Poor sense of smell is a marker for a mortality risk in older adults

Olfactory impairment is a marker for mortality risk in older adults, with the highest risk associated with neurodegenerative mortality, a study based out of Sweden has found.While previous studies have also linked smell and mortality risk, this study expands on existing research by identifying “mediators,” including dementia and frailty, that help to explain the association, according to a news release.Sense of smell may be linked to mortality through multiple mechanisms, the authors explained in the study, which was published in JAMA Otolaryngology-Head and Neck Surgery.Directly, olfactory deficits can impair a person’s ability to detect hazards like spoiled food or natural gas, although deaths due to such incidents are rare.Indirectly, a poor sense of smell may be a marker of underlying conditions including neurodegeneration. “Olfactory impairment is closely associated with Alzheimer and Parkinson diseases, with early neuropathological changes observed in brain regions supporting the olfactory system,” the authors wrote. Olfactory deficits may also be a sign of “increased systemic inflammation, reduced neural plasticity, and diminished repair capacity, contributing to frailty and a decline in physical function and an increased vulnerability to illness and accidents,” the authors wrote. “It may also indirectly elevate mortality risk through altered eating behaviours, leading to malnutrition,” they added.It is likely that these mechanisms interact, which means olfactory impairment is potentially both a contributor to and a marker of mortality risk, according to the study.Passing the smell test: Study design and resultsThe longitudinal cohort study analyzed data from the Swedish National Study on Aging and Care in Kungsholmen. It enlisted more than 2,500 participants with a mean age of 72 years at the start of the study. Baseline assessments, which excluded patients with known dementia, took place between March 2001 and August 2004. Follow-ups with participants took place at six and 12 years. Data analysis took place between February 2024 and July 2024.The baseline assessments measured participants’ olfactory abilities using a 16-item “odour identification test.” Scents included lemon, garlic and coffee.Based on their responses, participants were categorized as anosmic (zero to six correct answers), hyposmic (seven to 10 correct answers) or normosmic (11 to 16 correct answers).The researchers found that each incorrect answer on the test was associated with an increased mortality risk of approximately 6% at six years and 5% at 12 years. At both follow-ups, the anosmic group had a nearly 70% higher risk of mortality than the normosmic group.In terms of specific causes of death associated with a poor sense of smell, the highest risk was for neurodegenerative deaths, followed by respiratory and cardiovascular deaths. Olfactory deficits were not found to be associated with cancer mortalities or deaths from other causes.At the six-year follow-up, dementia, frailty and malnutrition were “key mediators of the olfactory-mortality association.”Dementia accounted for 23% of this association, “making it the most important mediator of all-cause death.”However, at the 12-year mark, dementia accounted for only 6% of the association.“You have different disease progression types, and I think that someone in the 12-year follow-up, you still include the survivors that have a very slow disease progression and their dementia doesn’t really matter so much anymore [for the olfactory-mortality association], senior author Ingrid Ekström said in the release. “It’s more factors like frailty.”Clinical implications: The case for more routine olfactory screeningsIn addition to being associated with underlying conditions, having a poor sense of smell can be a safety issue that increases mortality risk, such as when a person cannot smell natural gas or smoke.In some instances, olfactory deficits can be “easily surmised,” according to the release paraphrasing Ekström. For instance, if a patient is showing signs of malnutrition, it is a good idea to ask them about their sense of smell.However, patients may not always realize that their sense of smell is compromised, Ekström explained.One potential solution is to implement olfactory screening practices similar to routine vision or hearing assessments, according to Ekström. These screenings should start early in life.“If we start looking at olfaction only in the older population, we don’t really know if it’s an age-related impairment or a life-long health impairment,” Ekström said.

Poor sense of smell is a marker for a mortality risk in older adults

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