Carlie Tanner, MD, PhD, professor of neurology at the Weill Institute for Neurosciences, University of California, San Francisco.
The Parkinson’s Plan, a new book detailing environmental and lifestyle factors in Parkinson’s disease (PD), is generating buzz among people and families living with PD. The Michael J. Fox Foundation (MJFF) spoke to Caroline Tanner, MD, PhD — a world-leading expert, neurologist and professor at the University of California, San Francisco — about her longtime study of Parkinson’s and the environment and what those with the condition (or individuals worried about their risk) should know and do.
MJFF: Is there evidence that shows environmental factors contribute to Parkinson’s? How might they interact with what we know about genetic forms of the disease?
Dr. Tanner: Some people do carry genetic mutations associated with PD, like those in the LRRK2 or GBA genes. But even if you have the mutation, you may never develop the disease. In fact, fewer than half of those with these genetic variants actually get Parkinson’s. Furthermore, the vast majority of cases — around 75 percent — don’t have a strong genetic cause.
So what tips the balance? That’s where environmental exposures come into play. It could be what you eat, what kind of work you do or where you live. We’ve seen clear associations between Parkinson’s and exposure to pesticides like rotenone and paraquat, as well as chlorinated solvents like trichloroethylene that were widely used in dry cleaning, degreasing and other manufacturing processes for decades. These toxic chemicals don’t break down and can contaminate water, soil and air. In fact, more than 17 million U.S. residents are estimated to be exposed to drinking water contaminated with TCE, and an even greater number may face exposure through the air.
What’s also interesting is that even if people don’t have a genetic mutation for PD, their genetic makeup might still influence how environmental exposures affect them. It’s this interaction between genes and environment that is key to understanding — and eventually preventing — Parkinson’s.
MJFF: Are there specific actions people can take to reduce their risk of Parkinson’s?
Dr. Tanner: There are some very obvious things, such as exercising and healthy eating. People who followed a Mediterranean-type diet, even if they had toxicant exposure, were found to be less likely to develop Parkinson's. Staying physically active also seems to be associated with a lower risk. These lifestyle behaviors may help counteract inflammation and other mechanisms in the body that are triggered by certain environmental exposures.
Another important thing people can do is try to limit exposure to toxic chemicals that are persistent in the environment. If you’re using pesticides around your home, wear protective equipment like masks and gloves — not cloth gloves, but chemical-resistant ones — and thoroughly wash or get rid of them afterwards. If you can avoid using pesticides altogether, even better. Being mindful of air quality — especially on high-pollution days — can also help. On those days, consider taking precautions to reduce your exposure to pollutants, such as wearing a mask or staying indoors.
Another key point is advocacy. We need stronger regulations to reduce harmful exposures. For example, paraquat is banned in almost every country in the world, except the United States. Actions like this can help all of society in the long run in terms of protection.
MJFF: Parkinson’s is on the rise, with one recent study estimating the number of cases could grow to more than 25 million by 2050. Are environmental exposures fueling that increase?
Dr. Tanner: One example comes from a small study of one city in the Netherlands, which has strict pesticide regulations. Over a couple of decades, Parkinson’s rates there stayed pretty constant. But in Olmsted County, Minnesota — a rural, more agricultural area of the U.S., where there is less regulation — rates have gone up. While these anecdotes are not definitive proof, this does suggest that environmental exposures are contributing factors to an increase in Parkinson’s.
MJFF: Do you believe Parkinson’s is preventable if we tackle environmental causes?
Dr. Tanner: Cleaning up the environment can be our first line of prevention. I think Parkinson’s is preventable — at least in part — if we address harmful environmental exposures. If we could go back to a pristine world, we’d likely see fewer people developing the disease. Certainly, trying to diminish exposure to toxic chemicals would make a difference. We are also learning how to spot early signs of Parkinson’s — thanks to new tools like biomarkers, which are measurable indicators of a disease or condition in the body. That opens the door to a second line of prevention, where we could potentially identify people in very early stages of the disease and intervene with lifestyle changes like better diet and exercise, or even targeted therapies. If we do both of these things, I believe we can actually get rid of Parkinson’s one day.
To learn more about Parkinson’s and environmental factors:
Listen to a webinar about everyday environmental exposures and their connections to Parkinson’s disease.
Research into chemicals and toxins associated with Parkinson’s can build greater understanding of disease risk. Check out a few examples of MJFF-funded studies on environmental risk factors here.
Discover how the Michael J. Fox Foundation helps advance government policies for the Parkinson’s community — including environmental health — and how you can take action.