A simple smell test may one day be able to help identify people at greater risk of developing Parkinson’s disease up to 10 years before the disease could be diagnosed, a new study claims.
Poor olfaction predicts Parkinson’s disease in short and intermediate terms, according to Chen et al. Image credit: Northwestern University.
Led by Honglei Chen of the Michigan State University College of Human Medicine, the study found that older adults with a poor sense of smell are more likely to develop Parkinson’s disease than people who perform better on the smell test. They also found that the link was stronger in men than in women.
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.’
The study involved 1,510 white people (mean age 75.6 years) and 952 black people (75.4 years) who took the test and were then followed for an average of 10 years.
Then researchers looked to see who had developed Parkinson’s disease during that time.
The participants were divided into three groups based on their scores on the smell test: poor sense of smell, medium and good.
During the study, 42 people developed Parkinson’s disease: 30 white people and 12 black people.
People in the poor sense of smell group were nearly 5 times more likely to develop the disease than people in the good sense of smell group.
Of the 764 people with a poor sense of smell, 26 people developed Parkinson’s disease, compared to seven of the 835 people with a good sense of smell and nine of the 863 people with a medium sense of smell.
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 study showed a strong association between the smell test and development of Parkinson’s up to 6 years later. The association remained beyond 6 years, but was not as strong.
“Earlier studies had shown prediction of Parkinson’s disease about 4-5 years after the smell test was taken. Our study shows that this test may be able to inform the risk much earlier than that,” Dr. Chen said.
“Not everyone with low scores on the smell test will develop Parkinson’s disease.”
“More research is needed before the smell test can be used to screen for Parkinson’s disease in the general population because the disease affects a low percentage of the population and because a low score on the test does not rule out other causes of problems with smelling.”
“One limitation of the study was that while the study participants were followed over time, determining which participants developed Parkinson’s disease occurred at the end of the study, so it’s possible that some cases may have been missed or mistakes made, especially since the disease can take a long time to diagnose in some cases.”
The study was one of the first to look at the sense of smell and Parkinson’s disease in black people.
“Previous studies have shown that black people are more likely to have a poor sense of smell than whites and yet may be less likely to develop Parkinson’s disease,” Dr. Chen said.
“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. More research is needed to further investigate a possible link.”
The team’s findings are published in the journal Neurology.
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Honglei Chen et al. Olfaction and incident Parkinson disease in US white and black older adults. Neurology, published online September 6, 2017; doi: 10.1212/WNL.0000000000004382
