Can a Coronavirus Infection Lead to Dementia?

The investigators found that the patients who had neurological symptoms — the most common was confusion caused by a condition that can result from an infection — also had higher levels of so-called biomarkers in their blood that indicate brain injury, neuroinflammation and Alzheimer's disease, the most common form of dementia. In fact, these markers were “markedly elevated,” according to researcher Thomas Wisniewski, M.D.

"So this suggests that perhaps having a COVID infection with these sorts of complications is somewhat similar to undergoing a [traumatic brain injury] and may predispose someone to a higher risk of Alzheimer's disease and related problems,” said Wisniewski, a professor of neurology, pathology and psychiatry at New York University Grossman School of Medicine.

More research is needed to understand what these elevated biomarkers mean for cognition in the long run, and whether an uptick in Alzheimer's cases could become a consequence of the pandemic. More than 6 million Americans currently live with the disease; that number is already projected to more than double by 2050.

"We just have to follow these folks over the next few years to really address that issue,” Wisniewski said. But for now the research “speaks to the potential for a very big problem,” he added. So far, more than 2.3 million Americans have been hospitalized with COVID-19.

Loss of smell linked to memory, behavior changes

Experts have also linked loss of smell, a common symptom of COVID-19, to cognitive impairment in people who had coronavirus infections.

Neurologist Gabriel de Erausquin, along with colleagues from an Alzheimer's Association–led coronavirus consortium, followed a few hundred older adult Amerindians in Argentina who had COVID-19. More than half of the population had frequent problems with forgetfulness in the three to six months that followed their bout with COVID-19; about 25 percent experienced other cognitive issues, including problems with language and behavior control. And all of these symptoms were associated with persistent loss of smell, not severity of the initial illness.

In fact, very few people in the population studied were hospitalized for COVID-19, de Erausquin said; most had mild symptoms or no symptoms at all. Yet the lingering neurological effects that many of the older adults experienced were “broad enough and severe enough that in any other context, you would consider that dementia,” said de Erausquin, a professor of neurology of the University of Texas San Antonio Long School of Medicine, whose research was highlighted at the Alzheimer's conference.

One possible explanation: COVID-19 “triggers the Alzheimer's process” in people who are more at risk for developing the disease, he suggested. Loss of smell has been associated with a number of brain disorders, including Alzheimer's and Parkinson's disease. “And we also know that the structures within the brain that subserve olfactory [smell] function overlap significantly with those that are affected by Alzheimer's disease early on in the process of illness,” de Erausquin added.

It may also be that the lingering neurological effects seen after COVID-19 are “a completely separate disease that looks like Alzheimer's,” he said. “We just don't know enough about the process or the course of illness to answer those questions.”

De Erausquin and his colleagues plan to continue their research in hopes of finding these answers and to better understand whether COVID-19-related cognitive problems are more likely to persist or get better with time.

In the meantime, his advice for anyone who experiences brain changes after COVID-19 is to talk to a health care professional. “Because there are preventive measures that we know work very well in reducing the risk of progression of Alzheimer's, such as regular physical exercise, keeping a healthy Mediterranean diet, keeping social and intellectual engagement — those things reduce, by as much as 40 percent, the risk of progression to dementia,” he said.

"But also, and this is crucial, we just don't know if they are the same process. At this point, we cannot say that people who have [lingering symptoms] after being exposed to the virus will go on to have progressive cognitive decline. And that is a crucial question that we need to answer.”

COVID takes toll on brain health of older adults

It's unclear how, exactly, COVID-19 can cause or exacerbate neurological issues. Inflammation triggered by the infection could be to blame. Many COVID-19 patients also experience clotting abnormalities, which could lead to “small strokes or small ischemic injury,” Wisniewski said. Another theory is that the virus invades the brain directly.

So far, more than 34 million Americans have tested positive for COVID-19, data from Johns Hopkins shows. And with global coronavirus cases topping 196 million, Snyder, with the Alzheimer's Association, says, “it is imperative that we continue to study what this virus is doing to our body and brain.”

Adults already living with dementia have also been affected by COVID-19. A government report found that Medicare beneficiaries with dementia were more likely to contract COVID-19 and die from the disease than the general Medicare population. What's more, deaths from Alzheimer's disease were about 16 percent higher in 2020 than in previous years, a report from the Alzheimer's Association shows. Most of the excess deaths can be attributed to COVID-19.

Rachel Nania writes about health care and health policy for AARP. Previously she was a reporter and editor for WTOP Radio in Washington, D.C. A recipient of a Gracie Award and a regional Edward R. Murrow Award, she also participated in a dementia fellowship with the National Press Foundation.