United States: A vast majority of people who experience long Covid have trouble with memory as well as difficulties focusing. “Brain fog” is what they call this.

However, the latest research shows that the symptom is linked to the damaged blood-brain barrier.

The barrier serves as a gatekeeper for which substances or materials can get in or out of the brain.

Prof Matthew Campbell, co-author of the research at Trinity College Dublin, said, “It’s all about regulating a balance of material in blood compared to the brain,” as reported by the Guardian.

Campbell added, “If that is off balance, then it can drive changes in neural function, and if this happens in brain regions that allow for memory consolidation/storage, then it can wreak havoc.”

The findings report is published in the journal Nature Neuroscience, in which Campbell and his team reported how they studied serum and plasma samples of 76 patients who were hospitalized because of Covid in March or April 2020 and the samples of 25 people who came before the pandemic.

The findings of the study

Besides, among other findings, the team found that the samples from 14 Covid patients who reported brain fog had higher levels of S100β protein than the samples from Covid patients who did not have brain fog and who did not have Covid.

This protein is synthesized by cells in the brain and is not found in the blood in normal physiology. Thus, it seems like the blood-brain barrier is broken down in these patients.

How did the study take place?

The researchers then went ahead and enrolled ten people who had recovered from COVID-19 and 22 people with long COVID-19, 11 of whom reported brain fog.

As no one had, at that time, received a Covid vaccine or been admitted to hospital for Covid, the phenomenon was labeled as ‘Long Covid,’ the Guardian reported.

The patients were given an MRI scan in which a drug was injected through the vein.

Results of the study

The results indicate that long Covid patients experiencing brain fog did show a leaky blood-brain barrier, while long Covid patients without this symptom or who had recovered did not show the same.

Campbell further stated that it was possible that individuals with a more powerful blood-brain barrier may be better safeguarded from the brain fog should they have long COVID, meaning that the symptom does not appear in all cases.

Therefore, analysis of a subgroup of patients with headaches revealed that long Covid patients with brain fog also had an increased level of proteins linked to clotting.

Campbell said the result did not surprise him because the disruption of proteins responsible for clotting could lead to disruption of cells that line blood vessels.

He added, “The whole concept that a lot of these neurological conditions, including brain fog, could be treated by simply regulating the integrity of the blood-brain barrier is really exciting,” as the Guardian reported.

The research is for long-Covid patients, but Campbell remarked that the findings could relate to people with brain fog caused by conditions similar to ME, even if further work is essential to confirm that.

University of Oxford’s Prof Paul Harrison, one of the authors of earlier research highlighting blood clots in the brain as a possible cause for brain fog in people with long Covid, stated that the new study is an important one.

He further added, “It shows that abnormalities in the lining of blood vessels in the brain occur in people with post-Covid brain fog, and adds to the evidence that abnormal blood clotting also contributes.”

However, he noted that the findings came from patients who only had COVID-19 in the first wave, so it was possible that the same mechanisms could have occurred in others, such as those who were presented with later variants of the virus or were vaccinated.

Harrison added, “Likely, a range of processes explain brain fog and other features of post-Covid syndrome.”

Bigger and more research for better outcome

Prof Claire Steves of King’s College London noted that the small number of participants meant that the observed differences between groups were often statistically significant and could be erroneously attributed to chance, while in this case, brain fog was not clearly defined and self-reported by the participants.

She said, “Therefore, it is difficult to be sure how applicable these results are to the millions of people who have experienced this phenomenon,” as the Guardian reported.


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