The Nose Knows: Olfaction's Role in Cognitive Health and Longevity
The sense of smell, or olfaction, might be more than just a way to enjoy your favorite fragrances. It could be a key player in cognitive health and longevity. The ability to identify smells has been suggested as an early indicator of cognitive decline. But how does olfaction play a role throughout various cognitive states and even death?
The research delved into this question using data from the Rush Memory and Aging Project. The olfactory ability of participants was assessed using the Brief Smell Identification Test, while their cognitive states were determined using a three-step neuropsychological diagnostic protocol. The researchers found that higher olfactory scores were associated with a reduced risk of transitioning from unimpaired cognition to mild cognitive impairment (MCI), and from MCI to dementia. Interestingly, higher olfactory scores were also associated with a greater likelihood of transitioning backward from MCI to unimpaired cognition.
These findings suggest that a good sense of smell is associated with a decreased risk of transitioning to impaired cognitive states. However, the association between olfaction and mortality seems to occur primarily through the pathway of neurodegeneration. This means that the sense of smell might be an important factor to consider in the pursuit of cognitive health and longevity.
Article Information
Transitions Between Mild Cognitive Impairment, Dementia, and Mortality: The Importance of Olfaction
Published on J Gerontol A Biol Sci Med Sci.Jamie E Knight et al.
Abstract
Background: The existing literature suggests that impaired olfaction may be an early marker for cognitive decline. Tracking the earliest stages of the progression to dementia is paramount, and yet the importance of olfactory ability throughout cognitive states and death remains unclear.
Methods: Drawing data from the Rush Memory and Aging Project (N = 1 501; 74% female), olfactory ability was assessed using the Brief Smell Identification Test (range = 0-16), while cognitive states (unimpaired, mild cognitive impairment [MCI], and dementia) were determined using a 3-step neuropsychological diagnostic protocol at up to 15 annual occasions. Multistate survival models simultaneously estimated the association of olfactory ability on transitions through cognitive states and death, while multinomial regression models estimated cognitively unimpaired and total life expectancies.
Results: Higher olfactory scores were associated with a reduced risk of transitioning from unimpaired cognition to MCI (hazard ratio [HR] = 0.86, 95% confidence interval [CI] = 0.82-0.88) and from MCI to dementia (HR = 0.89, 95% CI = 0.86-0.93), indicating that 1-unit increase in olfactory scores was associated with an approximate 14% and 11% reduction in risk, respectively. Additionally, higher olfactory scores were associated with a greater likelihood of transitioning backward from MCI to unimpaired cognition (HR = 1.07, 95% CI = 1.02-1.12). Furthermore, higher baseline olfactory scores were associated with more years of longevity without cognitive impairment. However, olfaction was not associated with the transition to death when accounting for transitions through cognitive states.
Conclusions: Findings suggest that higher olfactory identification scores are associated with a decreased risk of transitioning to impaired cognitive states and that associations between olfaction and mortality may occur primarily through the pathway of neurodegeneration.
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