Scientists have identified specific biological changes in taste buds that may explain why some individuals continue to struggle with tasting food more than a year after recovering from COVID-19. The study, published in Chemical Senses, provides the first direct evidence linking persistent taste disturbances to measurable alterations within taste cells.
The research team, led by scientists from the University of Colorado Anschutz and two Swedish universities, examined 28 participants who had experienced taste disturbances for over a year following their infection. None of the participants had been hospitalized for COVID-19. Testing revealed that eight of the 28 participants had clearly abnormal taste scores. Eleven reported difficulty detecting specific flavors, particularly sweet, bitter, and umami, the savory taste associated with foods such as mushrooms and broth. In contrast, their ability to detect salty and sour flavors remained largely unaffected.
Disrupted Molecular Signaling
To understand the cause of this unusual pattern, the researchers collected small tissue samples from the taste buds of 20 participants. The analysis focused on the molecular signals responsible for detecting flavors. The team identified reduced amounts of messenger RNA (mRNA) involved in producing a protein known as PLC2.
This protein plays an essential role in how taste receptor cells communicate with the brain. Specifically, it amplifies the signals generated when the tongue detects sweet, bitter, and umami flavors. Without sufficient levels of the protein, those signals may become too weak to register normally.
“PLC2 acts like a molecular amplifier inside taste cells,” said Thomas Finger, PhD, professor of cell and developmental biology at the University of Colorado Anschutz and corresponding author of the study. “It strengthens the signal before it’s transmitted to the brain. When levels are reduced, the taste signal weakens.”
The discovery also helps explain why some flavors are affected more than others. Cells responsible for detecting salty and sour tastes use different signaling mechanisms that do not depend on PLC2. This difference potentially allows those sensations to remain intact even when other taste signals are disrupted.
Structural Abnormalities in Taste Buds
The abnormalities were not limited to molecular signaling. When the researchers examined taste bud tissue under a microscope, they found that some participants had changes in the physical arrangement of their taste cells.
Finger noted that while some subjects had normal-looking taste buds, others showed structural disorganization. This suggests that both molecular and architectural changes may contribute to persistent taste dysfunction. Together, these findings indicate that lingering taste problems after COVID-19 may involve multiple biological disruptions, affecting both the way taste cells are organized and how effectively they transmit information.
One of the most intriguing aspects of persistent taste loss is how long it can continue despite the body’s natural ability to replace taste cells. Under normal circumstances, cells in the taste buds are renewed approximately every two to four weeks. Yet the researchers found signs that the molecular processes needed for normal taste signaling may remain disrupted for much longer in some people.
Most individuals who experience taste changes during COVID-19 regain their normal sense of taste within weeks or months. However, a small group continues to experience symptoms long after the infection has resolved. The new findings provide measurable biological evidence that could help explain why recovery takes so much longer for these patients.
“Our findings offer measurable evidence of long-term taste disruption in some post-COVID patients long after the virus has been cleared,” the authors write. Although the discovery sheds light on a previously unexplained symptom, important questions remain. Scientists still need to determine whether these molecular abnormalities can eventually return to normal and whether treatments designed to restore healthy taste signaling could help people recover their sense of taste.
Source: ScienceDaily
