Even the mildest covid-19 causes changes in the brain, study finds

Even people who have had only mild cases of Covid-19 may have accelerated aging and undergone other changes in the brain, according to a new study.

The research, published Monday in the journal nature, is the largest of its kind. And he found that the brains of those who had Covid-19 had greater loss of gray matter and recorded abnormalities in brain tissue, compared to those who did not have the disease. Many of these changes involved the area of ​​the brain related to smell.

“We were quite surprised to see clear differences in the brain, even in mild infections”said lead author CNNGwenaëlle Douaud, associate professor of neuroscience at the University of Oxford, by email.

Douaud and his colleagues evaluated the brain imaging of 401 people who had Covid-19 between March 2020 and April 2021, before infection and, on average, four and a half months after it. They compared the results with brain imaging of 384 uninfected people, with the same age, the same socioeconomic level and the same risk factors, such as blood pressure and obesity. Of the 401 people infected, 15 had been hospitalized.

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

Douaud explained that it’s normal for people to lose between 0.2 and 0.3 percent gray matter each year, in memory-related areas, as they age, but in the study’s assessment, people who had been infected with the coronaviruses lost 0.2 to 2% more tissue than those who were not infected.

In addition to imagery, participants’ executive and cognitive functions were tested using the Trail Making Test, a tool used to help detect cognitive impairment associated with dementia and test processing speed and functioning. of the brain. The researchers found that those with the greatest loss of brain tissue also fared worse on scans.

Although the areas of the brain most affected appear to be related to the olfactory system, Douaud said the reason was unclear.

“Since the abnormal changes we see in the brains of infected participants may be partially related to the loss of smell, it is possible that their recovery may make these brain abnormalities less obvious over time. Likewise, the harmful effects of the virus (both direct and indirect, via inflammatory or immune reactions) are likely to diminish over time after infection. The best way to find out would be to test participants again in a year or two,” she said.

Douaud added that the researchers plan to do new images and other tests on the participants within the next year or two.

Although the study established an association between the infection and brain function, the reason for this link is still unclear. Previous studies have shown that people with significant and recurrent loss of smell have an associated loss of gray matter. However, this study does not assess whether people actually lost their sense of smell.

The authors cautioned that the results only relate to this specific time period, but acknowledged that “the possibility increases that the long-term consequences of SARS-CoV-2 infection may, over time, contribute to the disease of ‘Alzheimer’s or other forms of disease’. madness”.

The results were notable but not significant enough to cause alarm, said Richard Isaacson, a neurologist and director of Florida Atlantic University’s Institute for Brain Health. Isaacson was not involved in the study.

He said the results were remarkable for clinicians, but added that the overall impact at the individual level was difficult to determine and could be small. “It’s very 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 direct infection,” said Alan Carson, professor of neuropsychiatry at the Institute for Clinical Brain Sciences in the University of Edinburgh. who did not participate in the study.

“What this study almost certainly demonstrates is the impact at the level of neurological changes,” he said. “But I don’t think it helps to understand the mechanisms underlying cognitive change after being infected with covid.”

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