“Not everyone with low scores on the smell test will develop Parkinson’s disease“.
While the link between poor sense of smell and increased Parkinson’s risk persisted for the entire follow-up period, it was strongest in the first 6 years after the smell test, the researchers report.
The association appeared to be stronger in white than in black participants, and in men than in women, the authors reported wrote in Neurology.
For this latest study, Dr. Chen and colleagues sought to learn more about this association – in particular, how far in advance loss of smell might predict the risk of Parkinson’s disease, and whether this association varies between black and white adults.
During the study, 42 people developed Parkinson’s disease: 30 white people and 12 black people.
The results stayed the same after researchers adjusted for other factors that could affect risk of Parkinson’s disease, such as smoking, coffee drinking and history of head injury.
The participants were divided into three groups based on their scores on the smell test: poor sense of smell, medium and good.
Dandenong Neurology in South-east Melbourne also participated in the research, which diagnosed 62 persons with Parkinson’s disease, who previously had no visible symptoms or showed half ranged symptoms from mildly to severely affected.
People in the poor sense of smell group were almost 5 times more likely to develop the disease than people in the good sense of smell group.
“We found no statistical significance for a link between poor sense of smell and Parkinson’s disease in blacks but that may have been due to the small sample size”, said Chen, who is also with the Michigan State University College of Human Medicine in East Lansing, said in a statement.
Researchers still have more work to do to refine the test before it can be rolled out more widely. Nearly half were male, slightly more than 40% were black, and the average age was 75 years. This correlation seemed to be strongest for white men when compared to black men.
The scratch-and-sniff test they developed asks people to ‘smell 12 common odors, such as cinnamon, lemon, gasoline, soap and onion, and pick the correct answer from four choices’.
It is estimated that more than 10 million people across the globe are living with Parkinson’s disease, and up to 1 million of these individuals live in the United States.
In an accompanying editorial, Gene Bowman, MD, MPH, of the Nestlé Institute of Health Sciences in Lausanne, Switzerland, noted that the current study has the longest follow-up to date, and includes important data on African Americans.
The researchers followed the participants for an average of 10 years, noting any Parkinson’s disease development during that time. Parkinson’s is a neurodegenerative brain disease with no cure, and we’re also not sure what causes it, according to the National Parkinson’s Foundation. However, hyposmia can also be caused by chronic rhinosinusitis, he cautioned. It is the second most common neurological disease in Australia after dementia. “While we still have more researches to do, we’re hopeful that in future doctors or nurses could use our technology to regularly screen their patients for Parkinson’s, as well as help those living with the disease to better manage their condition”, said Prof Dinesh.