Is Most Parkinson's Disease Man-Made and Therefore Preventable?

Indu Subramanian, MD; E. Ray Dorsey, MD


November 20, 2023

This transcript has been edited for clarity.

Indu Subramanian, MD: My name is Indu Subramanian, and I'm at UCLA in Los Angeles. It's my pleasure to have Ray Dorsey on our program today. Ray is a professor of neurology at the University of Rochester and has been doing some amazing advocacy work in largely the space of trying to end Parkinson's disease.

E. Ray Dorsey, MD: Thanks very much for having me, Indu. I'm delighted to be with you.

Trichloroethylene and PD

Subramanian: I wanted to first highlight some of the work that has come out and gotten a large amount of media attention around Camp Lejeune and specifically trichloroethylene (TCE) as a cause of Parkinson's, and one of the environmental toxins that we talk about as something that is in pretty much everywhere. This paper came out, and you wrote a commentary in JAMA Neurology as well. Perhaps we can summarize the paper and its findings.

Dorsey: Like most people, I didn't know what TCE was until about 5 or 6 years ago. TCE is a very simple molecule. It's got six atoms, including two carbon atoms, one hydrogen atom, and three chlorine atoms — hence, its name "trichloroethylene." There's a very similar chemical called perchloroethylene, which is widely used in dry cleaning. It's got one additional chlorine atom, and the prefix "per-" means "four." I'll talk about TCE predominantly, but both of these chemicals probably have similar toxicity with respect to Parkinson's disease.

Research done by Drs Carlie Tanner and Sam Goldman about a decade ago showed that in twins who were exposed to this through their work (it's widely used as a degreasing agent) or hobbies (it's used in printing and painting, by varnish workers, or by anyone that needs it as a solvent) had a 500% increased risk of developing Parkinson's disease. Importantly, in that study, they showed that there was a lag time of 10-40 years between exposure to that chemical and the diagnosis of the disease. Because TCE was so widely used, they said that public health implications could be substantial.

What's Camp Lejeune? Camp Lejeune is a Marine base in North Carolina where many Marines are trained. Between 1953 and 1987 at that Marine base, the drinking water was contaminated with TCE, perchloroethylene, and other toxic chemicals. The reason Camp Lejeune is so infamous is because the Marines knew about the contamination for many years and covered it up.

Indeed, this story only came to the forefront because Jennie Ensminger, the daughter of a Marine drill instructor, developed leukemia at age 6 and died at age 9. Her father, Jerry Ensminger, a retired master sergeant, found out after the fact that these cancer-causing chemicals, including TCE, a known carcinogen, were found at the Marine base and could be an explanation for why his daughter developed and died of leukemia.

Drs Sam Goldman and Carlie Tanner and colleagues from UCSF looked at the rates of Parkinson's among Marines who served at Camp Lejeune during the 1970s and compared that with rates in Marines who served Camp Pendleton on the West Coast. It turned out that the Marines who served at Camp Lejeune had a 70% higher risk of developing Parkinson's disease than the Marines who served at Camp Pendleton.

Importantly, these Marines, by definition, were healthy. They were young. They were only 20 years old, on average, when they were at Camp Lejeune. They only stayed at a Marine base for a short period of time, so on average, they were only there for 2 years. Yet 30 years later, they had a 70% increased risk of developing Parkinson's disease.

Ending Parkinson's Disease

Subramanian: Wow, that's pretty profound. You've done a large amount of work, and in fact you, along with some of our colleagues wrote a book about ending Parkinson's disease. I read that book when it came out a couple of years ago, and I was really struck by a few things. Parkinson's has doubled in the past 40 years and is going to double again in the next 20 years. Can you tell me a little bit about that statistic and why that is? It's not just because people are aging. What is the sense of that? How do we interpret that?

Dorsey: According to the Global Burden of Disease study, which I was fortunate to be part of, the number of people with Parkinson's disease has more than doubled in the past 25 years. A conservative projection based on aging alone suggests that it's going to double again unless we change something about it. It's now the world's fastest-growing brain disease, and it is growing faster than can be explained by aging alone.

If you look at the map of Parkinson's disease, if you thought it was purely genetic, you would have a relatively uniform map of rates of Parkinson's disease. In fact, we don't see that. Rates of Parkinson's are five times higher in industrialized parts of the world, like the United States and Canada, than they are in sub-Saharan Africa. Rates of Parkinson's disease are increasing most rapidly in areas of world that are undergoing the most rapid industrialization, such as India and China, where adjusted for age, the rates of Parkinson's have more than doubled in the past 25 years.

The thesis of our book is that much of Parkinson's disease is man-made. Work done by your colleagues at UCLA, including Jeff Bronstein and Beate Ritz, have demonstrated that air pollution and certain pesticides are likely fueling the rise of Parkinson's disease.

Given that in the United States, rates of Parkinson's disease are actually higher in urban and suburban areas than they are in rural areas, I think that this dry-cleaning chemical — which was widely used in the 1970s in everything from typewriter correction fluid to decaffeinated coffee and [over] 2 pounds per American [was produced] — could be one of the most important causes or contributing factors to Parkinson's disease.

What to Tell Patients

Subramanian: For the general neurologists or practitioners out there watching this, what can they do? If you have a patient whom you suspect may have been exposed to toxins, what should we tell people who aren't patients yet who are at risk? What are some things that you think would be helpful?

Dorsey: I think one of the shortcomings of American medicine is that we often just go from diagnosis to treatment. You're depressed, you get an antidepressant; you have Parkinson's disease, you get levodopa; you have seizures, you get put on an antiepileptic medication.

I think we need to spend a couple of minutes at least, maybe at the beginning, to go to the diagnosis of the condition and why you have this disease. If you just do a brief occupational history, after you start the exam — things like finding out what people do for a living or did for a living or how they spend their time — I think you'll find many of these risk factors are actually present.

It's pretty easy to identify whether people grew up in a rural area and drank well water, which is prone to be contaminated with pesticides. We know that people who drink [contaminated] well water have about a 75% increased risk of developing Parkinson's disease. I think you can find for people, especially when they grew up, when they were young, that the most relevant exposure might be that when people were young children.

It's a little bit harder to identify all exposure to TCE. The Marines at Camp Lejeune didn't know they were drinking the water that was contaminated with this and only found out about it after the fact because Jerry Ensminger launched a 26-year campaign to bring justice for the Marines and their dependents.

Some people who know that they work with chemicals or with solvents might know about this. In New York City, these chemicals are widely used in dry cleaning. They're readily volatile. These chemicals can evaporate from dry-cleaning buildings and go into the indoor air of apartments above dry cleaners, for example, in New York City. That can be in toxic levels. These readily dissolve in fat, hence their use in degreasing.

There have been studies, for example, in Germany, that found that supermarkets that are simply near a dry cleaner will have TCE or perchloroethylene in the butter and the cheese that they're selling.

It gets even worse. For example, you bring your daughter into the dry-cleaning building and she's eating an ice cream cone. When she leaves, she's eating perchloroethylene and TCE.

It's a little bit harder to find it, but I think it's relevant because some people might be still being exposed and some people might still be drinking well water and they rarely have their well tested. For those people, I recommend they get their well tested and I recommend all my patients to get a carbon filter to decrease exposure to pesticides and chemicals. A carbon filter is just like what Brita and Pure and other brands are.

Because they're chemicals known to cause cancer, I get a little bit concerned about cancer screening. This is most strongly tied to non-Hodgkin lymphoma, liver cancer, and renal cancer. It's also linked to multiple myeloma, prostate cancer, probably brain cancer, and probably breast cancer, especially in men.

I tell people to be concerned about those, and then I tell people to avoid pesticides if they have Parkinson's disease in all its forms, not only in the drinking water but in the produce you buy, the food you eat, what you put on your lawn, what's on the golf course where you play, and the like.

Subramanian: I would say, just from the wellness perspective, if people are at risk for degenerative disease in terms of their brain health, things like sleep, mind-body practices, exercise, diet (Mediterranean or organic, if you can), and avoiding pesticides are all important. Social connection is important as well — the things that we think are helpful in general as people age and to prevent Alzheimer's and other things like that.

Dorsey: These are fantastic ways to modify disease course. The evidence for them is only increasing. There's an analogy I like to use. If someone is diagnosed with lung cancer, the first thing we tell them to do is to stop smoking. If someone's diagnosed with Parkinson's, we don't tell them to stop getting exposure to pesticides. We don't tell them to stop dry cleaning their clothes. We don't tell them to avoid air pollution. These are all risk factors that are increasingly well established for Parkinson's disease.

I think Parkinson's disease, fundamentally for the vast majority of people, is an entirely preventable disease. We're not taking actions to prevent people from getting this very disabling and very deadly disease.

Advocacy Work

Subramanian: You and I are quite interested in the sense of being advocates as neurologists, and I think it fuels our passion and helps us to wake up every morning feeling like we have something that is meaningful and purposeful in our lives. Could you describe this as your passion and how it may prevent burnout and what it's given you as a neurologist?

Dorsey: The credit for much of this is Dr Carlie Tanner at UC San Francisco. I had the gift of sabbatical and I started reading the literature, I started reading her literature, and I came away with that, over the past 25 years, she detailed these environmental risk factors that are linked to Parkinson's disease. Pesticides, these dry-cleaning chemicals, and air pollution. When I read it, I just realized that this was the case.

The same time I was reading her work, I read this book called How to Survive a Plague by David France, who was a member of a group called Act Up, which was a group of men in New York City who reacted to the emergence of HIV in the 1980s. If you remember the 1980s, there was no federal response to HIV. People were blamed for the diseases that they were developing. It was only because brave men and women in New York City and in San Francisco banded together and organized that they changed the course of HIV.

They didn't just do it for themselves. They did it for all of us. You and I and many people listening may not have HIV because of their courage. They made HIV a treatable condition. It's actually more treatable than Parkinson's disease. It's associated with a near-normal life expectancy. They also made it a preventable disease. Thousands, if not millions, of us don't have HIV because of their work. It's an increasingly less common disease. Rates of HIV are actually decreasing, which is something that you or I would never have expected when we were in medical training.

I can't think of a better outcome for a neurologist or any physician to make the diseases that they're carrying for nonexistent and we lived in a world that didn't have HIV. We lived in a world where lung cancer largely didn't exist. We've had worlds in the past where Parkinson's probably didn't exist or existed in extremely small numbers. That might be true for diffuse Lewy body disease and others, and if these diseases are preventable, we can take actions as individuals and as a society to lower our risk.

What a wonderful gift for future generations and many generations to come, hopefully, to live in a world that's largely devoid of Parkinson's disease. Just like we live in a world free of typhus. We live in a world free of smallpox. We live in a world where polio is extraordinarily uncommon. We don't even have treatments for polio because we just don't have polio. I think we can do the same thing for Parkinson's disease for the vast majority.

Subramanian: Thank you so much, Ray, for your advocacy. We're getting to the point in neurology, which is exciting to me, of possibly primary prevention of some of these disorders. I think we have a role in that, which is exciting for the future.

Dorsey: Absolutely.

Follow Indu Subramanian on Twitter  @DrISubramanian

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