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Scientists Reveal Surprising Link Between Odor Detection and Memory

Scientists Reveal Surprising Link Between Odor Detection and Memory about undefined
Walk outside, what do you smell? Perhaps it’s the lovely rose bush blooming nearby. Or maybe it’s an unpleasant aroma, such as manure or air pollution. The important part is that your sniffer is still up to snuff. You see, according to some researchers, older adults who can still identify distinctive smells may maintain sharper memories than their peers as they age. Let’s take a closer look... A slew of studies over the last 20 years have shown a connection between poor odor detection and poor cognitive function. And now, a study from University of California, San Francisco (UCSF) further explores this link. Researchers followed 1,800 participants aged 70 and older for up to ten years to see if sensory decline was related to the development of dementia. While previous research centered on the link between dementia and individual senses, the UCSF researchers' focus was on the effects of multiple impairments in sensory function.1 Here’s what they found: After examining the effect of the senses of touch, hearing, vision and smell on dementia development, the authors reported that sense of smell was most important to maintaining a sharp memory. In fact, the authors discovered that participants whose sense of smell dipped by ten percent had a 19 percent higher chance of dementia versus only a one to three percent increased risk for dementia with corresponding declines in vision, hearing and touch.

Why is Smell so Important? 

Study author Willa Brenowitz, PhD, of the UCSF Department of Psychiatry and Behavioral Sciences, explained that, unlike hearing and vision loss, loss of smell is an indicator of what’s going on in the brain. “The olfactory bulb, which is critical for smell, is affected fairly early on in the course of the disease,” Dr. Brenowitz explains. “It’s thought that smell may be a preclinical indicator of dementia, while hearing and vision may have more of a role in promoting dementia.” She notes that researchers believe that hearing and vision loss may accelerate cognitive decline in a less direct way by increasing “social isolation, poor mobility and adverse mental health.” Additionally, the researchers found that those people with good multisensory function were more likely to be healthier than their counterparts. This suggests that healthy lifestyle choices may play a role in reducing dementia risk. Dr. Brenowitz published the study in Alzheimer’s and Dementia: The Journal of the Alzheimer’s Association.2

What Causes Loss of Smell? 

Some studies indicate that your sense of smell is influenced by the presence of damaging beta amyloid protein in areas of the brain that are in charge of olfactory tasks.3 So, it could be that the loss of smell is like a canary in a coal mine, occurring before symptoms of cognitive decline can be detected. One of the flies in the ointment is that as people age, their sense of smell naturally declines. Therefore, this fact needs to be taken into account in future research.4 Still, the preponderance of evidence points to a significant link between a poor sense of smell and cognitive decline.5

Twice the Dementia Risk 

Another study examined 3,000 adults aged 57 to 85 with normal cognition over the course of five years.6 Researchers found that a decreased ability to tell the difference between odors was strongly associated with more than twice the risk of developing dementia. That’s significant! In a smaller study researchers tested participants’ cognitive function as well as their ability to detect smells at the beginning of the study, and then annually thereafter.7 The participants who struggled to detect odors experienced declining scores on the cognitive function tests in the ensuing years. Simply put, their inability to identify odors predicted who would go on to develop signs of mild cognitive impairment (MCI), which is often a precursor to Alzheimer’s disease.

Stop and Smell the Roses 

Should we be taking a sniff test to determine if dementia is on our horizon? I’m not sure if the evidence justifies that just yet. However, in the future it’s possible that a smell test might be included in every dementia screening. In the meantime, I suggest turning your attention to what you can do today to reduce your risk of developing dementia and a host of other illnesses of aging. That means getting regular exercise and eating a healthy diet rich in fresh fruit, green leafy vegetables, lean meats and minimizing processed foods and sugar. That also means maintaining your social connections and your engagement with the world around you. And of course, managing your stress level and getting plenty of good sleep.
  1. https://www.ucsf.edu/news/2020/07/418116/older-adults-who-can-really-smell-roses-may-face- lower-likelihood-dementia 
  2. https://alz-journals.onlinelibrary.wiley.com/doi/10.1002/alz.12134 
  3. Kreisl WC, Jin P, Lee S, et al. Odor identification ability predicts pet amyloid status and memory decline in older adults . J Alzheimers Dis. 2018;62(4):1759-1766.
  4. Sun GH, Raji CA, Maceachern MP, et al. Olfactory identification testing as a predictor of the development of Alzheimer's dementia: a systematic review. Laryngoscope. 2012;122(7):1455-1462. doi:10.1002/lary.23365
  5. Sohrabi HR, Bates KA, Weinborn MG, et al. Olfactory discrimination predicts cognitive decline among community-dwelling older adult. Transl Psychiatry. 2012;2(5):e118. 2012 May 22. doi:10.1038/tp.2012.43
  6. Adams DR, Kern DW, Wroblewski KE, et al. Olfactory dysfunction predicts subsequent dementia in older u.s. adults . J Am Geriatr Soc. 2018 Jan; 66(1): 140–144.
  7. Wilson RS, Schneider JA, Arnold SE, et al. Olfactory identification and incidence of mild cognitive impairment in older age . Arch Gen Psychiatry. 2007;64(7):802-808.

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