An Early Warning: Sense of Smell and Dementia

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Certain smells are very recognizable: peppermint, oranges, roses just to name a few. I, like many, take the ability to smell these scents for granted; but, as Joni Mitchell and many of her followers sang, “you don’t know what you’ve got till it’s gone.” Losing the ability to detect these scents could be an accurate early warning sign of dementia.

When the sense of smell does go, it is oftentimes more than just a nuisance. Not being able to enjoy the aroma of a good meal is one thing. Not being able to smell the smoke from a fire in your home is entirely another! In between are less important, but still significant examples such as not being able to smell spoiled milk.

A diminished or lack of sense of smell has a few causes. I divide them into two categories: something blocking air from reaching the smell (olfactory) nerve that sits between the nose and the brain; and something wrong with the nerve, itself.

The first category includes most of the things that we know go wrong in the nose, like a deviated septum, polyps growing in the nose, severe allergies, etc. These are the kinds of things that docs like me have a decent chance of improving or fixing.

We know now that when the elderly lose their sense of smell, their risk of having dementia is THREE TIMES HIGHER.

The second category is much harder to do anything about. A common thread among people in this category is that they had a seemingly mild cold for a day or two, nothing serious. But soon afterward, they noticed that their sense of smell was severely diminished or completely gone. This realization usually comes several days to weeks after the mild upper respiratory infection, so it’s sometimes hard to put two and two together. In this situation, we will sometimes try a short dose of steroids to decrease inflammation and try to jumpstart some recovery, but the results of this treatment are mixed.

When we are talking about the senior population, the conversation about loss of smell changes a bit. We know now that when the elderly lose their sense of smell, their risk of having dementia is THREE TIMES HIGHER. This is a big deal. There was a study done that tested sense of smell in seniors and then checked for dementia five years later. Those who could only identify two out of five scents developed dementia 80% of the time – a huge correlation.

In science, there is a difference between causation and correlation. There is no evidence that loss of the olfactory nerve causes dementia. It is more likely that the loss of function is correlated with loss of nerve tissue in other parts of the brain. It is similar to when a car is at high mileage and the alternator goes out, then the transmission soon after. The alternator failure did not cause the transmission failure, but when it goes out, it is a predictor that, because of high mileage, the tranny is at risk, also.

So, no, I can’t fix someone’s nose to prevent dementia! But detecting that someone has a decreased sense of smell is a great way to warn them about the high likelihood of dementia and to engage them in hobbies like reading and problem-solving to help keep the brain sharp. Being vigilant about the early signs of the significant health issue to come can help people stay in their prime for many more years.

 

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