09 June 2015

Smelling Sense Addendum

I withheld a few items from last Friday’s blog post, Smelling Sense. For one, I didn’t think it was necessary to devote space to the importance of smell for detecting smoke or gas and the consequent need to compensate for olfactory decline or impairment with functioning alarms. Other items, I just didn’t want to spoil your weekend.

Well, it’s Tuesday and I hope you had a pleasant weekend.

Olfaction, Alzheimer’s and Parkinson’s Disease

The loss of the sense of smell may be attributed to various causes, yet there is growing evidence that a decreased ability to correctly identify odors is a predictor of cognitive impairment and an early clinical feature of Alzheimer's. Similarly, olfactory dysfunction, which is commonly associated with Parkinson's disease, is increasingly recognized as an early symptom in the development of the disease.

If you’re on the elderly side and if your sense of smell isn’t up to snuff for reasons unknown, should you panic? Of course not; however, it would be a good idea to have it checked.

And that’s the good news.

Olfaction and Death

The not so good news, based only on a single 2014 study from the University of Chicago, is that olfactory dysfunction may portent death.

To arrive at that conclusion, the investigators gave a smell test with five common scents (rose, leather, orange, fish, and peppermint) to a nationally representative sample of 3,005 volunteers, aged 57 to 85. Five years later, they followed up to determine if the volunteers were still alive. Missing data and undetermined volunteer mortality status reduced the final data set to 2,918 live or deceased volunteers. 

Though not used in the University of Chicago study, the University of Pennsylvania Smell Identification Test is a commonly employed, self-administered test with 40 scratch-and-sniff odors released by pencil tip. The test is available in 15 languages from Sensonics International. (Photo from sensonics.com/smell-identification-test-international-versions-available.html)
The investigators used the data to develop a comprehensive predictive model that controlled for demographics and health factors. Their model estimated that those who could identify no more than one scent (3.5% of the volunteers) were three times more likely to die within 5 years than those who could identify at least 4 scents (nearly 78% of the volunteers). Even those who could identify 2 or 3 scents (nearly 20% of the volunteers) were at elevated risk.

Do the study results mean you’re going to die if you don’t do well on a smell test? No. But if cell regeneration is declining in the olfactory system, it may also be happening in other parts of the body. As noted above for Alzheimer's and Parkinson’s, an impaired sense of smell warrants medical attention.


News release from 2014 Alzheimer's Association International Conference: www.alz.org/aaic/releases_2014/sun-830am-smell-eye-tests.asp
Paper on olfaction and Parkinson’s disease in PLOS ONE journal:
Paper on olfactory dysfunction predicting death in PLOS ONE journal and article on LiveScience website:
Review paper on olfaction and age in Frontiers in Psychology journal: journal.frontiersin.org/article/10.3389/fpsyg.2014.00020/full

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