Can Bitter Taste Perception Predict COVID Outcomes?
This study in JAMA Network Open looked at people before they got the COVID-19. This is not a study that says that the degree to which you lose taste after you get COVID tells you how sick you'll get but rather can your sense of taste predict your risk of getting COVID-19.
Okay, here's what you need to know.
There are certain genetic traits that change how you perceive certain tastes. You may have heard that some people have a mutation that makes delicious cilantro taste like horrible soap. My condolences to these poor souls who can never truly enjoy guacamole.
But that's not the only taste-linked gene. The gene of interest in this study is called T2R38. It is a bitter taste receptor, and there are essentially two flavors of the gene: one called PAV and one called AVI.
If you inherit two copies of this gene PAV, certain chemicals like propylthiouracil, that is found in brussel sprouts and coffee, taste obnoxiously bitter to you. If you inherit two copies of AVI gene, you don't taste it at all. And if you have one copy of each, you're somewhere in the middle.
What does this have to do with COVID?
Well, bitter taste receptors are special because they don't just live on the tongue. T2R38 is expressed throughout the respiratory tract and, when it is activated, causes cells in those areas to release nitric oxide. That nitric oxide causes the cilia in your nose to beat faster, getting the offensive particles out of there.
The idea is that, in general, bitter is a sign that we shouldn't eat something. And what's good for the tongue is good for the respiratory passages as well. These receptors may form part of the innate immune system. There is at least some biologic plausibility that dysfunction of these receptors might increase the risk for COVID.
Researchers took 1935 people who had been exposed to COVID (they were mostly healthcare workers) and tested their ability to taste a bitter chemical. About a quarter were found to be "supertasters"; they had a strong reaction. A quarter had no reaction, and the rest were somewhere in the middle. In this study they also genetically tested the subjects for this taste gene. 3 of the supertasters however did not perform well on the taste test, but they were older.
If this is all true, it would make your ability to taste propylthiouracil one of the strongest predictors of COVID-19 risk.
One note, your ability to taste declines with age. This was demonstrated in the study; non-tasters tended to be a bit older. Smoking also decreases your ability to taste.
So how do you test if you have the the genetic T2R38 receptor? Supertasters at this gene locus find cruciferous vegetables like brussel sprouts pretty bitter. Also, if you are a two creams two sugars coffee drinker, you likely find the taste of coffee bitter. So if you, like me, think Brussels sprouts are the worst, and love a loaded latte, well, for this pandemic at least, that could be pretty sweet.
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