Summary: Poor olfaction is correlated with higher long-term mortality in older adults, particularly in those with good health at baseline. Dementia, Parkinson’s disease and weight loss may be possible drivers for the higher mortality rates, but around 70% of cases are unexplained.
Source: American College of Physicians
Poor sense of smell may be an early warning for poor health in older age that goes beyond neurodegenerative diseases. In fact, dementia or Parkinson disease explained only 22 percent of the higher death risk and weight loss 6 percent, leaving more than 70 percent of the higher mortality associated with poor sense of smell unexplained. Findings from a prospective cohort study are published in Annals of Internal Medicine.
Many studies with 5 years or less of follow up have shown an independent association between olfactory impairment and increased all-cause mortality among older adults. However, these studies did not examine whether there are differences by race or sex or the factors that might explain the relationship.
Researchers from Michigan State University studied more than 2,000 adults aged 71 to 82 years to determine the relationship between poor sense of smell and mortality and to investigate potential explanations for the connection. Participants completed a Brief Smell Identification Test (BSIT) of 12 common odors and were asked to identify each odor from 1 of 4 options. Each correct response was given a point.
Using the BSIT scores, the researchers classified the participants as having good, moderate, or poor sense of smell.
The researchers found that poor olfaction was associated with 46 percent higher mortality at year 10 and 30 percent higher mortality at year 13 compared with good olfaction. The association was robust and could not be explained by measured confounders, such as demographic characteristics, lifestyle, and comorbid conditions.
Furthermore, the association was present in both men and women and in both black and white participants, suggesting broad generalizability.
The association, however, was largely limited to participants who reported good-to-excellent health at study baseline, suggesting poor sense of smell may be an early and sensitive marker for unrecognized deteriorating health among older adults.
Relationship Between Poor Olfaction and Mortality Among Community-Dwelling Older Adults: A Cohort Study
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.
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.
Primary Funding Source: National Institutes of Health and Michigan State University.