A federally funded study, headed by MSU researcher Honglei Chen, claims to have found a link between poor sense of smell and a higher risk of developing Parkinson’s disease.
The study, which tracked nearly 2,500 participants for an average of ten years, performed a smell test which rated each participant’s sense of smell as either poor, medium or good. Sixty-two percent of the participants who developed Parkinson’s over the course of the study had a “poor” sense of smell.
For the last 15 years, Chen has been researching the earliest signs and risk factors of the degenerative disorder. Since finishing post-doctoral work at Harvard, he has seen those in his field begin to understand Parkinson’s prodromal period, the time when initial symptoms may exist but are more difficult to detect.
“By looking at snapshots of risk factors in relation to disease outcomes, we’ve largely ignored the decades-long Parkinson’s prodromal development,” Chen said. “(Previous research) did generate a lot of information about Parkinson’s, but it really does not help us to understand just how complicated this process is.”
Because Parkinson’s affects a person’s motor skills, some obvious indicators of the disease include shaking and difficulty walking. However, Chen’s study intended to detect the less obvious signs of Parkinson’s: non-motor symptoms, which may help the disease be detected even earlier.
“I did a lot of research to look at risk factors for Parkinson’s, and gradually, the field evolves and we understand that Parkinson’s takes really a long time to develop,” Chen said.
The epidemiologist said that his study shouldn’t be misinterpreted. Failing a scratch-and-sniff test at an older age isn’t necessarily a sign of early-onset Parkinson’s. Poor sense of smell is also associated with Alzheimer’s and other neurological diseases, and many other, less serious reasons may exist for someone’s poor sense of smell. For Black participants in particular, no statistical significance was found in a link between one’s sense of smell and development of the disease.
“Sense of smell can be used to categorize populations at risk – it’s not ready for early identification,” Chen said. “At this stage, we gradually recognize this is an important symptom in prodromal PD, and can help us identify who might be at higher risk for the disease.”
Chen thinks his study has achieved what he hoped, but said that it should be seen as a stepping stone on the way to a larger goal, not the end of the line. He hopes future studies will similarly focus on the earliest warning signs of Parkinson’s, in the hopes of better clinical management and eventually prevention of the disease.
“This gives us a lot of hope that maybe, by studying these symptoms, we may be able to identify the disease early and to intervene early, which is really key for Parkinson’s disease,” Chen said.
He’s already following up on his previous research, and there’s clearly an audience for it. Chen is working on a study researching risk factors for sensory impairment such as air pollution, which recently received funding from the Department of Defense.
“In the next four years we will be really busy with this and hopefully some other projects surrounding sense of smell and prodromal Parkinson’s disease,” Chen said. “This now has become an important part of my research.”