Losing one's sense of smell, a condition known as anosmia, becomes more common as we age. Anosmia robs us of the rich sensory experience of detecting pleasing or noxious odors. But losing your sense of smell may signify something more ominous - evidence suggests it can presage cognitive decline and neurodegenerative diseases like Alzheimer’s and Parkinson’s. Could restoring a faded sense of smell help protect the aging brain? A new study suggests that may just be the case.
Researchers at UC Irvine had 43 healthy adults between the ages of 60 and 85 undergo a simple daily "smell training" regimen for 6 months. Half the group received an odor diffuser and 7 small vials containing different pleasant essential oils, with instructions to diffuse a different oil in their bedroom each night during sleep. The other half used an identical diffuser with barely detectable concentrations of fragrance as a control.
Mean difference between pre-and post-measurements for the Rey Auditory Verbal Learning Test (RAVLT – A5). Statistically significant difference between groups using an ANOVA with repeated measures (p = 0.02).
At the end of the study, the smell training group showed significant improvement in their ability to recall a list of words - a test sensitive to age-related memory changes. Meanwhile, the control group's performance declined slightly. Alongside this cognitive boost, imaging of a brain structure called the uncinate fasciculus showed evidence of enhanced structural plasticity selectively in the smell training group.
The uncinate fasciculus is a curved bundle of nerve fibers connecting areas of the temporal lobe important for memory and emotion to frontal lobe regions that control executive functions like attention and planning. Damage to this structure is seen in various neurodegenerative diseases. Smell training at night may help preserve or even strengthen this vulnerable pathway, and exhibit exciting therapeutic implications.
Uncinate Fasciculus
But how does merely sniffing rose or lemon scent in one's sleep contribute to these benefits?
Studies in rodents show olfactory enrichment enhances neuroplasticity and stem cell proliferation in brain regions critical for learning and memory. Unlike other senses, smell has direct access to these areas rather than needing to route through intermediary hubs. Constantly sniffing novel odors may drive cellular remodeling to refresh associated circuits. Perfume exposure additionally boosts time spent in restorative slow-wave sleep.
However, demanding smell training regimens require repeatedly sniffing many odors daily, as shown successfully in some trials, and may be impractical for broader adoption. This study demonstrates that even minimal smell exposure during sleep can pay measurable cognitive dividends. Beyond novel scents, sleep itself likely helped cement the olfactory memories and channel them into durable traces. The elegance of passive overnight exposure is that it requires no added effort.
That said, with only 20 odor-enriched participants assessed, study numbers limit confidence in generalizing the findings. And with by far the majority of subjects being women in their early 60s, results may not apply equally across genders or very old age. There are likely also responders and non-responders depending on individual differences in smell ability or brain integrity. Follow-up trials are underway investigating biological markers that might help predict who will gain a cognitive boost from this inexpensive intervention.
Given population aging and the immense toll impending rises in dementia prevalence threaten to take on strained healthcare systems and caregiver quality of life, there is an urgent appeal for preventative solutions with low barriers to adherence. If confirmed by larger-scale testing, supplying elderly individuals with simple smell diffusers and a variety of scented oils may represent one route to fortifying vulnerable nervous systems against imbalance and decay. Though this isn’t a catch-all remedy, nightly scent exposure could contribute to the diverse lifestyle modifications needed to prolong cerebro-cognitive health with advancing years.
Tracking longitudinal outcomes beyond 6 months will also reveal whether observed neural changes foster sustained protection or merely transient improvement. It will additionally help establish guidelines around the necessary duration and frequency for maximum brain benefit.
If you want to make a smaller change to potentially boost your brain health, this study lends some support to actively sniffing different aromatic items throughout the day and sufficiently ventilating sleeping areas with pleasant ambient fragrances overnight. Those experiencing substantial smell deficits may additionally inquire with physicians about targeted smell retraining therapy to counteract the winding down of underutilized olfactory networks. Together these habits may aid in preserving our capacity for rich aromas to spark memories and emotions - and counteract potential cognitive decline.
So go ahead, take a moment to stop and smell the roses. With time your brain may thank you for it!