Poor olfaction linked to long-term mortality risk in older adults

Poor olfaction is associated with risk for long-term mortality in older adults, according to a new study.

Researchers performed a community-based prospective cohort study in two U.S. communities to determine the potential relationship between poor olfaction and death in older adults. Participants in Pittsburgh, Pa., and Memphis, Tenn., were eligible for inclusion if they had no difficulty walking a quarter-mile, climbing 10 steps, or performing activities of daily living; had not received active cancer treatment in the previous three years; and did not plan to move away from the study area in the next three years. A Brief Smell Identification Test (BSIT) was administered at baseline, and all-cause and cause-specific mortality were assessed 3, 5, 10, and 13 years later. (Scores on the BSIT range from 0 to 12, with higher scores indicating better olfaction. The study authors defined scores of 0 to 8 as poor, 9 to 10 as moderate, and 11 to 12 as good.) Results were published April 30 by Annals of Internal Medicine.

A total of 2,289 adults ages 71 to 82 years were assessed at baseline. Of these, 37.7% were black and 51.9% were women. By year 13, 1,211 participants had died. Cumulative risk for death was 46% higher in those with poor olfaction versus those with good olfaction at year 10 and 30% higher at year 13 (risk ratios, 1.46 [95% CI, 1.27 to 1.67] and 1.30 [95% CI, 1.27 to 1.67]), respectively. Associations were similar for men and women and for black and white participants. However, participants with poor olfaction who reported excellent to good health at baseline had a higher risk for death, while those with poor olfaction who reported fair to poor health at baseline did not (10-year mortality risk ratios, 1.62 [95% CI, 1.37 to 1.90] vs. 1.06 [95% CI, 0.82 to 1.37], respectively). When cause-specific mortality was analyzed, an association was seen between poor olfaction and death from neurodegenerative and cardiovascular diseases. Overall, 22% of the higher 10-year mortality among patients with poor olfaction was due to neurodegenerative diseases and 6% was due to weight loss, the authors determined.

Data on change in olfaction over time were not collected, and the results may not be generalizable to younger adults or those less functional than the study participants, among other limitations, the authors noted. However, they concluded that their work offers clear evidence that poor olfaction is associated with long-term mortality in older adults. “This elevated risk can be only partially explained by dementia or Parkinson disease and weight loss, indicating that some health consequences of poor olfaction in the context of aging are unknown,” the authors wrote. “Future studies should investigate olfactory impairment as a general marker of aging to better understand its health implications and associated mechanisms in the broadest sense.”

An accompanying editorial said that the study provides additional support for a relationship between olfactory decline and unintentional weight loss, dementia risk, and death. Hyposmia and weight loss are both often seen before a diagnosis of Alzheimer dementia, and olfactory cues can affect eating and consequently energy balance and weight, the editorialists noted. However, they said, older adults are often unaware that their olfaction is declining and results of objective testing often differ widely from self-reported olfactory function.

“We note the challenges of using olfactory loss as a potential predictor of neurodegenerative disease: Most older adults show unawareness of decline, and olfaction is rarely tested in clinical practice,” the editorialists wrote. “We look forward to further observational and intervention research to inform whether and how assessment of smell should be incorporated into routine clinical practice.”

ACP Internist covered olfactory disorders in its March 2019 issue.