Blood clots could be the cause of the debilitating brain fogs experienced by people after a Covid infection, Oxford University has suggested.
Around 1.9 million people in Britain say they are still experiencing Long Covid, with around 37 per cent complaining that they have difficulty concentrating.
A new study by Oxford University has found that people who were hospitalised with Covid and went on to have cognitive problems had high levels of two proteins that make the blood clot.
It suggests that excess clotting during a Covid infection may have caused long-term damage that can still be felt more than two years later.
Experts said blood clots could cause a lack of blood supply to the brain or cause fatigue, both of which can cause cognitive problems.
Although the team did not study infected people who were not hospitilised, they said the findings could still apply, and warned that patients in hospital were often treated with anticoagulants, unlike those managing the condition at home.
Dr Max Taquet, a National Institute for Health and Care Research (NIHR) senior research fellow at the University of Oxford, said: “The results support the hypothesis that blood clots are a cause of post-Covid cognitive problems.”
The team looked at blood tests from 1,837 people who had been hospitalised with Covid and also suffered serious and persistent problems with thinking, concentration and memory.
Their memory was assessed at six and 12 months after hospitalisation using both a formal test and by asking them their own subjective view about their memory.
‘Concentration-induced fatigue’ Dr Simon Retford, of the University of Central Lancashire, 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’.”
Tests showed that patients with “brain fog” had high levels of a protein called fibrinogen and raised levels of a protein fragment called D-dimer - both of which are involved in clotting.
Experts believe that fibrinogen may be directly acting on the brain and its blood vessels, whereas D-dimer often reflects blood clots in the lungs, which would mean brain problems are down to a lack of oxygen.
Prof Chris Brightling, NIHR Senior Investigator and Clinical Professor in Respiratory Medicine, at the University of Leicester, said: “One of the things we have been surprised about is the failure of recovery.
“I am disappointed that a number of people are still having persistent problems more than two years on from the pandemic.”
Explaining what might be causing the clotting, Prof Brightling added: “We know that Covid-19 leads to an inflammatory response and activates the lining of the blood vessels and it seems the combination of those is much more profound in Covid-19 than other infections.
“We think this not only leads to the activation of the immune system but also auto-immune activation where the body starts to fight itself.”
‘First piece of the jigsaw’ The team are hoping that in the future doctors will be able to spot which Covid-19 patients are most at risk of long-term problems so that they can be treated early.
Prof Paul Harrison, from the University of Oxford, who supervised the study, said: “Identifying predictors and possible mechanisms is a key step in understanding post-Covid brain fog. This study provides some significant clues.”
“We are not saying it is only the cause of the cognitive problems and there may well be others. This is very much the first piece of the jigsaw. “
The research was published in the journal Nature Medicine.
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