Will COVID Brain Fog Increase Risks for Alzheimer’s Disease?

Brain fog is a common symptom of COVID–both during acute sickness and for people with long COVID. Because of these cognitive symptoms, I worry that COVID-19 may increase the risk of Alzheimer’s disease and other forms of dementia.

For the last year, I have suggested to my students that we may see an increase in Alzheimer’s rates in ten years. I was too optimistic. There’s new evidence for an increased risk of Alzheimer’s disease appearing within one year of people having been sick with COVID-19.

COVID and Brain Fog

COVID-19 makes some people feel like they are in a mental fog. When sick, people frequently report this cognitive symptom. They can’t think well, forget things, can’t process information, and experience difficulties with tasks that once seemed easy. For most people, this brain fog dissipates as they start to recover.

For people with long COVID, however, cognitive symptoms are often a critical aspect of the problems. In a recent article, Ed Yong provided a disturbing and sad picture of what many people with long COVID experience. For many, their cognitive problems are severe enough that they experience challenges doing many activities they have done for years. Some have been unable to return to their previous jobs because they can no longer perform the same cognitive tasks.

Last year, when first writing about COVID brain fog, I described a longitudinal study of the cognitive effects of COVID-19. Hampshire and colleagues (2021) had cognitive performance information on a large sample as part of an ongoing study. In a follow-up set of measures, they found that people who had COVID during the first year of the pandemic showed long-term cognitive declines. These declines were large enough to compare to a seven-point IQ drop.

And I will simply note that we have a good friend who now has chronic fatigue syndrome, for which COVID was a contributing factor. Our friend can no longer do many of the challenging cognitive tasks she used to do easily. Like the people that Ed Yong described, she also can have serious exhaustion and other physical symptoms following even modest cognitive exertion–such as having emotional conversations or a conversation with additional noise in the background.

COVID and Alzheimer’s Disease Risk

But these long COVID symptoms, while troubling, do not mean an increased risk of Alzheimer’s disease. The cause of Alzheimer’s disease has always been poorly understood. But viral infections have been considered one possible cause of many long-term brain and cognitive declines. For example, findings earlier this year provided evidence for a link between multiple sclerosis and the Epstein-Barr virus.

Now the bad news. In a new analysis concerning the onset of Alzheimer’s disease, Wang and colleagues (2022) found a link to COVID. They looked at the medical records of a large sample. They checked which people had COVID during the previous year. They also had information on the individuals diagnosed with Alzheimer’s post-COVID. They found an increased risk of Alzheimer’s onset in the year following COVID among people older than 65. The elevated risk was fairly substantial–nearly a two-thirds increase in new Alzheimer’s diagnoses. In one year, this is a dramatic increase in risk.

The relative risk increased, but the actual risk remained relatively low. The odds of people being diagnosed with Alzheimer’s in a single year, even with an elderly sample, generally remained low. That is why I thought it would be a decade before we saw any possible effects of COVID on Alzheimer’s rates. But the evidence is already starting to appear.

This new evidence may increase investigations of what types of viruses have contributed to long-term cognitive declines. Historically, COVID has not been the cause of Alzheimer’s disease. But other viruses have possibly contributed to Alzheimer’s onset.

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The risks of long COVID are reason enough to avoid catching the disease. But the added risks of cognitive impacts–when sick, during long-COVID, or later in life–add reasons to avoid COVID.

People sometimes catch COVID multiple times, and we do not know the possible risks of repeated infections. Get vaccinated and use a mask in crowded spaces until the infection rates drop. Even if you are not worried about the immediate health consequences, we should all be careful of these long-term risks.