Researchers at Michigan State University have found that a poor sense of smell during older age may be associated with an increased likelihood of dying within the next ten years. “Poor olfaction is associated with higher long-term mortality among older adults, particularly those with excellent to good health at baseline,” writes the team.
However, they can’t explain why.
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Epidemiologist Honglei Chen says the study is the first to explore potential reasons for why a poor sense of smell, which becomes more common as people age, is associated with an increased risk for death.
As reported in the journal Annals of Internal Medicine, the team used data from the National Institute on Aging's Health ABC study to analyze almost 2,300 people (aged between 71 and 82 years) over a 13-year period.
Each participant completed a test that assessed their ability to identify 12 common odors including lemon, cinnamon, and gasoline. The cohort was then divided into individuals who had a good, moderate or poor sense of smell and tracked for survival over the next 13 years.
Compared with individuals who had high smell test scores, individuals who correctly identified no more than eight odors were 46% more likely to have died at ten years and 30% more likely to have died at 13 years.
The authors say the results were slightly affected by factors such as lifestyle, gender and race. However, the interesting finding was that individuals who were healthier at baseline were found to account for most of the increased risk.
Further analysis revealed that poorer olfaction was not associated with death caused by respiratory conditions or cancer, but was significantly associated with death caused by Parkinson’s disease and dementia. There was also a modest association between increased mortality risk and cardiovascular disease.
‘We don’t have a reason’ for this
A poor sense of smell is known to be an early indicator of Parkinson’s disease and dementia. Scientists also believe that a poor sense of smell may decrease appetite, leading to weight loss and deteriorating health. However, these conditions only accounted for 28% of the deaths in this study, leaving most of the association unexplained.
“Neurodegenerative diseases and weight loss explain only part of the increased mortality,” writes the team.
"We don't have a reason for more than 70% of the increased risk. We need to find out what happened to these individuals," says Chen, who plans to investigate potential reasons in further studies.
Chen points out that a poor sense of smell may be an early and even sensitive predictor for deteriorating health, but that people are often unaware that their sense of smell is worsening and it is rarely factored in during health checks by doctors.
In the future, as these potential health implications are unveiled, it may not be a bad idea to include a sense of smell test as part of your [doctor’s] visit. Incorporating a sense of smell screening in routine doctor visits might be a good idea at some point."