Parkinson’s Disease: Sniff test could predict risk up to a decade earlier

Research has revealed that older adults who scored poorly on sniff tests were almost five times more likely to develop Parkinson’s disease in the next 10 years, when compared with individuals who had a better sense of smell and scored higher on the test.

However, when the results were separated by race, there was no statistically significant association between a weaker sense of smell and increased Parkinson’s risk in black adults.

It was also found that sense of smell influences Parkinson’s risk more in men than it does in women.

What is Parkinson’s Disease?

Parkinson’s disease is a disorder of the central nervous system, which causes issues with movement, balance, and coordination. It is estimated that more than 10 million people in the world have Parkinson’s.

Previous research has suggested that a reduction in sense of smell could possibly be an early indicator of Parkinson’s, appearing as long as years before the onset of symptoms. However, not all adults who experience a reduced sense of smell go on to develop the disease.

During the latest study, Dr Chen and colleagues set out to further investigate this association – particularly how far in advance olfactory loss may predict the risk of developing Parkinson’s disease, and whether the association varies between different races. 

Parkinson’s risk increased almost fivefold

The study included 2,462 adults aged 75 years on average. These people were also a part of the Health, Aging, and Body Composition study, an interdisciplinary study that focuses on risk factors for functional decline in older adults (2). Of these adults, 1,510 were white and 952 were black.

The participants completed a smell test that assessed their ability to correctly identify 12 different odours, including cinnamon, onion, soap, and gasoline.

The participants were then divided into three groups based on their scores – a poor sense of smell, a medium sense of smell, and a good sense of smell.

The participants were then followed for an average of 10 years, with the researchers noting any Parkinson’s disease development during that time.

A total of 42 subjects developed Parkinson’s in this time – 30 of whom were white and 12 were black.

Overall, it was concluded that participants who scored poorly on the smell test were almost five times more likely to develop Parkinson’s disease than the participants who were identified as having a good sense of smell.

The findings remained after accounting for possible contributing factors, including a history of head injury, smoking, and coffee intake.

Differences by sex and race

While the link between poor sense of smell and increased Parkinson’s risk was obvious during the entire follow-up period, the link was found to be strongest within the first 6 years after the test.

“Earlier studies had shown prediction of Parkinson’s disease about 4 to 5 years after the smell test was taken,” notes Dr Chen. “Our study shows that this test may be able to inform the risk much earlier than that.”

The researchers also discovered that men with a poor sense of smell were considerably more likely to develop Parkinson’s disease than women who had also been discerned to have a poor sense of smell.

It was also revealed that the link was not statistically significant for black adults.

“Reasons for this potential racial difference are unclear,” say the authors. “One possibility is that, compared to white participants, the etiology of olfactory dysfunction in black participants is more diverse and complex, and that Parkinson’s disease-related pathology is a relatively minor contributor.”

The team stressed that the findings should be interpreted with caution, and that further studies are required before a sniff test can be used to detect Parkinson’s, but they believe that their findings may pave the way (1).

(See also our articles Parkinson’s: Autoimmune Attack May Start Years Before Diagnosis and The Chemical Driving The Increase In Parkinson’s Disease)

References

1. Whiteman H. Parkinson’s: Sniff test could predict risk up to a decade earlier. Medical News Today. September 7, 2017.

2. Health, Aging, and Body Composition study. National Institute on Aging (NIH).