A recent study has added to a growing body of evidence that loss of smell is a predictive marker for an increased risk of frailty as people age, and that testing for this as part of routine screenings could help identify risks of unhealthy ageing.
Building on previous research showing that olfactory dysfunction is a common early sign of brain-linked cognitive decline, the latest findings by a team from Johns Hopkins Medicine – using data from nearly 1 200 older adults – suggest the link to frailty is possibly not just in the brain but also in the nose itself.
If further studies affirm their conclusions, the researchers said, screening older adults’ ability to smell various scents could be as important as testing hearing and vision over time.
Results of the study, published in the Journal of Gerontology, looked at the prevalence of frailty, an age-related syndrome of physiological decline, along with two methods of assessing the ability to smell: olfactory sensitivity (the ability to detect an odour’s presence) and olfactory identification (the ability to detect and name an odour).
Olfactory identification is a central measure of smell function, which has been linked to frailty and relies on higher-order cognitive processing to interpret and classify an odour. This suggests neurological function may help to explain the relationship between smell and frailty. However, researchers say the ability to merely detect a smell without having to use higher-level neurological processes and the relationship of the ability to detect odours alone with frailty have been understudied.
“We use our sense of smell to identify the threat of a fire or to enjoy the fragrance of flowers on a spring day. But just like vision and hearing, this sense weakens as we age,” said Dr Nicholas Rowan, associate professor of otolaryngology-head and neck surgery and corresponding author of the study.
“We found that both impaired olfactory identification and sensitivity functions are associated with frailty, which is interesting because it shows it’s not just your ageing brain at work here, but it may also be something peripheral, like something at the level of your nose that is able to predict our impending frailty and death.”
Although these findings in older adults add to a body of literature suggesting the sense of smell can be a bellwether of frailty and impending mortality, he said the relationship of these unique sensory losses with unhealthy ageing over time is unclear.
However, what is clear, he added, was that common consequences of smell loss include a loss of appetite, difficulty in monitoring personal hygiene, depression, and an inability to detect toxic fumes. In older adults, this may be associated with weight loss, malnutrition, weakness, inadequate personal care and even potential injuries caused by gas leaks or fires.
In the US, the population of older adults is estimated to double in the next three decades, driving efforts to sort out which older adults are most likely to experience frailty, a strong marker of impending death compared with those without it. The new study used a standard assessment of frailty (called a Physical Frailty Phenotype, or PFP, score) that looks at five markers: weight loss, exhaustion, weakness, slow walking speed and low physical activity.
To examine the relationship between frailty and olfaction, the research team analysed data from 1 160 older adults enrolled in the National Social Life, Health and Aging Project between 2015 and 2016. The mean age was 76, and 55.7% were female. Participants were exposed to five scents to measure olfactory identification and six scents to measure sensitivity levels. Results were then matched to a subject’s frailty score.
Researchers concluded that for every one-point increase in both olfactory identification and sensitivity scores, there was a significant and meaningful reduction in frailty status, implying that improvements in smell were associated with improved health status and resilience of older results. Conversely, the worse the sense of smell, the frailer a subject was, suggesting that smell loss can be a measurable biomarker and potential risk factor for frailty in older adults.
As a matter of practical medical care, Rowan said the findings mean that smell tests could become part of routine screenings as a way to identify risk of unhealthy ageing, and a tipoff to whether additional tests of cognition and other conditions are needed.
“We already do tests to assess how well we can see or hear, and it’s just as easy to conduct a simple smell test that takes only minutes, which could potentially be used as a valuable tool to assess the risk of frailty or unhealthy ageing,” he said. “For example, if someone flunks a smell test then maybe this patient needs to improve his or her nutrition or undergo a more detailed neurological or medical workup.”
To answer this question, Rowan and his colleagues from the Johns Hopkins University Claude D Pepper Older Americans Independence Centre are investigating how more detailed smell tests may help researchers and clinicians identify physiologically vulnerable older adults. Rowan said these results are especially important in the setting of the Covid-19 pandemic, which has caused lasting smell loss for millions of poeple. “The really interesting question, though, is what happens to these novel relationships when you seek to treat the smell loss,” he said.
Study details
The Association of Peripheral and Central Olfaction With Frailty in Older Adults.
Nimesh Nagururu, Isaac Bernstein, Kristin Voegtline, Sarah Olson, Yuri Agrawal, Nicholas Rowan.
Published in The Journals of Gerontology on 11 December 2022
Abstract
Background
Olfactory impairment is increasingly recognised as a biomarker of frailty, but the relationship between olfactory subdomains that describe peripheral or central dysfunction and frailty remains unexplored.
Methods
We examined 1 160 older adults from the National Social Life, Health, and Aging Project Wave 3. Olfactory identification (OI): the ability to identify an odorant; and olfactory sensitivity (OS): the ability to detect the presence of an odorant, were assessed using 5- and 6-point measures, respectively. Frailty was operationalised as both a 37-item frailty index (FI) and the 5-item Physical Frailty Phenotype (PFP). Mixed models were fit to examine the association between OI, OS, FI, and PFP, while adjusting for demographic and clinical covariates.
Results
Participants in the most-frail PFP category had lower OI and OS scores (OI: 3.88 vs 4.19, p = .016; OS: 3.15 vs 3.47, p = .031), whereas participants in the most-frail FI category exhibited lower OI scores but not OS scores when compared to non-frail participants (OI: 3.72 vs 4.27, p = .014; OS: 3.19 vs 3.43, p = .476). Adjusted mixed models showed that a point increase in OI was associated with a lower PFP score (β = −0.107, p = .006) and FI score (β = −0.009, p = .010). A point increase in OS was associated with a lower PFP score (β = −0.058, p = .016) but not FI score (β = −0.004, p = .064).
Conclusion
Both OS and OI, predominantly peripheral and central measures of olfaction, respectively, are associated with frailty implicating olfaction as a potential biomarker and risk factor for frailty.
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