Blood clots may be cause of Long Covid cognitive problems, new study suggests

Scientists are working to understand what causes Long Covid, ITV News' Pablo Taylor reports and meets one man who is still suffering three years later

Blood clots may be the cause of Long Covid cognitive problems, including brain fog, according to a new study.

Researchers found high levels of two proteins during Covid infections in patients who later went on to experience issues with their concentration, memory and thinking.

These proteins - fibrinogen and D-dimer - are involved in blood clotting.

Dr Max Taquet and colleagues from the University of Oxford looked at blood tests from 1,837 people who had been hospitalised with Covid to find potential ‘biomarkers’ associated with subsequent cognitive problems.

Biomarkers are characteristics of the body that can be measured, such as blood pressure.

In a new paper published in Nature Medicine, they identified two separate profiles of biomarkers.

The first was having a high level of a protein called fibrinogen, and the second was a raised level of a protein fragment called D-dimer.

“Both fibrinogen and D-dimer are involved in blood clotting, and so the results support the hypothesis that blood clots are a cause of post-Covid cognitive problems," Dr Taquet explained.

"Fibrinogen may be directly acting on the brain and its blood vessels, whereas D-dimer often reflects blood clots in the lungs and the problems in the brain might be due to lack of oxygen.

"In line with this possibility, people who had high levels of D-dimer were not only at a higher risk of brain fog, but also at a higher risk of respiratory problems."

Dr Taquet continued: “The ultimate goal is to be able to prevent and reverse the cognitive problems seen in some people after Covid-19 infection.

"Although our results are a significant advance in understanding the basis of these symptoms, more research is needed into the causes and effects before we propose and test interventions.”

A participant in the study said: “Since my illness I have been plagued by brain fog, concentration-induced fatigue, poor vocabulary, poor memory. I am unable to process the amount and scale of work that I would previously have done ‘stood on my head’."

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Study supervisor, Professor Paul Harrison, said identifying predictors and possible mechanisms is a key step in understanding post-Covid brain fog.

This study provides some significant clues, he said.

The participants involved in the research were part of a post-hospitalisation Covid study based at the University of Leicester.

Their memory was measured six and 12 months after hospitalisation, using both an objective test and by asking them their own view about their memory.

Dr Rachael Evans, Associate Professor, Department of Respiratory Sciences at the University of Leicester, said: "Large detailed studies such as PHOSP are vital if we're to understand the different ongoing, and often debilitating, symptoms that people are continuing to experience post-Covid."