COVID-19 Can Leave a Lasting Mark on the Brain—Especially for Older People

July 19, 2024 5:13 PM EDT

COVID-19 no longer poses the urgent public-health threat it once did. But recent research points to a good reason to keep the virus in mind: it could leave a lasting stamp on yours.

Studies suggest that COVID-19 is associated with possibly long-lasting changes to the brain, potentially contributing to cognitive problems like brain fog, mental fatigue, and memory loss, as well as neurological and mental-health issues. The virus seems able to damage blood vessels and support cells in the brain and may kickstart changes to the immune system that also affect brain function, says Dr. Wes Ely, co-director of the Center for Critical Illness, Brain Dysfunction, and Survivorship at Vanderbilt University Medical Center.

What does that mean for the average person as the virus once again circulates widely?

Many people of all ages recover just fine, mentally and physically, after a COVID-19 case. But lingering cognitive effects are a real risk, particularly for older people, Ely says. Older adults are more likely to experience severe COVID-19, which has long been linked to a higher risk of long-term complications. And they may have had preexisting cognitive issues that become worse after infection.

“They don’t have as far to fall before they experience a clinical awareness that they’re having problems,” Ely says. Research has shown that a COVID-19 case can accelerate mental decline in older adults with dementia.

The virus may also raise the chances of developing dementia for the first time, suggests a research review of 11 previous studies that was posted online in February before being peer-reviewed. Adults older than 60 who survived COVID-19 had a significantly higher risk of developing dementia a year later, compared to similar-aged people who hadn't had a respiratory infection. Cognitive impairment was almost twice as likely among people who'd had COVID-19 compared to an uninfected control group.

Dan Shan, co-author of the study and a former junior researcher at Columbia University, wrote in an email that more research is required to confirm whether the virus is directly causing dementia, but his team is "pretty confident" there's a connection.

This link may not be unique to the virus that causes COVID-19. "Numerous studies have shown that respiratory infections like the flu can lead to greater risks of cognitive deficits or dementia," Shan wrote. "However, these findings haven't captured public attention as much as COVID-19."

Age may be an important risk factor for cognitive issues, but younger people shouldn’t feel immune from COVID-19’s effects, either. Ely says there are “people in their 30s and 40s [who] have neurocognitive deficits that look like mild dementia.”

A large study published in the New England Journal of Medicine in February backs up that warning. It suggests that COVID-19 can hinder cognitive performance among adults of all ages, even those who ostensibly recover fully.

In that study, more than 100,000 adults in the U.K. took tests meant to measure cognitive skills. When the researchers compared people who’d had COVID-19 with demographically similar people who’d never had a confirmed case, they found that the COVID-19 survivors, on average, performed worse “across the board, but particularly on measures of memory function, executive function—for example your ability to decision-make and plan—and reasoning,” says study co-author Adam Hampshire, a professor of cognitive and computational neuroscience at King’s College London.

The study didn’t measure differences in individual participants' performance pre- and post-COVID, and the results don’t necessarily mean that every single person who catches COVID-19 will experience cognitive decline, Hampshire says. But, when looking at the study group as a whole, there were clear differences between those who’d had COVID-19 and those who hadn’t. The results equated to about a three-IQ-point deficit among people who recovered completely from COVID-19 versus those who'd never had it. Among people with unresolved Long COVID symptoms and those who’d been admitted to the ICU, the deficits jumped to six and nine IQ points, respectively.

But there are some reasons for optimism. In the study, cognitive differences were not as pronounced among people who’d gotten vaccinated multiple times, nor those who got COVID-19 later in the pandemic—which suggests risks may be lower now than they were in 2020.

The researchers also didn’t find a dramatic difference between people who’d been infected once versus multiple times. (Other studies, however, have found that repeat infections carry compounding risks of brain complications, as well as other serious health problems.) And people who had Long COVID symptoms but eventually got better “performed at the same [cognitive] level as people who had shorter-duration symptoms,” which suggests some effects of Long COVID may be reversible, Hampshire says.

The data on COVID-19 and cognition are worrying, but more research is required to fully assess the virus' long-term effects. "These relationships need to be observed over a longer period, potentially 5-10 years, to fully understand the impact of COVID-19 on the development of new-onset dementia, a condition that progresses slowly," Shan wrote.

Research on if and how COVID-related brain damage can be reversed is ongoing and provides reason for hope, Ely says. But for now, the cognitive risks of COVID-19 are yet another reason to stay up-to-date on vaccines and avoid infection if at all possible.

More Must-Reads from TIME