Study suggests COVID-19 harms parts of the brain, even in mild cases

The ambulance bay at St. Luke's Hospital in New Bedford in January.Jonathan Wiggs/Globe Staff

Since the start of the coronavirus pandemic, one of the stranger symptoms of COVID-19 has been a loss of smell, taste, or both. Now, a study of brain scans of people who have had the disease offers new clues in the mystery.

Researchers from Oxford University said they had found that people who had COVID-19 had a “loss of grey matter” in areas of the brain related to smell and taste.

A review of hundreds of brain scans revealed “a significant, deleterious impact of COVID-19 on the olfactory and gustatory cortical systems,” the study said.

The research team also included members from Imperial College in London and from the US National Institutes of Health. The observational study is out in preprint form; it has not yet been peer-reviewed. The lead author declined to comment since the study hasn’t been published yet.

The researchers scrutinized before-and-after brain scans collected on average three years apart from 782 people as part of the UK Biobank project. The study group included 394 people who had gotten COVID-19 by the time of their second scan and 388 people who hadn’t. The researchers said among those study participants who had gotten sick, a high number had mild cases.

“It’s very concerning because it does suggest that the virus could be having a direct effect on certain portions of the brain,” Dr. Scott Gottlieb, the former head of the Food and Drug Administration, said on CBS’ “Face the Nation.”

“I think what it suggests is that the balance of the information that we’re accruing does indicate that COVID is a disease that could create persistent symptoms,” he said. “So, this isn’t a benign disease. This is something you want to avoid. And the bottom line is, we have the tools to avoid it through vaccination.”

Dr. Ashish Jha, dean of the Brown University School of Public Health, said in a series of tweets last week that it was an “important study.”

He said it appeared to provide “good evidence that infections lead to neurologic damage in some portion of people.”

The findings highlighted the need to put effort into addressing the long-term impacts of the disease, and the fact that “we should not have been cavalier” about a disease whose full effects are still unknown, he said.

Dr. Eric Holbrook, chief of the rhinology division at Mass Eye and Ear and an associate professor of otolaryngology at Harvard Medical School, was more cautious in his assessment of the study.

He noted the paper had not been peer-reviewed yet. “You really have to be careful with statements being made by these papers because they haven’t been vetted,” Holbrook said.

Researchers suggested their findings might support a “popular theory” that the coronavirus enters the central nervous system through the nose. But Holbrook noted there were other possible explanations, including that the coronavirus disabled nerves in the nose, and the brain areas changed because of a lack of stimulus from those nerves.

He also said the researchers should have inquired whether the study participants had experienced loss of smell, taste, or both, which would have allowed them to compare symptoms with the changes found on the brain scans.

People who lose their sense of smell and taste fall into two groups, he said. One group recovers in two to three weeks, while the other group experiences a more prolonged loss. A large number of the latter get function back, but it’s a slow process, he said.

It’s still too early to tell what percentage of people will develop permanent loss, he said.

Material from Globe wire services was used in this report.