How much are covid-19 and Alzheimer's disease alike?

As of this week, about 5.9 million people have died from covid-19 world-wide with more than 400 million confirmed cases.  The most common immediate causes of death are related to the respiratory system via covid pneumonia and damage to the heart.  But this is a complex infection, and it affects many organs of the body -- including the brain.  According to this recent study published in the journal Alzheimer's and Dementia, its attack on the brain is sometimes very similar to that of Alzheimer's disease.

You have almost certainly heard that loss of smell is a symptom of covid.  Well, according to the study, loss of smell is also sometimes seen in early stages of Alzheimer's disease and is evidence of neurological damage.  Headaches are also a symptom.  And what is a headache other than evidence of inflammation in the brain?  As we explained in Beating the Dementia Monster, inflammation in the brain is a key part of the process by which Alzheimer's disease evolves.  And you have likely heard that people with covid report "brain fog."

The researchers who performed the study reviewed the available literature on the disease.  In their own laboratory, they also examined brain tissue from people who had died from covid as well as brain tissue from a control population.  The upshot is that they found evidence of both oxidative stress and inflammation in covid patients similar to that of Alzheimer's disease patients.  While they don't say that they found the tau tangles which are markers of Alzheimer's disease, they did find the mechanisms that lead to tau tangles appeared to be in motion.  (They did not, however, find beta amyloid plaques or evidence that beta amyloid was even forming.) 

So what do we make of this?  It seems likely that people with Alzheimer's disease are at risk of having their condition aggravated by covid, perhaps significantly.  And since Alzheimer's disease likely begins 15 years before the first symptoms, there are a lot of undiagnosed people out there who are getting covid.

The authors believed that the primary contribution is to have found a link between the brain's inflammatory response to covid and the way the tau protein degenerates in Alzheimer's disease.  They are hoping this will lead to treatments for damage to the brain caused by covid.