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(CNN) -
Covid-19 may be linked to cognitive decline and the acceleration of Alzheimer's-like symptoms, researchers reported Thursday.
Researchers from an international consortium seeking to understand the long-term consequences of COVID-19 on the central nervous system have found memory problems and biological markers similar to those seen in Alzheimer's disease patients.
Both diseases are characterized by inflammation of the brain.
Dr. Gabriel de Erausquin, a professor of neurology at the University of Texas Health Sciences Center, and his colleagues studied more than 200 adults aged 60 and over from Argentina who had been infected with COVID-19.
As explained at the International Conference of the Alzheimer's Association, those with a persistent loss of smell were more likely to experience cognitive problems.
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Between three and six months after being infected, more than half of the patients continued to have forgetfulness problems and about a quarter experienced additional cognitive problems.
The degree of illness of a patient with Covid-19 was not an indicator of whether he would experience cognitive decline.
"The severity of the initial illness does not predict who is going to get this," Erausquin told CNN.
"In fact, many of them had minimal symptoms: just a cold or loss of smell."
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Cognitive problems, including persistent forgetfulness, difficulty in sequencing tasks, and forgetting words and phrases, are similar to those seen in Alzheimer's patients.
Erausquin pointed out that the parts of the brain responsible for the sense of smell coincide with those affected by Alzheimer's disease.
He also noted that the cognitive symptoms observed by his team appear to be different from "brain fog" or cognitive dysfunction, associated with the long-term symptoms of COVID-19, which is sometimes seen in younger patients.
"Brain fog in younger individuals tastes different, so to speak," Erausquin said.
"They have more attention problems, more problems concentrating, and they often have more anxiety and depression."
It is too early to know if cognitive problems will worsen over time, as they would in Alzheimer's patients, or if these patients will recover, Erausquin said.
Biological markers related to Alzheimer's
In additional research presented at the conference, Dr. Thomas Wisniewski, a professor of neurology at New York University Grossman School of Medicine, and his colleagues found that COVID-19 patients older than 60 years had biomarkers in blood that is also found in Alzheimer's patients.
Among the 310 COVID-19 patients admitted to New York University Langone Hospital, the team found that those with neurological symptoms had higher levels of Alzheimer's-related biomarkers.
Those biomarkers include a protein called tau that has been linked to Alzheimer's and other compounds known as neurofilament light, an indicator of nerve cell damage, among others.
"These findings suggest that patients who had COVID-19 may have an acceleration of Alzheimer's-related symptoms and pathology," Wisniewski said in a statement.
They warn that patients recovered from covid-19 suffer from "cognitive deficit"
Wisniewski commented that more research is needed to understand how those biomarkers affect long-term cognition in people who became ill from COVID-19.
"That's the kind of thing that makes you suspect that there may indeed be an overlap with Alzheimer's disease, of some sort," explained Erausquin.
"But it is too early for that. We need a lot more data."
Researchers have long been attentive to possible links between respiratory diseases and the brain, Heather Snyder, vice president of medical and scientific relations at the Alzheimer's Association, told CNN.
Snyder noted that similar changes in cognition and behavior, such as increased anxiety and sleep disturbances, were seen in people infected during the 2003-2004 outbreaks of Severe Acute Respiratory Syndrome, or SARS, and Middle East Respiratory Syndrome. or MERS.
Long-term questions
Snyder said researchers are working hard to understand the long-term consequences of these findings on COVID-19 and cognition.
"We also have to try to really understand the impact on the brain, in general, because we know that when our brains can be vulnerable for other reasons, it can also increase our risk of Alzheimer's," Snyder said.
Erausquin stressed that the research does not show that COVID-19 increases a person's risk of suffering from Alzheimer's and that there are big questions that can only be answered with time.
"I'm trying to understand if the virus accelerates a pre-existing condition, or if it causes a new Alzheimer's-like process to start and then progress, or if it behaves like a fixed problem that will make a full recovery," he said.
"We don't know that yet."
What researchers do know is that older adults can take steps to lower their overall risk of cognitive decline, such as being physically active, staying socially connected, and eating a healthy diet.
"I think it's important to remember that regardless of the reason for cognitive decline, the brain is plastic, and many of these interventions likely reduce the risk of impairment or the risk of progression," Erausquin said.
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