In a preprint* released today, Polish researchers uncovered more specific aspects of the taste disorder caused by COVID-19, showing it especially blunts the perception of sweetness at low concentrations of sugar.
I personally find this very interesting because it adds to the data that are slowly but steadily swaying me toward the belief that I may myself have gotten COVID-19 in early February, dismissing it at the time as the flu.
The researchers studied 85 male students from a university in Warsaw, mostly in their twenties. They had been tested for COVID-19 after an outbreak was discovered, and all students were isolated from one another following the testing. 34 of the subjects included had tested negative for COVID-19, while 52 had tested positive.
They gave them a questionnaire, and also had them take tablets with various concentrations of sweet (sucrose), sour (ascorbic acid), salty (salt), and bitter (grapefruit extract) substances. The subjects then reported what the tablets tasted like.
The strongest taste finding was that 71% of the COVID-19-positive subjects could not distinguish the lowest tested concentration of sucrose, 40 mg/mL, as sweet. By contrast, only 39% of COVID-negative subjects failed to distinguish this concentration as sweet. At the highest concentration, 106.4 mg/mL, zero of the negative subjects had any trouble distinguish it as sweet, while 6 of the 52 (11%) positive subjects still could not distinguish it as sweet.
While there was a general tendency for deficiencies in other tastes to be more common in positive subjects than negative subjects, they were not statistically significant and only small numbers of subjects failed to make the distinctions.
If subjects were considered likely COVID-19 patients when they reported loss of smell, loss of taste, or fever, OR if they could not detect sweetness at 40 mg/mL sucrose, these criteria would have a sensitivity of 94% and a specificity of 55%. That the test has close to 100% sensitivity means it hardly misses any of the COVID-19 patients; that it has 55% specificity means it has a fairly high false positive rate, capturing COVID-19-negative people almost half the time.
If they used inability to taste sweetness at the highest concentration tested, 106.4 mg/mL, or inability to taste saltiness att the two lowest salt concentrations (13.5 or 17 mg/mL), the specificity increased to 100% but the sensitivity dropped to 34%. That means the test is very good at ruling out negative subjects but not very good at capturing all the positive subjects.
They considered the first approach good for screening and the second approach good for diagnosis when other diagnostic methods are unavailable.
What I find most interesting about this is that I developed what seems like a similar taste disorder when I got terribly sick in early February. My girlfriend and I had traveled by flight that weekend. Before we left, she and some of her girlfriends had been exposed to a male friend who was very sick and had a terrible cough. None of the girls got more than a little cough. The day we returned from our trip, I started getting sick. What followed was the most sick I'd been in at least twenty years. I had a fever for the first time that I could remember in 20 years. My exposure could either have been from my girlfriend or from someone on the flight.
I didn't own a thermometer at that point, but I had a terrible fever as judged by my skin feeling hot and suffering from terrible chills. There were several days where I could barely bring myself to get up out of bed or off the couch.
One of the most unusual features was that my tastes were fundamentally altered toward needing things to be sweet. There were three days where I couldn't eat normal food. Things I usually crave, such as coffee and Gerolsteiner mineral water, tasted disgustingly bitter to me. I was suffering from terrible dehydration, and I was only able to get water down when I started using LMNT, which is a salt-heavy electrolyte mix that is sweetened with stevia and tastes fruity. The only food I could bring myself to eat were fruity smoothies that I had delivered from local restaurants. I believe this taste alteration is consistent with a blunted ability to taste sweetness at low concentrations. In the absence of sweetness, bitter tastes go unopposed, and things taste much more bitter to me. Meanwhile, I needed unusually sweet foods for anything to taste normal enough for me to eat it.
At the time, I figured it was the flu. My girlfriend had gotten a flu vaccine and I hadn't, so it would explain why she didn't get very sick. The dry cough was strongly emphasized as a COVID-19 symptom at that time, and I didn't have a cough. I did have a very strange clicking sound when I breathed, but it sounded like it was coming from my throat rather than my lungs, and my breathing sounded clear to my girlfriend when she listened with a stethoscope. So I didn't seem to have a respiratory problem. At that time, it hadn't yet emerged that smell and taste disorders were tell-tale signs. Finally, in the first week of February it just seemed far more likely that I'd have the flu than COVID-19 on the basis that it hadn't yet become apparent that large numbers of people in the US could have COVID-19.
As time has gone on and research has evolved, most of my objections to the idea have fallen apart. I may have been more vulnerable simply from being male. I used my standard cold and flu defense at the time, and while some things may have helped, some of them may have made it worse (I hadn't yet done my research that led me to reject standard cold and flu approaches). I never had the clicking sound properly analyzed by a doctor (it's gone now), and it has become abundantly clear that the majority of COVID-19-positives don't even develop the dry cough, and plenty of people have fever as their main sign. It is also becoming increasingly controversial how far back the virus was in the US, and it is clear by now that most places with major outbreaks had them growing for weeks before they realized there was a problem.
Today's study showing COVID-19 patients are especially likely to have their sensitivity to sweet tastes blunted adds to the data that makes me think I may have had it. I do want to get an antibody test, but I'm weighing the risk of exposure and long lines before I go out and get one.
The Bottom Line
The inability to taste low levels of sweetness is strongly suggestive of COVID-19 and rather common. The inability to taste low or moderate levels of saltiness, or to taste high levels of sweetness, is a very strongly suggestive of COVID-19, but these aren't very common.
Stay safe and healthy,
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* The term “preprint” is often used in these updates. Preprints are studies destined for peer-reviewed journals that have yet to be peer-reviewed. Because COVID-19 is such a rapidly evolving disease and peer-review takes so long, most of the information circulating about the disease comes from preprints.