Covid-19 causes changes in the brain, even in mild cases, says study

People who have had Covid-19, even in mild cases, may have accelerated brain aging and other changes, according to a new study.

The research, published on Monday (7) in the journal Nature, is believed to be the largest of its kind. The study revealed that the brains of those who had Covid-19 had greater gray matter loss and organ tissue abnormalities compared to those who did not have the disease. Many of these changes occurred in the area of ​​the brain related to the sense of smell.

“We were quite surprised to see clear differences in the brain, even with mild infection,” he told CNN lead author Gwenaëlle Douaud, an associate professor of neuroscience at the University of Oxford, via email.

Gwenaëlle and her colleagues evaluated brain scans of 401 people who had Covid-19 between March 2020 and April 2021, before infection and an average of 4.5 months after infection. They compared the results with brain scans of 384 uninfected people similar in age, socioeconomic status and risk factors such as blood pressure and obesity. Of the 401 infected people, 15 were hospitalized.

The 785 participants were aged between 51 and 81 and were part of the UK Biobank, a continuous UK government health database of 500,000 people, started in 2012.

The researcher explained that it is normal for people to lose 0.2% to 0.3% of gray matter every year in the memory-related areas of the brain as they age, but in the study’s assessment, people who were infected with the coronavirus lost an additional 0.2% to 2% of tissue compared to those who were not infected.

In addition to imaging tests, participants were tested for their executive and cognitive function using the Trail Making Test, a tool to help detect cognitive impairments associated with dementia and test a person’s speed and brain processing function.

The researchers found that those who had the most brain tissue loss also performed the worst on this test.

While the areas of the brain most affected appear to be related to the olfactory system, Gwenaëlle said it was unclear why this was the case.

“As the abnormal changes we see in the brains of infected participants may be partially related to the loss of smell, it is possible that regaining it could cause these brain abnormalities to become less pronounced over time. Likewise, it is likely that the harmful effects of the virus (either direct or indirect via inflammatory or immune reactions) diminish over time after infection. The best way to find out would be to examine these participants again in a year or two,” she said.

Gwenaëlle added that the researchers expect to run new imaging and cognitive performance tests on the participants in one to two years.

And while the study finds some association between infection and brain function, it’s still unclear why. Previous studies have shown that people with significant and repeated loss of smell also have an associated loss of gray matter. However, this study did not assess whether people actually had a loss of smell.

The authors cautioned that the findings are snapshots of a moment, but noted that they “raise the possibility that the long-term consequences of SARS-CoV-2 infection could contribute over time to Alzheimer’s disease or other forms of dementia.” .

The findings were relevant, but not enough to cause alarm, said Richard Isaacson, a neurologist and director of the Center for Brain Health at Florida Atlantic University. The researcher was not involved in the study.

Isaacson said the results were relevant for clinicians, but added that the overall impact on individuals is difficult to determine and may be small. “It’s really difficult to know the long-term clinical impact and the impact on quality of life in a situation like this,” he said.

“The brain can be affected by other mechanisms, such as immune, inflammatory, vascular, or psychological/behavioral changes, but not by direct infection,” said Alan Carson, a professor of neuropsychiatry at the Center for Clinical Brain Sciences at the University of Edinburgh, who has not participated in the study.

“What this study almost certainly shows is the impact, in terms of neural changes,” he said. “But I don’t think this helps us understand the mechanisms that underpin cognitive change after Covid infection.”

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Source: CNN Brasil

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