With many people complaining about brain fog, attention problems and confusion after COVID-19, researchers are exploring whether infections could have long-term consequences for the brain.
Early studies are not reassuring.
In several trials made public Thursday, scientists have found changes in brain biology after hospitalization with COVID-19, problems lingering months after infection, and a link between smell loss and mental sharpness in older adults.
Although long-haul COVID-19 is often described as primarily affecting younger people, the new studies suggest that many over 60 also have brain issues long after their initial infections.
Researchers are concerned about the possibility that lingering brain symptoms might lead to dementia years or decades later.
"Is this part of that puzzle of things that may contribute to your (dementia) risk? We don't know yet, but we need to understand that," said Heather Snyder, vice president for medical & scientific relations at the Alzheimer’s Association, an advocacy group.
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Dr. Ronald Petersen, who directs the Mayo Clinic Alzheimer's Disease Research Center in Rochester, Minnesota, said the duration of long-haul COVID-19 symptoms remains unclear.
"It may be months before people get back to square one, but I don't think I would conclude that this is necessarily going to be a permanent, lasting condition," he said.
Petersen, who wasn't involved in the new studies, said it's still early to understand what's going on in the brains of people with long-haul symptoms, such as brain fog and memory loss, but he thinks they're likely due either to lingering inflammation or the after-effects of inflammation that occurred during infection.
Dr. George Vavougios, the lead author of one of the new studies, said he's concerned about the frequency of these brain problems. About half of participants in his study and others are showing cognitive problems after infection, regardless of their age.
He's not sure if the infection could seed future Alzheimer's disease or if the people who are genetically more likely to develop brain problems after COVID-19 are also genetically likely to develop Alzheimer's – or if there won't be any long-lasting effects at all.
"There is no telling of course, because we're at a very early stage, whether this is reversible or a slow burn toward Alzheimer's or other dementias, or this is something that will dissolve over months, weeks, years," he said. "But this is worrying."
COVID-19's 'double whammy' on those with Alzheimer's
People who have Alzheimer's, a degenerative brain condition, have faired poorly during the pandemic, Snyder said, with deaths up 16% last year over previous years, both from COVID-19 infections and perhaps from indirect effects, like social isolation.
Other research has suggested that COVID-19 infection itself may make Alzheimer's worse, said Dr. Reisa Sperling, director of the Center for Alzheimer Research and Treatment at Brigham and Women's Hospital in Boston.
Alzheimer's patients may have both less ability to bounce back after COVID-19 and a direct effect of the virus on the brain. "This looks like a double whammy," she said.
Sperling said she noticed "a pretty substantial decline" in a number of her patients. "Even those whose families worked so hard to take care of them."
Not being able to see grandchildren, get to the gym or social activities took a heavy toll on both patients and their caregivers, she said. People with Alzheimer's and their caregivers should take frequent walks outside, as weather permits, she said, to provide stimulation, social interaction and a bit of a break.
Sperling said she hopes people with Alzheimer's will be eligible for a third booster shot before too long, particularly in light of the highly contagious delta variant.
"I'm very afraid we're going to have a terrible winter for these patients," she said.
Concerns about previously healthy people
The three new studies, presented at the annual Alzheimer's Association International Conference, being held in Denver, each looked at different aspects of the link between COVID-19 and brain issues. None of the studies has yet been peer reviewed, the standard for scientific research, so their findings are preliminary.
One study, from Argentina, included nearly 300 people over 60. Interviewed three to six months after their initial infection, more than half reported lingering problems with forgetfulness and about a quarter still had speech or organizational challenges.
People with continued smell loss were more likely to have these issues, though there was no connection seen between long-term effects and the seriousness of someone's initial infection.
Another study, done by researchers at New York University Langone Health, looked at 310 hospitalized COVID-19 patients over 60 for changes and cell death in their brains. About half had neurological symptoms, particularly confusion.
The patients with symptoms had higher blood levels of markers often associated with brain damage and Alzheimer's.
Sperling said she found the results concerning, because they may suggest "there is a direct effect of COVID-19 on the brain that is potentially accelerating Alzheimer's disease. That of course, is what we all worry about."
But Petersen said these people may not be destined to develop Alzheimer's. Instead, it could be that the markers doctors use to warn of Alzheimer's are more general signs of trouble.
"Rather than jumping to the conclusion that COVID causes Alzheimer's disease," he said, "I think what it tells us or makes us at least think about is 'what are these blood biomarkers really telling us?'"
In his own research, Vavougios, of the University of Thessaly in Greece, looked at 32 people hospitalized with COVID-19 two months earlier. He has since expanded that study to more than 100 people. With a median age of about 50, they were sick enough to require hospitalization, but not sick enough for intensive care, he said.
Before their hospitalization they had been "fully functional and free of other neurological deficits," he said, though most had lost their sense of smell with infection.
Loss of smell might be an "early onset sign of what is to come," he said, and anyone with lingering smell loss or smell distortions after infection should see a neurologist and be followed over time.
The research also suggests that older people shouldn't be so quick to dismiss post-COVID-19 memory loss as a sign of normal aging, Vavougios said.
The Alzheimer's Association supports research collaborations around the world, hoping to speed understanding of any link between COVID-19 and brain problems, Snyder said. "There are still some big questions in terms of cause and effect."
Contact Karen Weintraub at email@example.com.
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This article originally appeared on USA TODAY: Long haul COVID: Scientists study link between dementia, coronavirus