American Scientist:
The Rise of Parkinson's Disease
Published 2020
By E. Ray Dorsey, Todd Sherer, Michael S. Okun, Bastiaan R. Bloem
"Neither our increased awareness of the disease nor our lengthening life spans can fully account for the upsurge in diagnoses that we now face. Our knowledge of another neurological disorder, multiple sclerosis, has increased too, and we have improved diagnostic tools for it. Rates for multiple sclerosis have indeed gone up, but that increase is nothing like the exponential rise of Parkinson’s (see figure below). As for aging, more people are, of course, living longer. For example, from 1900 to 2014, the number of individuals over age 65 in the United Kingdom increased about sixfold. However, over that same period, the number of deaths due to Parkinson’s disease increased almost three times faster."
The increase in the number of Parkinson’s disease cases in England cannot be explained by an aging population or better diagnosis alone. Multiple sclerosis, another neurological disease, also has comparably improved diagnostics, but has not seen the exponential rise observed in Parkinson’s deaths. Changes in coding in the 1980s likely contributed to the fluctuations in deaths recorded during this period. As for age, the rate of increase in Parkinson’s far outpaces the increase in the elderly population in the United Kingdom.
Figure adapted from R. Dorsey et al., 2020.
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"While industrialization has increased incomes and life expectancies around the world, its products and by-products are also likely increasing the rates of Parkinson’s. Air pollution began to worsen in England in the 1700s, metal production and its harmful fumes increased in the 1800s, the use of industrial chemicals rose in the 1920s, and synthetic pesticides—many of which are nerve toxins—were introduced in the 1940s. All are linked to Parkinson’s—people with the most exposure have higher rates of the disease than the general population.
The evidence for this connection is overwhelming. Countries that have experienced the least industrialization have the lowest rates of the disease, whereas those that are undergoing the most rapid transformation, such as China, have the highest rates of increase. Specific metals, pesticides, and other chemicals have all been tied to Parkinson’s in numerous human studies. When animals are exposed to many of these substances in lab experiments, they develop the typical characteristics of the disease.
Agricultural areas have the highest rates of Parkinson’s. In Nebraska, the rates of the disease are two to four times higher in the state’s rural, agricultural parts than in urban Omaha, according to a 2004 study in
Movement Disorders. In Canada, investigators have found an almost perfect correlation between areas with the highest pesticide use and the highest rates of disease, as documented in a 1987 study in the
Canadian Journal of Neurological Sciences. In France, rural areas have the highest rates of Parkinson’s, as do the regions with the most vineyards, which often require intense pesticide use, according to a 2017 study in the
European Journal of Epidemiology.
Farmers who are exposed to certain pesticides have a higher risk of developing the disease. In one 1998 study published in
Neurology, the risk of developing the disease for farmers was 170 percent greater than that for nonfarmers. And the longer farmers have worked with pesticides, the greater their risk."
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"The U.S. Environmental Protection Agency (EPA) had at one time proposed banning one of the chemicals that is tied to Parkinson’s, a solvent called
trichloroethylene. But after lobbying by the chemical industry, the EPA decided in 2017 to postpone the ban indefinitely. The uses of trichloroethylene have been so numerous and widespread—in washing away grease, cleaning silicon wafers, removing spots in dry cleaning, and even, until the 1970s, decaffeinating coffee—that almost all of us have been exposed to it at some point in our lives. Some of these uses continue today. Almost half of Superfund sites—land so polluted that the EPA or the responsible parties have to clean it up—are contaminated with trichloroethylene. Thousands of other sites are polluted across the country.
As a result, as reported by the EPA, up to 30 percent of the U.S. drinking water supply has been contaminated with trichloroethylene. Because it readily evaporates from groundwater and soil, the solvent, like radon, can enter homes or offices through the air, undetected. Parkinson’s is not even the most concerning safety risk. According to the EPA, trichloroethylene also causes cancer.
But trichloroethylene is only one dangerous chemical that we have failed to protect ourselves against.
Paraquat is a pesticide so toxic that 32 countries, including China, have banned it. Exposure to the chemical increases the risk of Parkinson’s by 150 percent, according to a 2011 study in
Environmental Health Perspectives. Yet the EPA has done little. And as the agency charged with protecting our environment sits, paraquat’s use on U.S. agricultural fields has doubled over the past decade, according to data from the U.S. Geological Survey’s Pesticide National Synthesis Project.
The nerve toxin
chlorpyrifos is the most widely used insecticide in the country, drenching golf courses and dozens of crops, including almonds, cotton, grapes, oranges, and apples. It has been linked not only to Parkinson’s but also to problems with brain development in children. Again, the EPA has shelved a ban. When a federal court stepped in to take action against the chemical, the Trump administration appealed. And in July 2019, in response to a court ordering a final ruling, the EPA decided that it would allow continued use of chlorpyrifos."
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"Even though it was banned half a century ago, DDT persists in the environment—and in our food supply. It becomes more concentrated as it makes its way up the chain to human consumption. The pesticide is then stored in our fatty tissues.
In 2003 and 2004, more than 30 years after the insecticide was banned, the U.S. Centers for Disease Control and Prevention (CDC) tested the blood of about 2,000 people ages 12 and older. The researchers were looking for DDT and its metabolite, or breakdown product,
dichlorodiphenyldichloroethylene (DDE). They found in their 2009 report that “a small proportion of the population had measurable DDT [and] most of the [U.S.] population had detectable DDE” in their blood. For Parkinson’s, what matters more are the concentrations of chemicals in the brain, which may be several times those in blood, according to the Extension Toxicology Network, because DDT dissolves in fat."
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"Vietnam veterans and up to 4 million Vietnamese came into contact with Agent Orange during the Vietnam War.
There has been no large-scale study of the effect of this exposure on the health of the Vietnamese or war veterans. Smaller studies, however, have linked Agent Orange to many problems in these populations, including birth defects, cancer, and Parkinson’s, as summarized in a 2007 paper in
Science by Richard Stone of the Veterans Health Administration. The evidence is sufficient that veterans who were exposed to Agent Orange and now have Parkinson’s are eligible for disability compensation and health care from the U.S. Department of Veterans Affairs."
