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Post-Covid brain fog linked to blood clots – UK study

A recent British study has suggested that blood clots in the brain or the lungs might explain some common symptoms of “long Covid”, including brain fog and fatigue, but that further research was needed.

In the study, of 1 837 people who were admitted to hospital because of Covid, researchers said two blood proteins point to clots being one cause, reports BBC News.

It is thought 16% of such patients have trouble thinking, concentrating or remembering for at least six months.

Long Covid can also develop after milder infections.

But the research team, from the universities of Oxford and Leicester, stress:

• Their findings are relevant only to patients admitted to hospital;
• They are “the first piece of the jigsaw” but further research is needed before they can propose or test any potential treatments;
• They tracked cognitive problems at six and 12 months only and through tests and questionnaires, which may “lack sensitivity”.

Study author Professor Paul Harrison, from the University of Oxford, said identifying predictors and possible mechanisms was “a key step” in understanding post-Covid brain fog

But there may still be many different causes of long Covid.

Leicester’s professor of respiratory medicine, Chris Brightling, said: “It’s a combination of someone’s health – before the acute event itself and what happens afterwards – that leads on to physical and mental health consequences.”

The Post-hospitalisation Covid-19 study (PHosp-Covid), in Nature Medicine, blames higher levels of the protein fibrinogen and protein fragment D-dimer for brain fog.

Study author Dr Max Taquet, from Oxford, said: “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.

“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.”

Those with high D-dimer levels also complained of extreme tiredness and being short of breath, and tended to have difficulty holding down a job

A US study found similar results.


PHOSP-Covid study (Open access)


Nature Medicine study – Acute blood biomarker profiles predict cognitive deficits 6 and 12 months after COVID-19 hospitalization (Open access)


BBC article – Brain fog after Covid linked to blood clots – study (Open access)


See more from MedicalBrief archives:


UK analysis confirms risk factors for long Covid


South African research sheds light on microclots’ role in long COVID


Nearly a quarter of hospitalised COVID-19 patients have ‘brain fog’ — Mount Sinai registry


50+ long-term effects of COVID-19 – Systematic review and meta-analysis

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