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The effect of Covid on the brain
I won’t go into how Covid has affected the NHS and caused incredible emotional strain and loneliness because I’m sure you’re already very aware of all that, and to be honest, it makes me a bit sad. But despite the well documented effect of covid on society and on the body, we still have a way to go to understand the effect of covid on the brain.
We read about the link between losing the sense of smell (termed “anosmia”) and neurodegeneration in conditions like Alzheimer’s and Parkinson’s disease, and we know covid can sometimes cause long term effects on the sense of smell. We’ve also seen an interesting link between covid and neurological symptoms like depression, memory loss and cognitive fatigue, but how does this all tie together?
In the upper part of the throat behind the nose lies the nasopharynx. This area is important in mediating sense of smell and the cells here have a protein on their membrane called Angiotensin‐converting enzyme‐2 (ACE2). When we breathe in the covid virus, it binds to ACE2 receptors in the nasopharynx and enters the cells. Some cells in the lung, nasal passages and intestines also have this protein on their membranes, so these are the cells that suffer the most from Covid infection. Researchers have suggested that as the nasopharynx is so closely connected to the nerve that transmits information to the brain about smell, this might be the route coronavirus takes to reach the brain. We still don’t completely understand how Covid affects the brain, but it appears that the virus directly attacks some brain cells, alters blood flow to some regions, and triggers an immune response that is harmful to brain cells.
Scientists have noticed a link between Alzheimer’s and a higher risk of more severe Covid infection in some individuals – this is thought to be due to a specific version the apolipoprotein E (APOE) gene called APOEε4. APOEε4 is associated with a higher chance of developing late onset Alzheimer’s disease, and with difficulties in recognising and discriminating between smells. Recent studies show that people with APOEε4 have a greater risk of getting severe Covid and post-Covid mental fatigue. If Covid infection causes anosmia, and anosmia correlates with an increased risk of developing Alzheimer's disease, then it is possible that people with this particular version of the APOE gene might be more likely to develop Alzheimer’s disease, or for disease progression to increase, following Covid infection.
That seems a bit worrying. What can we do about this? We need to look after the residents in our care homes and vulnerable members of our families. Easier said than done I know, especially while trying to balance the need to isolate to keep everyone safe and the need for social interaction and human contact. We also need to knuckle down to more research into the long term effects of Covid and explore therapies that focus on treating the mental effects of the disease. Look after yourselves.
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