The evidence is overwhelming, environmental factors play a role in almost all chronic and degenerative diseases. According to the WHO, 23% of all deaths are linked to the environment. Yet, few people are seriously studying the specific factors responsible or how we might be able to address them.
But, there are some that do.
This is Prof. Honglei Chen. He is an environmental epidemiologist at Michigan State University College of Human Medicine where he studies how the environment impacts brain health with a focus on Parkinson’s disease.
“I think we all agree that environmental factors play a part, but they are incredibly difficult to study. The environment includes many different factors that may change over time, it is far more than just pesticides or toxins.”
This includes such factors as nutrition, lifestyle, host-environment interactions, gut microbial populations, and much more. Each is critical to keeping us alive and healthy.
“Also when it comes to Parkinson’s disease, we know now that this is not just a disease of the brain. The disease involves multiple systems, for example, the gut and the olfactory pathway may be where the disease gets started.”
Yet, getting any traction on this issue has been a frustrating campaign for many, even substances that have long been known to be responsible for elevating one’s risk for Parkinson’s disease have been difficult to remove from the market. One such example is the herbicide paraquat, already banned by 32 countries, now the Michael J. Fox Foundation is trying to do the same in the US, though many previous attempts to do so have been stifled.
One particular area that is drawing attention is gene-environment interactions. There is a long list of genetic mutations that elevate risk for diseases like Parkinson’s disease. However, almost all of them have incomplete penetrance, meaning that most people who have them will not go on to get the disease. One likely explanation is that only in combination with exposure to the right set of environmental factors will those genetic variants trigger disease.
The problem is that very few people are studying both sides of this equation. There are hundreds of labs studying the genetic risk factors, but only a few trying to account for environmental factors.
“We need to embrace the uncertainty involved with studying the environment and how it impacts health.” Says Prof. Chen, “In the past two decades we have seen a lot of progress in understanding the genetic risk factors for PD, this is because we can read our genome and get accurate genetic data at a fairly low cost.”
To further complicate matters, those who do study environmental exposure in PD do so in the context of the likelihood of getting disease, but ever fewer study factors that affect the rate of disease progression, which is what patients care most about.
“I agree that it is really important to study the disease risk factors, but we should also understand that Parkinson’s is a continuous process rather than an isolated diagnosis. From disease initiation to the end, we are talking about decades.”
“Many factors can come into play, either cumulatively or at certain points. We need a lot of studies from various perspectives to figure out the factors that affect progression over the course of the disease. There are quite a few studies about physical activities and its benefits to quality of life. We should also study factors such as nutrition as we know it plays an important role but we don’t know enough about the specific details involved.”
Another focus of Prof. Chen’s work is in studying what are called the prodromal symptoms of Parkinson’s disease, this refers to the earliest signs of disease. These symptoms can manifest years, or in some cases, decades before the typical symptoms associated with Parkinson’s present themselves. Some believe that exposure to environmental risk factors could be the trigger that sets this process in motion.
“Some of the symptoms that come to the top are hyposmia (loss of sense of smell), REM sleep behavior disorder (RBD), and constipation. I think these three symptoms need a lot of attention. For example, the vast majority of late-onset Parkinson’s patients start to have loss of smell about a decade before onset. It is associated with a five-fold increase in the chance of getting Parkinson’s disease.”
“But 15-25% of elderly people have a poor sense of smell, (while) the lifetime risk of Parkinson’s disease is about 2%. If you put them together, among those with a poor sense of smell, the risk is higher, but not really that much higher, it could be 6-15%, which is still not enough to warn somebody with a poor sense of smell that they might get Parkinson’s. But smell itself is a very complicated area and we need to be able to better characterize it so we can better predict whether someone with hyposmia will go on to develop Parkinson’s disease.”
Neurodegenerative diseases are increasing dramatically all around the world. A recently released study from the Bill and Melinda Gates Foundation found that between the years 1990 to 2016 the world went from 2.5 million cases of Parkinson’s disease to 6.1 million, making it the fastest growing neurodegenerative condition. Without a renewed focus on studying the environmental factors, we might never get ahead of these diseases.
(Click here for more analysis on this study from the Science of Parkinsons)
(For more you can listen to the full audio of my conversation with Prof. Honglei Chen below)