In the News: A Peanut Butter Smell Test for Alzheimer's?

By Eric McDade, D.O.

Although we take it for granted, our sense of smell relies on an impressive level of complexity that not only allows us to experience the world around us, but also puts it at risk for injury through a number of different ways. Most of us are familiar with the incredible experience of being immediately transported back to a previous place or time after smelling a special scent. Researchers in Alzheimer’s dementia and other related disorders such as Parkinson’s disease and Lou Gehrig’s disease have  found that our sense of smell might be helpful in detecting brain changes associated with these and other illnesses.

Based on this, researchers led by Dr. Kenneth Heilman, professor of Neurology, and Jennifer Stamps, a graduate student in the McKnight Brain Institute Center for Smell and Taste at the University of Florida, have recently published an interesting study looking at the usefulness of peanut butter in diagnosing Alzheimer’s dementia from other types of dementias. The paper published in the Journal of Neurological Sciences, used a very simple approach.

Here’s the experiment:


The experiment was then repeated in older people in three categories: those with mild memory problems (referred to as mild cognitive impairment), those with memory problems felt to be from other dementias, and those without memory problems.

What they found was that the group diagnosed with Alzheimer’s dementia had a much greater difficulty smelling the peanut butter with their left nostril compared  to the right nostril, whereas in the normal volunteer group both sides were nearly equal in detecting the smell. Also, in about half of the group with mild cognitive impairment- which represents a group with a risk of developing dementia- they found a pattern similar to those with Alzheimer’s dementia.

Based on these findings, researchers proposed that this relatively straightforward, simple test might be useful in the clinic to confirm a diagnosis of Alzheimer’s dementia, especially early on when the symptoms are still relatively mild, and in clinics where access to more sophisticated testing is not available.  However, what was not emphasized was that there are a number of things that can affect the sense of smell and that based on this study people should not assume that a change in smell means they are developing Alzheimer’s dementia.

It is critically important to keep in mind that the sense of smell can be affected by a large number of things including medications, allergies, environmental exposures and, importantly, our sense of taste! Readers should not think that because their sense of smell has changed that they have Alzheimer dementia.

What makes this study unique and intriguing is how simple the test was and how the large differences were between the groups. However, important limitations of the study include that those diagnosed with Alzheimer’s dementia were more cognitively impaired than the other groups which could account for some of the results. Also, there was a group of patients with the opposite pattern, where the right side was more affected than the left side. Lastly, they excluded anyone that could have problems with their sense of smell for other reasons. Although the research is exciting, future research will require larger groups of people to be tested and for the diagnosis to be confirmed.

As most of us involved in dementia and neuroscience research understand, the mind is beautiful yet incredibly complex. Rarely is there a “simple” explanation or answer to a disorder as complex as Alzheimer’s. However, this study does support further research into disorders of smell in Alzheimer’s and other types of dementia. It also reminds us of the importance of identifying practical, inexpensive tests that could be used to help diagnose Alzheimer’s.

Eric M. McDade, DO, is an assistant professor of Neurology at the University of Pittsburgh School of Medicine, and associate director of the Clinical Core of Pitt’s Alzheimer Disease Research Center.  

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