a rare disorder for most of human history. Yet a combination of aging demographics and byproducts of industrialization may have created a Parkinson’s pandemic, according to a 2018 review of studies in the Journal of Parkinson’s Disease.
In 2022, the World Health Organization (WHO) reported that disability and death due to Parkinson’s disease are increasing faster than for any other neurological disorder, including Alzheimer’s disease.
Parkinson’s Has Become a ‘Pandemic’
In 1817, Dr. James Parkinson first described the condition in London. It was rare, and he only found six individuals with the disease.
However, 200 years later, in 2015, over 6 million individuals lived with it, according to the 2018 review. Furthermore, findings indicate that the number of people with Parkinson’s disease is predicted to double from 6 million in 2015 to over 12 million by 2040, primarily due to aging.
According to the Global Burden of Disease study, neurological disorders are currently the leading source of disability worldwide. The fastest-growing of these in age-standardized rates of prevalence, disability, and deaths, is Parkinson’s disease.
The 2018 review of studies finds Parkinson’s, while noninfectious, exhibits traits that identify it as a “pandemic” disease.
In the United States, it was previously thought that there were about 60,000 diagnoses of Parkinson’s annually, but a new study in the journal NPJ Parkinson’s Disease revealed that the incidence is actually 50 percent higher than former estimates.
Besides steeply increasing prevalence and diagnosis rates, Parkinson’s has other similarities to a pandemic disease.
Like a pandemic illness, it extends over large geographic areas. Parkinson’s is increasing everywhere but appears to be shifting in response to population aging and industrialization changes.
In 2017, Parkinson’s cost the United States about $52 billion per year, and that figure was projected to increase to nearly $80 billion annually by 2037.
“By 2040, we can truly talk about a pandemic that will result in increased human suffering, as well as rocketing societal and medical costs,” Dr. Patrik Brundin, editor-in-chief of the Journal of Parkinson’s Disease, said in a statement.
While the reasons for the steep rise in Parkinson’s disease rates aren’t entirely clear, three main factors have contributed to this trend.
The No. 1 risk factor for Parkinson’s disease is age.
Longevity is a prerequisite for many diseases, including Parkinson’s disease. “Outside of rare genetic forms, the disease is rare at a very young age,” said Dr. Ray Dorsey, professor of neurology at the University of Rochester and author of “Ending Parkinson’s Disease.”
The percentage of Americans 65 and older nearly quadrupled (pdf) from 4.1 percent in 1900 to 16 percent in 2019.
Parkinson’s disease is believed to be caused by the loss of neurons that produce dopamine—a neurotransmitter that plays a critical role in controlling movement.
As we get older, our brains become less efficient at repairing damage and fighting off oxidative stress. Also, the number of dopamine-producing neurons in the brain decreases.
Both can lead to decreased dopamine levels that contribute to motor symptoms of Parkinson’s disease, such as tremors, rigidity, and slow movement.
However, aging and even genetics “don’t get you from six to 6 million,” said Dorsey. “Environmental factors must be to blame.”
Most of Parkinson’s disease is due to environmental factors tied to the Industrial Revolution, said Dorsey. Among these products and byproducts are air pollution, certain herbicides and pesticides, and even a chemical used in dry cleaning.
For example, Dorsey said exposure to a paraquat herbicide has been associated with a “150 percent increased risk” of Parkinson’s disease, likely due to its ability to generate reactive oxygen species and cause oxidative stress in the brain.
“Paraquat, created in the 1950s, is considered one of the most toxic weed killers ever created,” said Dorsey. “It kills the weeds that Roundup cannot, [and has] been used to commit homicide and suicide.” The EPA’s website says, “One sip can kill.”
“The pesticide’s own manufacturer has apparently known about its toxic effects related to Parkinson’s for over 50 years,” Dorsey continued, and more than 30 countries have banned it.
Yet the United States has not.
“Instead, the weed killer is sprayed almost all over the country,” said Dorsey. Its use in recent years has doubled.
The same holds for the widely used dry cleaning chemical trichloroethylene (TCE). It is associated with a 500 percent increased risk of Parkinson’s disease, reproduces features of the disease in laboratory animals, and damages the parts of cells that are impaired in Parkinson’s disease.
TCE is also used to extract oils from vegetables and remove grease from metal parts. It evaporates quickly and can contaminate the air, water, and soil in areas where it is produced or used.
In January, the EPA said TCE “poses an unreasonable risk to human health.”
“Yet it still remains on the market,” said Dorsey. “And global use is waxing, not waning. Thousands of sites around the country have been contaminated by the chemical, including the Marine base Camp Lejeune.
“Many of us live near a contaminated site and do not even know it,” he warned.
Exposure to pesticides can increase the risk of Parkinson’s by 70 percent. Pesticides such as rotenone and organophosphates can damage mitochondria, the energy-producing structures in cells, leading to oxidative stress and neuron death.
According to the NPJ Parkinson’s Disease study, these could partly explain why Parkinson’s incidence rates are higher in the Northeastern and Midwestern United States, called the “Rust Belt,” where industrial manufacturing has been common. However, this increase was also observed in Southern California, Southeastern Texas, Central Pennsylvania, and Florida.
“Understanding the source of these variations will be important for health care policy, research, and care planning,” Dr. Allison Willis, associate professor of neurology at the Perelman School of Medicine at the University of Pennsylvania, said in a statement.
Evidence suggests that infection with certain viruses can increase the risk of developing Parkinson’s disease. One such virus is the herpes simplex virus (HSV).
HSV is a common virus that causes cold sores and genital herpes. While most people infected with HSV experience mild or no symptoms, some individuals may develop more severe neurological complications.
Recent research suggests that HSV may also contribute to the development of Parkinson’s disease. HSV has been found in the brains of individuals with Parkinson’s disease, and research shows that exposure to the virus can induce inflammation and neuron death in the brain.
A systematic review of studies found there may be a link between COVID-19 infection and developing Parkinson’s, since the virus can cross the blood–brain barrier, and a mouse study finds the SARS-CoV-2 virus could increase the risk of brain degeneration seen in Parkinson’s disease.
Other viruses that have been linked to an increased risk of Parkinson’s disease include the influenza virus and the coxsackievirus.
Addressing the Crisis
The most effective therapy for Parkinson’s disease, levodopa, is decades old, and there is no known cure for Parkinson’s, but there are ways we might address the growing crisis.
“The solution to addressing Parkinson’s is prevention,” said Dorsey.
While the exact mechanisms by which viral infections contribute to the development of Parkinson’s disease are not fully understood, people can implement strategies to decrease their risk of contracting viruses associated with Parkinson’s.
For example, HSV can be prevented by avoiding certain sexual behaviors and avoiding oral contact with infected people.
Also, an increasingly older population should be encouraged to get regular physical activity, which has been shown to improve motor function and reduce the risk of developing Parkinson’s disease.
“[Those] who exercise and control diabetes and hypertension have a lower risk of being diagnosed with Parkinson’s disease,” said Dr. Bibhuti Mishra, chief of neurology at Long Island Jewish Forest Hills, part of Northwell Health in New York.
Importantly, reduce the intake of foods grown using pesticides and herbicides, and try to decrease exposure to toxins in daily life.
“If we ban paraquat, TCE, and the closely related dry cleaning chemical perchloroethylene (PCE), and clean up our air, we can all live in a world where Parkinson’s is increasingly rare, not common,” said Dorsey.
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