Three years into the global COVID-19 pandemic, scientists are still learning more about how the virus impacts the body. Now, there’s a new finding: COVID-19 is linked to brain damage.
That’s the major takeaway from a new study published in the journal Nature. For the study, researchers analyzed data from 401 patients aged 51 to 81 who underwent brain scans before they contracted COVID-19 and months after they were infected. Their scans, which were conducted about three years apart, were compared to those of 384 people who weren’t infected with COVID-19, but had similar characteristics like age, sex, medical history, and socioeconomic status to those who did contract the virus.
The researchers noted that it’s normal to lose some gray matter each year, which helps control movement, memory, and emotions. But patients who had COVID-19—who had a second brain scan about 4.5 months after they were infected—had more gray matter loss than those who didn’t have the virus, losing between 0.2 and 2% extra gray matter in different brain regions between their two scans. They also lost more brain volume and showed more tissue damage in certain areas, including those linked to the sense of smell, than those who never had the virus.
Most of the study participants were never hospitalized with COVID-19 (only 15 of them were), and the researchers noted that the trend in brain changes was still seen when the hospitalized patients were excluded from the findings.
Whether you’ve had COVID-19, love someone who has had the virus, or are just curious, it’s understandable to have questions about what’s going on. Here’s what you need to know.
Why might COVID-19 cause brain damage?
It’s not entirely clear, but the researchers said in an FAQ they shared online that it seems to linked to loss of smell. “It is known that areas of the brain that are not being used can atrophy, so it will be important to understand how much of this may be related to loss of smell,” says infectious disease expert Amesh A. Adalja, M.D., a senior scholar at the Johns Hopkins Center for Health Security, who did not work on the study.
“Another explanation could be the effect of the virus itself, either because it invades the brain, or because it causes inflammation or immune reactions,” the researchers wrote. However, they added, “it is still unclear why such invasion or inflammatory/immune reactions should be mainly seen in specific regions of the brain, but not others.”
What kind of symptoms can people experience from this?
The researchers didn’t explore this. However, they did have study participants take cognitive tests around attention and efficiency in doing something complex. That showed that, on average, there was “larger cognitive decline” in people who were infected than those who were not infected, the researchers wrote.
“When you have inflammation in the brain from whatever cause, it can cause symptoms,” says Santosh Kesari, M.D., Ph.D., neurologist at Providence Saint John’s Health Center in Santa Monica, Calif., and regional medical director for the Research Clinical Institute of Providence Southern California. But Dr. Kesari says it’s “unusual” to see changes in brain matter volume after having a virus. That, he says, “means there's a pretty severe inflammation going on.”
The actual symptoms depend on the area of the brain that’s impacted, he says. But, given that this seems to be tied to areas of the brain that are linked to smell and taste, Dr. Kesari says it makes sense that the loss or change of these senses would be symptoms.
Amit Sachdev, M.D., M.S., medical director in the Department of Neurology at Michigan State University, agrees and says that this can have big implications for people. “Smell is important for taste and for threat recognition,” he says. “Without smell, food can be very bland. Also, some safety measures that use smell to alert for a problem won’t work. The most commonly cited example is being able to smell the ‘rotten egg’ smell added to natural gas. If you can't smell, you might not be able to detect a natural gas leak.”
Can COVID cause other neurological disorders?
This is still being explored. However, Dr. Adalja points out that COVID-19 has been linked to a few other neurological health conditions, including:
- New loss of taste and smell
- Peripheral neuropathy (weakness, numbness, and pain from nerve damage)
- Guillain-Barre Syndrome (an autoimmune disorder where a person's immune system damages the nerves, leading to muscle weakness and sometimes paralysis)
- Encephalitis (inflammation of the brain that can be caused by a virus or bacteria)
Fatigue and body tingling can also happen as a result of COVID-19, Dr. Sachdev says, adding, “we have seen many patients with these long-term complications.”
How long does COVID-19 affect the brain?
That’s also unclear. The researchers noted that they have no clue how long these brain changes will last. “Whether this deleterious impact can be partially reversed, or whether these effects will persist in the long term, remains to be investigated with additional follow up,” they wrote.
But it’s possible that people can regain at least some of their brain health over time. “Once damaged, the brain can recover but the recovery tends to be incomplete,” Dr. Sachdev says. “Brain injury is permanent. The area that is damaged can't regrow." Still, he says, “brain plasticity allows for some recovery.” Dr. Sachdev says that it’s possible that people can regain their sense of smell afterward “but that smell might not be the same as before the infection.”
If you’re still having unusual symptoms after having COVID-19, Dr. Kesari recommends seeing your doctor for an evaluation. But, he points out, doctors are still learning more about the after-effects of having COVID-19. “There is further work that needs to be done,” he says. “There may be additional treatments to help the brain recover better, but we need more research.”
This article is accurate as of press time. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus develops, some of the information may have changed since it was last updated. While we aim to keep all of our stories up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news. Always talk to your doctor for professional medical advice.