Experts estimate that the number of people with Parkinson's disease in the world could double over the next two decades.
In a report warning of a possible "Parkinson 's pandemic", researchers say the conditions are right for the number of cases to reach 12 million or more by 2040.
What is the blame? Trends are generally positive overall: older age is a major risk factor for Parkinson's disease and, as life expectancy increases worldwide, more people will develop the disease. At the same time, patients with Parkinson's disease survive longer, which increases the number of people with Parkinson's disease at some point.
There is also a less expected factor: the decline in the smoking rate. Although the habit has many devastating effects, research suggests that it protects against Parkinson's disease.
These are obviously trends that nobody wants to reverse, said Dr. Ray Dorsey, author of the report.
There are however other ways to slow the predicted progression of Parkinson's disease, said Dorsey, a professor of neurology at the Medical Center at the University of Rochester in New York.
"We think we can do a lot in prevention," he said.
At the top of the list are the reduction in people's exposure to certain pesticides, solvents and other chemicals that research has linked to Parkinson's risk.
For example, Dorsey mentioned weed killer paraquat. "This has been strongly linked to an increased risk of Parkinson's, and is banned in 32 countries," he said.
It is still used in the United States, however. And, noted Dorsey, some countries that have banned it – like England – continue to manufacture it and export it to other countries, including the United States.
Then there is trichlorethylene (TCE) – an industrial solvent that is a known carcinogen in humans and can contaminate groundwater, according to the US Department of Health.
TCE is also toxic to nerve cells, and studies have linked to Parkinson's disease, Dorsey said.
Parkinson's disease currently affects nearly a million people in the United States alone, according to the non-profit Parkinson Foundation.
The cause is uncertain, but as the disease progresses, the brain loses the cells that produce dopamine – a chemical that regulates movement. As a result, people suffer from symptoms such as tremors, stiff limbs, problems with balance and coordination. All get progressively worse over time.
Medications and other treatments can lessen these effects, but there is no cure.
The new report – co-authored by representatives of the Parkinson Foundation and the Michael J. Fox Foundation – paints a potentially bleak picture.
Between 1990 and 2015, the number of people diagnosed with Parkinson's disease worldwide doubled to just over 6 million. And on the basis of the aging population, Dorsey and his colleagues predict that this number will double again by 2040, reaching about 12 million.
But this figure, they say, could actually be higher – up to 17 million – with lower smoking rates and increasing industrialization taken into account.
"The world urgently needs to wake up and recognize that a new wave of Parkinson's is getting ready," said Dr. Michael Okun, Parkinson Foundation's Medical Director and author of the report.
In addition to the broader ban on paraquat and TCE, Mr. Dorsey said other measures could help stem the tide.
For example, people with a history of head trauma have a relatively higher risk of Parkinson's. So preventing head injuries in the workplace, in sports or at leisure – wearing a helmet for example – could help, Dorsey said.
There is also evidence that some healthy lifestyle habits are protective – namely vigorous physical exercise and the Mediterranean diet.
But beyond prevention, health care systems need to prepare for a resurgence of Parkinson's, according to Okun.
"The number of patients with Parkinson's disease is growing at a rate that will overwhelm global health systems," he said.
According to Dorsey, a key step will be finding ways to bring health care to patients at home.
"If I am an elderly person with Parkinson's who can no longer drive," he said, "I need care to come to me."
Of course, many patients will have family members who can help you. But this raises another major problem: the burden of caregivers.
Already in the United States, more than 30 million people are caring for an adult aged 50 or older, Dorsey said.
"The main reason," he said, "is neurological conditions, like Alzheimer's and Parkinson's."
The report was published recently in a supplement to the Journal of Parkinson's Disease.