Researchers led by Prof Matthew Campbell at Trinity College Dublin have uncovered a likely link between brain fog in long Covid patients and a leaky blood-brain barrier. This could be due to the neurological symptoms associated with the lingering effects of the virus. The findings, published in the journal Nature Neuroscience, could pave the way for new treatment approaches.

Long Covid, characterised by persistent symptoms beyond the acute phase of the illness, often includes cognitive impairments such as forgetfulness and difficulties concentrating, collectively referred to as brain fog. The blood-brain barrier, responsible for regulating the balance of substances between the blood and the brain, has emerged as a crucial factor in understanding these cognitive issues.

The study involved the analysis of serum and plasma samples from 76 hospitalised Covid patients in 2020 and 25 individuals before the pandemic. Samples from 14 Covid patients with self-reported brain fog showed elevated levels of the protein S100β, indicating a potential breakdown of the blood-brain barrier.

A subsequent MRI study involving recovered and long Covid patients revealed that those experiencing brain fog exhibited signs of a leaky blood-brain barrier. The study suggests that a tighter blood-brain barrier in some individuals may offer protection against brain fog in long Covid, explaining why the symptom doesn’t manifest universally.

Further investigation revealed increased levels of clotting-related proteins in long Covid patients with brain fog, hinting at a connection between blood-brain barrier integrity and disruptions in clotting proteins. This association raises the possibility of new avenues for treating neurological conditions, including brain fog.

Prof Paul Harrison from the University of Oxford previously suggested blood clots in the brain as a possible cause of brain fog in long Covid. His latest suggestion is that the study supports the idea that abnormalities in the lining of blood vessels in the brain are present in individuals with post-Covid brain fog.

Harrison also acknowledged the study’s limitations, emphasising that the results are based on patients from the first wave of Covid. The applicability of the exact mechanisms to individuals with later virus variants or those who have been vaccinated remains uncertain.

Prof Claire Steves of King’s College London raised concerns about the small number of participants in the study and the challenge of unclear and self-reported definitions of brain fog.