An unexpected consequence of Covid-19 is emerging: a potential link to long-term brain damage. American researchers studying 227 individuals experiencing neurocognitive issues following a Covid-19 infection discovered a significant increase in levels of tau, an essential protein in the blood plasma. Participants reported symptoms including headaches, dizziness, balance problems, altered taste and smell, and mental confusion. These findings were published in eBioMedicine.
Tau protein is well-known for its association with neurodegenerative diseases. As explained by the Vaincre Alzheimer Foundation, “in Alzheimer’s disease, the tau protein is modified, becoming toxic to neurons and leading to the formation of neurofibrillary tangles.”
A Brain Damage Biomarker
The study suggests that individuals with ongoing neurocognitive symptoms related to Covid-19 may face an increased risk of neurodegenerative diseases. Researchers observed a 59% increase in tau protein (pTau-181) in the plasma of participants after Covid-19 infection, during or following the onset of neurocognitive symptoms, compared to their pre-infection levels.
“The presence of high levels of tau in the blood is a known biomarker of lasting brain damage,” stated Sean Clouston, corresponding author and professor in the Department of Family, Population, and Preventive Medicine at the Renaissance School of Medicine (RSOM) and the Public Health Program at Stony Brook University. He added, “Therefore, these results suggest that long Covid could get worse over time and lead to changes in neurological symptoms or worsening cognitive impairment. However, we do not know whether this increase in tau protein in our sample represents a biological evolution comparable to that observed in people developing Alzheimer’s disease or related diseases.”
Notably, the increase in tau protein levels was more pronounced in individuals experiencing post-acute neurological sequelae of Covid (N-PASC) for over a year and a half. This correlation is concerning, as it could “presage a deterioration of cognitive functions with age.” Further research is needed to determine if elevated plasma tau levels in people with N-PASC correlate with cognitive decline or neurodegenerative diseases.
Sources
Increased levels of Alzheimer’s-linked protein found in some with long COVID, MedicalXpressJanuary 13, 2026
Alzheimer’s disease: the Tau protein is also involved in metabolic disorders, InsermJuly 2017
