Loss of smell linked to elevated mortality risk

Loss of smell, or olfactory dysfunction, may indicate an elevated risk for 5-year mortality, according to research published in JAMA Otolaryngology-Head & Neck Surgery.

“Poor olfactory function has been directly implicated in malnutrition, decreased safety and overall worse quality of life,” Janet S. Choi, MD, MPH, a resident in the department of otolaryngology at the USC’s Keck School of Medicine, and colleagues wrote. “It is responsible for more than 200,000 physician visits per year, representing a significant public health burden.”

Choi and colleagues conducted a cohort study of adults aged 40 years or older who participated in the 2013-2014 National Health and Nutritional Examination Survey and had information available regarding their olfaction and mortality. Olfaction was evaluated through self-reports from participants and a smell test, and researchers used the National Death Index through February 24, 2019, to identify mortalities.

A total of 3,503 participants were included in the study. Of those, 13.5% (95% CI, 11.0-16.0) had olfactory dysfunction based on results of a smell test, and 21.6% (95% CI, 18.9-24.2) had self-reported olfactory dysfunction.

The researchers determined that each 1-point decrease in smell test score led to an 18% (95% CI, 7-29) increase in risk for mortality.

In a subgroup analysis based on participant age, Choi and colleagues found that this risk was significant in adults aged 65 years and older, but not in those aged 40 to 64 years.

The researchers also determined that there was no association between self-reported olfactory dysfunction and risk for mortality.

After adjusting for cognitive assessment battery and depression in older adults, Choi and colleagues found there was still an association between objective measured olfactory dysfunction and mortality (HR = 1.18; 95% CI, 1.01-1.37).

Choi and colleagues noted that as they found that olfaction was associated with mortality independently from cognitive function, there may be other mechanisms leading to this association.

They suggested that injury to the olfactory nerve from a virus, bacteria or toxins may have also caused injury to other organs that may have then led to an increased risk for mortality. Another potential consideration, they said, is that olfactory dysfunction may indicate advanced physiological aging.

“Detection of olfactory dysfunction, especially among older adults, suggests that further workup for malnutrition, depression and neurodegenerative disease may be needed,” Choi and colleagues wrote. “Adults with known olfactory dysfunction should be more cautious of life-threatening situations because they are unable to smell danger signals in the household environment.”