A new Michigan State University study suggests that older adults with poor sense of smell may see an almost 50% increase in their risk of dying within 10 years – surprisingly in healthier individuals.
“Poor sense of smell becomes more common as people age, and there’s a link to a higher risk for death,” said Honglei Chen, an epidemiologist who’s focused his research on this sensory deficit in older adults. “Our study is the first to look at the potential reasons why it predicts a higher mortality.”
Using data from the National Institute on Aging’s Health ABC study, Chen and his research team reviewed information from almost 2,300 participants between 71 and 82 years old over a 13-year period. Participants included men and women, black and white, who completed a smell test of 12 common odours. Researchers then classified participants as having good, moderate or poor sense of smell.
Compared with older adults with a good sense of smell, those with poor smell were at a 46% higher risk for death at 10 years and 30% at 13 years.
Results were minimally affected by sex, race or other demographic and lifestyle factors. However, the surprising revelation was that the healthier participants at the start of the study were found to be largely responsible for the higher risk.
Poor sense of smell is known as an early sign for Parkinson’s disease and dementia and is associated with weight loss. However, these conditions only explained 28% of the increased risk, leaving most of it unexplained.
“We don’t have a reason for more than 70% of the increased risk. We need to find out what happened to these individuals,” said Chen, who plans to pursue the mystery in future studies.
He added that poor sense of smell may be an early and sensitive sign for deteriorating health before it’s even recognized in the doctor’s office. “It tells us that in older adults, impaired sense of smell has broader implications of health beyond what we have already known,” Chen said. “Incorporating a sense of smell screening in routine doctor visits might be a good idea at some point.”
So, what should people do if they think they’re having trouble smelling? Talk to a doctor. “It’s always prudent to talk to a physician about your health concerns,” he said.
Background: Poor olfaction is common among older adults and has been linked to higher mortality. However, most studies have had a relatively short follow-up and have not explored potential explanations.
Objective: To assess poor olfaction in relation to mortality in older adults and to investigate potential explanations.
Design: Community-based prospective cohort study.
Setting: 2 US communities.
Participants: 2289 adults aged 71 to 82 years at baseline (37.7% black persons and 51.9% women).
Measurements: Brief Smell Identification Test in 1999 or 2000 (baseline) and all-cause and cause-specific mortality at 3, 5, 10, and 13 years after baseline.
Results: During follow-up, 1211 participants died by year 13. Compared with participants with good olfaction, those with poor olfaction had a 46% higher cumulative risk for death at year 10 (risk ratio, 1.46 [95% CI, 1.27 to 1.67]) and a 30% higher risk at year 13 (risk ratio, 1.30 [CI, 1.18 to 1.42]). Similar associations were found in men and women and in white and black persons. However, the association was evident among participants who reported excellent to good health at baseline (for example, 10-year mortality risk ratio, 1.62 [CI, 1.37 to 1.90]) but not among those who reported fair to poor health (10-year mortality risk ratio, 1.06 [CI, 0.82 to 1.37]). In analyses of cause-specific mortality, poor olfaction was associated with higher mortality from neurodegenerative and cardiovascular diseases. Mediation analyses showed that neurodegenerative diseases explained 22% and weight loss explained 6% of the higher 10-year mortality among participants with poor olfaction.
Limitation: No data were collected on change in olfaction and its relationship to mortality.
Conclusion: Poor olfaction is associated with higher long-term mortality among older adults, particularly those with excellent to good health at baseline. Neurodegenerative diseases and weight loss explain only part of the increased mortality.
Bojing Liu; Zhehui Luo; Jayant M Pinto; Eric J Shiroma; Gregory J Tranah; Karin Wirdefeldt; Fang Fang; Tamara B Harris; Honglei Chen