Long COVID brain fog may be caused by blood clots, say scientists

LONDON — Answers for patients suffering from long COVID-19 symptoms are finally starting to trickle in, with new research indicating that blood clots may result in longer-term cognitive problems. 

A study published Thursday in Nature Medicine looked at more than 1,800 adults who were hospitalized with COVID-19 and found raised levels of two proteins during their COVID-19 infection — fibrinogen and D-dimer. Both these proteins are involved in blood clotting.

The research also found that presence of these clotting biomarkers during a patient’s hospital stay was linked to ongoing cognitive problems six and 12 months after infection with COVID-19, leading the researchers to believe there may be a causal link between blood clots and long COVID.

”I feel optimistic that the science is beginning to give us real insights into what the causes [of long COVID] are and then the potential treatments,” said Chris Brightling, professor of respiratory medicine at the University of Leicester and one of the authors of the study. “What I’m still disappointed in is … there’s still a lot of patients that are suffering that haven’t yet fully recovered and we don’t know how long it will take for them to recover.”

The results follow other research looking at the effect of the COVID-19 virus on blood clotting, such as a 2022 study indicating that people suffering from long COVID may face an increased risk of abnormal blood clotting. It’s estimated that nearly 36 million people across the World Health Organization’s European region may have experienced long COVID in the first three years of the pandemic.

One participant in the study said that since their illness they “have been plagued by brain fog, concentration-induced fatigue, poor vocabulary, poor memory.” Lead author of the study Max Taquet said it’s people like this that they are doing the research for. “Those are the people that we hope to be able to help down the line by eventually finding a treatment for this condition,” he said.

While the results from today’s study provide a potential explanation for cognitive problems, such as brain fog, sometimes seen in long COVID patients, the researchers stressed that there could be other reasons for these symptoms in hospitalized and non-hospitalized patients. 

Aravinthan Varatharaj, NIHR clinical lecturer in neurology at the University of Southampton, who was not involved in the study, said the findings could point to possible treatments. “Future research should look at whether treatment targeting blood clotting, for example blood thinners, might help people with these symptoms,” he said.