DAVID FOLKENFLIK, HOST:
The way we think about COVID-19 has changed over time. Now we're learning that our brains actually change when we're infected with the disease. According to a new study led by the University of Oxford's professor Gwenaelle Douaud, people with even just a mild case of COVID experienced brain shrinkage and tissue damage. The study was published this week in the journal Nature. Tom Nichols is a professor of neuroimaging statistics at the University of Oxford, and he's a co-author of the study and joins us now. Welcome.
TOM NICHOLS: Thank you.
FOLKENFLIK: Professor Nichols, your study was large and peer-reviewed. Tell us a bit about your main findings.
NICHOLS: We were able to look at the brains of 785 different individuals. These are older adults aged between 50 and 80, and we were able to scan their brains before they got COVID. And then we imaged them about three years later after some of them had gotten COVID. And the other thing that's important is that we found the 400 people who had COVID, and then we carefully found other individuals who were similar to them as possible but did not have COVID. So we tried to match them in terms of age, sex, blood pressure, obesity, et cetera, so that they would serve as the best possible controls.
And then we looked for changes in the brain over this in an interval, comparing the changes in the brain of subjects that had COVID to those who did not. And what we found is reduction. So basically, people's brain volumes were smaller after getting COVID than the people who did not get COVID. And it's only because of the U.K. Biobank that we're able to do this. So this is this remarkable resource where half a million people have volunteered to contribute their health and genetic data, and a subset of them also got detailed brain scans.
FOLKENFLIK: You look at the question of the brain. Your study found actual loss of gray matter in the brain. What is gray matter? What does it mean when somebody loses some of that?
NICHOLS: Gray matter is the part of the brain that is where kind of the numbers get crunched. And so we generally look at the gray matter because we are all slightly losing some gray matter over time from about age 20. But we do know that towards later life, you start to lose it more quickly, and those individuals who are losing the most, who have the least amount of gray matter, are most at risk for dementia. So that's why we care about it.
FOLKENFLIK: What are the long-term implications for patients including, as you mentioned, dementia?
NICHOLS: Well, that is to be seen. So this study covered individuals for three years. So we measured them before they got COVID and then three years later. The average time after COVID was less than a year. And so it is to be seen. It is possible that these individuals will catch up with the individuals who didn't have COVID. Or this could basically be changing the trajectories for these subjects. That is something that will have to be done with further research and following these individuals into the future.
FOLKENFLIK: What were some of the limitations of this study?
NICHOLS: It is a self-selected sample. People did volunteer to become members of the U.K. Biobank. So it is known that the U.K. Biobank undersamples underrepresented minorities. And so that's one limitation. And I'd say the other limitation is that - an important question is, is this very specific to COVID? So we did look at subjects that got pneumonia in this time who are not in this sample, and they did not show these sort of changes. But we can't rule out that some of this is just the impact of getting a very serious disease.
FOLKENFLIK: What should people actually have as a takeaway from your findings?
NICHOLS: I would say the main takeaway is that COVID is affecting lots of different parts of your body, not just the lungs but also the brain. So it's a serious disease. I think the actual takeaway for any one individual are kind of limited in a way because we knew already that COVID is bad. I think this is most important for scientists who are trying to understand the precise impacts that COVID is having on our body.
FOLKENFLIK: Tom Nichols is a professor of neuroimaging statistics at the University of Oxford. Tom Nichols, thanks so much.
NICHOLS: Thank you. Transcript provided by NPR, Copyright NPR.
