Introducing the left-right nostril peanut butter test for Alzheimer’s Disease

I don’t know whether I love this story more because it involves peanut butter (yum!) or because it may give us a brilliant new way to diagnose Alzheimer’s Disease (AD) that’s cheap, simple and effective (as opposed to current tests, which are invasive, expensive and of limited utility and availability). University of Florida researchers Jennifer Stamps, Linda Bartoshuk and Kenneth Heilman have given us the left-right nostril difference AD test.

Patients with probable AD (based on neurological tests), patients with other types of dementia and healthy controls were asked to breathe normally while closing their eyes and mouths and blocking one nostril. Meanwhile, an open pot of peanut butter was slowly moved up a ruler toward the person’s nose. Each participant was asked to report exactly when he or she first noticed a new odor, and the distance from pot to nostril was marked. The test was then repeated with the other nostril.

Credit: UF Health 

Everyone detected the peanut butter at about the same distance from their right nostrils (15-18 cm) and everyone except probable AD patients detected the odor at about the same distance from their left nostrils (15-20 cm). However, probable AD patients could not detect the peanut butter with their left nostrils until it was only 5 cm away. 

Thus, patients with probable AD not only had a smell deficit in their left nostrils but, more importantly, showed a huge difference between their two nostrils that was not seen in other groups, including people with non-AD dementia. That left-right nostril difference was at least 5 cm and, in three quarters of patients, more than 10 cm. Intriguingly, the size of the left-right difference seemed to track with the severity of the AD symptoms.

Before you start waving jars of peanut butter under your elderly relatives' noses, you should be aware of a couple of caveats. First, I hope I’ve made clear that these tests were done on people with probable AD. Until AD has been confirmed in the test subjects, we can’t be sure that’s what the researchers have been diagnosing. Second, this was a very small study including only 18 people in the AD group. And finally, there’s nothing magical about peanut butter. Okay, there is, but not for the purposes of this medical test. Peanut butter just happens to be a cheap, strong, familiar odor.

If further studies do confirm these findings, this would be an amazing tool for doctors. It may even be possible to use the left-right nostril test to diagnose AD much earlier than conventional neurological screenings can. 

One more thing. If you want to repeat this experiment on yourself (and who doesn’t!) try to follow the examiners’ example and pick a lab partner who does not know whether you exhibit any signs of dementia.

Stamps JJ, Bartoshuk LM, & Heilman KM (2013). A brief olfactory test for Alzheimer's disease. Journal of the neurological sciences, 333 (1-2), 19-24 PMID: 23927938.