Sleep apnea and sense of smell

Are your senses intact? In other words, can you see well, taste well, hear well, and smell well? We have previously reported that untreated sleep apnea has been linked with eye issues (glaucoma, increased eye pressure, etc.), but not much has been covered on the other senses. A recent investigation set out to determine whether smell issues (which people might not even realize that they have) are related to untreated sleep apnea. Given that the sense of taste is basically just the sense of smell, sleep apnea affecting smell would mean sleep apnea affecting taste as well.

Investigating this issue required a few different sets of data. First, sleep apnea status was needed. In order to obtain this, the research team, based in Turkey, had participants undergo overnight sleep studies to assess the presence and severity of sleep apnea. Participants were split into four diagnostic groups: those without sleep apnea, those who snored but did not have sleep apnea, those with mild obstructive sleep apnea (OSA) and those with severe sleep apnea (more than 30 apneas and/or hypopneas per hour). Each individual also completed a sleepiness scale to report how sleepy they normally feel. Next, participants underwent an otorhinolaryngologic examination, which included tests such as the Muller maneuver with flexible nasopharyngoscopy. These tests assessed the integrity and health of the ear, nose, and throat system. Finally, participants underwent a smell test using Sniffin’ Sticks (seriously). These sticks include 12 common odors that the participant must attempt to identify. The scores were compared between sleep apnea groups.

Those without sleep apnea were able to identify the most odors, whereas those with severe sleep apnea correctly identified the fewest odors. A relationship was found between odor scores and number of apneas per hour, such that more apneas meant less odor discrimination. This relationship was also present for odor scores and the amount of oxygen in the blood during sleep, which is lowered when apneas occur. Lower oxygen in the blood meant worse smelling. What’s more, the sleepier the individuals rated themselves, the poorer their odor discrimination. Interestingly, odor scores were also correlated with physical parameters of the upper airway, such that a narrower airway limited odor identification. Clearly, an investigation is needed to determine whether treating sleep apnea reverses this lack of smell. Perhaps eliminating apneas, which would also increase blood oxygen levels during sleep, could help raise those Sniffin’ Sticks scores.

This study has real-world implications for those with sleep apnea. If you’ve ever had a cold with a stuffy nose, you may have noticed that your sense of taste becomes blunted without your taste of smell. Untreated sleep apnea may lead to an eternity of blunted senses! Stay treated, and stay smelling!

Source: Günbey, E., Güzel, A., Karl, R., & Ünal, R. (2015). The relationships between the clinical and polysomnographic findings and the olfactory function in patients with obstructive sleep apnea syndrome. Sleep and Breathing, 1-7.


Janna Mantua

Author

Janna is a PhD Student / Graduate Research Assistant at University of Massachusetts Amherst with a background in clinical sleep research and psychology. Janna Mantua is a PhD student in the Behavioral Neuroscience department at the University of Massachusetts. Her research focuses on sleep and aging, with specific projects on cognitive health, inflammation, memory formation, and neuroimaging. Prior to her PhD work, Janna was involved in research on sleep apnea and cognitive decline at the NYU Sleep Disorders Center.



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