Persistent taste dysfunction after COVID 19 linked to cellular abnormalities

Scientists have identified molecular and structural changes in taste buds that may explain why a small subset of people experience long-term taste loss after COVID-19 infection.

The study, published last month in Chemical Senses, provides the first direct evidence linking patients' reported taste changes to measurable biological abnormalities inside taste cells.

What causes long-term taste loss after COVID-19?

Researchers from the University of Colorado Anschutz and two Swedish universities studied 28 non-hospitalized patients who reported persistent taste disturbances more than one year after contracting COVID-19.

Key findings:

• 8 of 28 patients showed clearly abnormal taste test scores
• 11 patients reported specific loss of sweet, bitter and umami taste
• Salty and sour taste were largely preserved

To understand why, researchers performed biopsies on taste buds from 20 participants.

Molecular defect identified in taste receptor cells

The team, organized by Göran Hellekant, PhD, of the University of Wisconsin and the Swedish University Of Agricultural Sciences, discovered reduced levels of messenger RNA (mRNA) responsible for producing a protein called PLCβ2 - a critical signal amplifier in receptor cells that detect sweet, bitter and umami tastes.

PLCβ2 acts like a molecular amplifier inside taste cells. It strengthens the signal before it's transmitted to the brain. When levels are reduced, the taste signal weakens."

Thomas Finger, PhD, professor of cell and developmental biology, University of Colorado Anschutz and corresponding author of the study

Importantly, taste cells that detect salty and sour flavors do not rely on this protein, which may explain why those tastes are less affected.

Structural changes also observed

In addition to molecular abnormalities, some patients showed altered taste bud organization under microscopic examination.

"Some subjects had normal-looking taste buds, while others showed structural disorganization," Finger said. "This suggests that both molecular and architectural changes may contribute to persistent taste dysfunction."

Why does taste loss persist?

Taste bud cells are normally replaced every two to four weeks. But the researchers found evidence that cellular signaling disruptions may persist far longer in certain individuals.

While most COVID-19 patients recover their sense of taste within weeks or months, this study provides quantitative biological evidence explaining why recovery may be prolonged in a small group.

"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.

Further research is needed to determine whether the molecular dysfunction can fully reverse and whether targeted therapies might restore normal taste signaling.