Older adults who have a poor sense of smell may be at increased risk of dying within 10 years, particularly from neurodegenerative disorders such as dementia and Parkinson’s disease, according to a study published this week in the journal Annals of Internal Medicine.
The study also found the risk was greatest among people who initially reported themselves in good or excellent health.
This isn’t the first study to link a poor sense of smell to an increased risk of death in older adults. Previous studies, however, have tended to follow people for only a short time (five years or less) and didn’t always control for people’s existing health conditions.
The current study is an attempt to overcome the limitations of those earlier studies — and to get a better understanding of the specific types of deaths for which a loss of smell may be a predictor.
“Poor sense of smell becomes more common as people age, and there’s a link to a higher risk for death,” said Dr. Honglei Chen, the study’s senior author and an epidemiologist at Michigan State University, in a released statement. “Our study is the first to look at the potential reasons why it predicts a higher mortality.”
How the study was done
For their study, Chen and his colleagues used data collected from 2,289 participants in the federally funded Health, Aging and Body Composition (ABC) Study, which has been collecting health information since 1997 on a group of black and white adults living in Memphis and Pittsburgh. The participants were aged 71 to 82 and generally healthy at the start of the study. At that time, all completed a standardized “smell test” of 12 common odors, such as onion, soap, gasoline, lemon, chocolate and rose.
The participants were presented with four options for each odor, and were given a point for each correct answer. Using that point system, the participants were then categorized as having a “good,” “moderate” or “poor” sense of smell.
Chen and his colleagues followed the participants for 13 years. At the end of that period, 1,211 of them had died. The researchers then looked to see if there was any association between the participants’ scores on the smell test and their risk of death at various points over the 13 years.
No association was found at the three- or five-year mark of the study. But ones were found at later time-points. Compared with the older adults with a good sense of smell, those with a poor sense of smell had a 46 percent higher risk of dying by 10 years and a 30 percent higher risk by 13 years. (The researchers believe the risk was lower at 13 years because so many of the participants had already died.)
The findings were essentially the same in men and women and in whites and blacks. Nor could the findings be explained by socioeconomic factors (such as levels of education and income), lifestyle behaviors (such as exercise and diet) or other health-related factors, the researchers report.
Surprisingly, however, the association between a poor sense of smell and a higher risk of dying was strongest among people who were in good or excellent health at the start of the study.
A poor sense of smell is already known to be an early sign of dementia and Parkinson’s disease. It’s also known to be associated with weight loss. In the current study, dementia and Parkinson’s disease accounted for 22 percent of the deaths among those with a poor sense of smell — a figure that climbed to 30 percent when weight loss was added.
There was a modest link to deaths from cardiovascular disease, but no link to deaths from cancer or respiratory illnesses.
That left a large proportion of the higher death rate among those with a poor sense of smell unexplained.
“We don’t have a reason for more than 70 percent of the increased risk,” said Chen. “We need to find out what happened to these individuals.”
The researchers do not believe, however, that those deaths can be explained by the eating of spoiled food, gas-leak poisonings or fires — three dangers faced by people who have lost their sense of smell — because such deaths among older adults are rare.
Limitations and implications
The study comes with several important caveats. First, it was observational, so it can’t prove that an impaired sense of smell is connected to an increased risk of death. In addition, the participants’ sense of smell was tested only once. Their ability to detect odors may have been temporarily impaired at that time — or it may have changed over the course of the study. Either situation could have affected the study’s findings.
Also, the average age of the participants was 76, and more than half of them died over the 13 years, whether or not their ability to smell was good or poor. So, the absolute (as opposed to the relative) increased risk of dying for an older individual with a poor sense of smell is likely to be small.
Still, the study’s findings can’t be ignored, either, as it’s well established that a poor sense of smell can be an early sign of deteriorating health.
If you’re having trouble detecting odors, don’t panic. It could be a temporary problem, caused, for example, by a sinus or respiratory infection. Should the situation persists, however, Chen recommends that you talk to a doctor.
“It’s always prudent to talk to a physician about your health concerns,” he said.
FMI: You’ll find an abstract of the study on the website for the Annals of Internal Medicine, although the full study is behind a paywall.